NCHurricane2009's Blog

2013 Atlantic Hurricane Season Birdseye Discussion #80

By: NCHurricane2009, 6:40 AM GMT on August 31, 2013

...SATURDAY AUGUST 31 2013 2:40 AM EDT...
Central Atlantic tropical wave is now en route to the Lesser Antilles and eastern Caribbean region. Because the thunderstorm activity remains reduced and computer model support has been on the decline in the last few days...I have cancelled it as a special feature on this blog. See paragraph P8 for update on this tropical wave.

Tropical wave emerging from the west coast of Africa has been upgraded to Invest 96-L due to improved organization and is headed toward the Cape Verde Islands in the next 48 hours. See paragraph P9 for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_30_2013_1515Z_zps75840ead.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released WPC analysis.

Any features boxed in green were mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's newer longer term 5-day outlook. Systems that I consider special features have less to do with whether they are boxed in green and more to do with whether I think their is a high risk of eventual tropical cyclone formation from that system.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_30_2013_1515Z_zps37bbddc6.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Next shortwave upper trough and associated surface cyclone has entered the top-center of the above charts from northern Canada in the last 48 hrs. Western convergence of this shortwave supports 1022 mb surface ridge building into Hudson Bay.

P2...Upper ridge persists over the central US. Southern convergence of upper ridge supports 1017 mb surface ridge over the US Gulf coast. A shortwave upper trough is moving through this upper ridge while traveling from the southwest US and into the central US in the last 48 hours...with its western convergence currently supports 1019 mb ridge over the western US and its eastern divergence supporting 1007 mb frontal depression moving through the Great Lakes region. To the east and northeast of the upper ridge...the north half of large upper trough in the NW Atlantic has split into a shortwave and associated frontal cyclone that has moved from northern Canada...across southern Greenland...and into the NE Atlantc in the last 48 hrs (western convergence of this shortwave supports 1031 mb ridge south of Greenland). Remainder of this upper trough persists in the NW Atlantic while its eastern divergence supports frontal cyclone that has deepend from 1008 to 996 mb while the frontal cyclone has moved into Atlantic Canada. Western convergence of this upper trough supports 1018 mb ridge over the eastern US.

P3...Shortwave upper trough previously over the north-central Atlantic has been absorbed by paragraph P2 upper trough moving into the NE Atlantic. Cut-off upper vortex persists in the vicinity of southern Florida...and a western fragment of this vortex is retrograding westward across the southern Gulf of Mexico around the paragraph P2 central US upper ridge.

P4...NE Atlantic upper ridge is moving into western Europe while associated with warm air advection ahead of paragraph P2 frontal cyclone moving into the NE Atlantic. Meanwhile...a mid-latitude central Atlantic upper anticyclone is flaring up due to warm air advection ahead of 996 mb frontal cyclone mentioned in paragraph P2.

P5...Surface ridge dominating much of the open Atlantic remains anchored by 1029 mb center north of the Azores...but the dominant center is transitioning to 1031 mb center south of Greeland mentioend in paragraph P2. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P6...Large eastern Atlantic and Caribbean low-latitude upper ridge has bridged into one upper ridge currently covering all of the tropical latitudes. Adjacent axis of upper vorticity...sandwiched between the low-latitude upper ridge and central Atlantic upper anticyclone in paragraph P4...stretches from the waters NE of the Lesser Antilles all the way to the Canary Islands in the northeastern Atlantic. A fragment of this upper vorticity has fractured off while escaping into western Europe...and fragments of this upper vorticity are expected to retrograde westward into the NE Caribbean region while orbiting around paragraph P4 central Atlantic upper anticyclone.

P7...Tropical wave previously approaching the Lesser Antilles is now in the NE Caribbean and is currently suppressed by westerly vertical shear at the southwest end of paragraph P6 axis of upper vorticity.

P8...Tropical wave previously in the waters midway between the Cape Verdes and Lesser Antilles has become less organized while moving toward the Lesser Antilles. Despite being embedded in favorable environment of low shear below paragraph P6 low-latitude upper ridge axis...the thunderstorms have become less organized and biased to the east while the west half of the system appears embedded in a pocket of Saharan dry air mentioned in paragraph P5. I have dropped this tropical wave as a special feature on this blog while the system has become less organized and while computer model support has been on the decline over the last few days. In addition...their is uncertainty in further devleopment due to the axis of upper vorticity looming just to the north (mentioned in paragraph P6) that could begin shearing this system if the tropical wave shifted a little north or if the upper vorticity shifts a little south. The CMC model is currently the only model still showing development when the tropical wave reaches the eastern Caribbean as it sees the axis of upper vorticity breaking up enough to allow a healthy upper anticyclone to build over the tropical wave. However taking CMC superficially as it usually over-forecasts tropical cyclone development.

P9...A tropical wave emerging from the west coast of Africa continues to produce a widespread region of thunderstorms...but the activity is now more consolidated and organized at a location due east of the Cape Verde Islands. The increase in organization and development potential in the favorable low shear and enhanced outflow of low-latitude upper ridge mentioned in paragraph P6 has warranted its upgrade to Invest 96-L in the last 48 hours. Given the recent string of false-alarms when it comes to development potential with tropical waves...I would prefer to see additional organization from current levels before considering this a special feature with a high/imminent risk of tropical cyclone formation. Regardless of further development...expect an increase in squally weather for the Cape Verde Islands in the next 48 hours...with the potential for development possibly declining by 72 hours and beyond as the tropical wave could interact with less favorable axis of upper vorticity mentioned in paragraph P6.

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2013 Atlantic Hurricane Season Birdseye Discussion #79

By: NCHurricane2009, 10:56 AM GMT on August 29, 2013

...THURSDAY AUGUST 29 2013 7:00 AM EDT...
Eastern Atlantic tropical wave has moved into the central Atlantic while its cloud field shows spiral banding. Although the thunderstorm activity has weakened in the last 24 hours...still monitoring the wave for additional development. See special feature section below for additional details.

A tropical wave is emerging from the west coast of Africa with abundant thunderstorm activity. See paragraph P8 for details.

Starting with this post...I have added a statement in the "atmospheric features chart" section clarifying the convention I have used all along for boxing features in green. I have also clarified which systems I consider special features on this blog...which does not necessarily have to do with whether or not the system is boxed in green.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_28_2013_1815Z_zps102bf235.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1923Z-released WPC analysis.

Any features boxed in green were mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's newer longer term 5-day outlook. Systems that I consider special features have less to do with whether they are boxed in green and more to do with whether I think their is a high risk of eventual tropical cyclone formation from that system.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_28_2013_2345Z_UPDATED_zps9edc89e1.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...CENTRAL ATLANTIC TROPICAL WAVE...
Still watching tropical wave in the waters midway between the Cape Verdes and Lesser Antilles while its low clouds show signs of spiral banding. Despite being embedded in a moist environment as seen in the above thermo chart...and despite being in a favorable atmospheric setting of low shear and enhanced outflow beneath eastern Atlantic upper ridge (paragraph P5)...its thunderstorm activity has died down. Comparing the thermo chart above to the thermo chart in previous discussion #78...some of the shrinkage of the Saharan dry air mentioned in paragraph P4 is due to this tropical wave...so perhaps the wave has sputtered while coughing on a bit of the dry air while successfully moistening it out. Regarding upper winds...model runs agree that in general the tropical wave will slip south of the embedded axis of unfavorable upper vorticity mentioned in paragraph P5 while the eastern Atlantic and Caribbean portions of the paragraph P5 upper ridge begin to bridge. This should keep the tropical wave in favorable atmospheric conditions. Therefore I am maintaining this tropical wave as a special feature on this blog while considering it a high risk of eventual tropical cyclone formation. Marine interests in the open tropical Atlantic east of the Lesser Antilles...as well as interests in the Lesser Antilles and eastern Caribbean Islands...should continue to stay tuned over the next few days. Although this tropical wave has yet to be introduced into the National Hurricane Center's traditional 48-hour tropical weather outlook...it has been mentioned in their new 5-day outlook product during the few days.

...MID-LATITUDES DISCUSSION...
P1...Upper ridge persists over the central US. Southern convergence of upper ridge supports 1020 mb surface ridge over the eastern US. A shortwave upper trough over the southwest US will be orbiting anticyclonically around the upper ridge...and its western convergence currently supports 1019 mb ridge over the 4-corners states. To the east and northeast of the upper ridge...shortwave upper trough impulse in the NW Atlantic (with associated surface 1008 mb frontal depression) has merged with upper trough from northern Canada. Eastern divergence of the upper trough from northern Canada supports frontal cyclone that has moved into Greenland while western convergence of the upper trough supports 1025 mb ridge over NE Canada.

P2...Shortwave upper trough and frontal cyclone previously southeast of Greenland has ejected northeast out of the scope of this discussion. Shortwave upper trough previously over Newfoundland and NW Atlantic has moved into the north-central Atlantic while the cyclone deepens to 1004 mb. Cut-off upper vortex persists in the vicinity of southern Florida...and a western fragment of this vortex is retrograding westward across the southern Gulf of Mexico around the paragraph P1 central US upper ridge. Eastern divergence of the upper vortex supports some disturbed weather and associated surface trough over the central Bahamas.

P3...NE Atlantic upper ridge persists due to warm air advection ahead of 1004 mb cyclone metioned in paragraph P2.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1028 mb center north of the Azores supported by southern convergence of paragraph P3 NE Atlantic upper ridge. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Large eastern Atlantic and Caribbean low-latitude upper ridge persists. This upper ridge remains split by embedded axis of upper vorticity stretching from the waters east of the Lesser Antilles all the way to the Canary Islands in the northeastern Atlantic. Eastern divergence of this upper vorticity supports surface trough southwest of the Azores. A fragment of this upper vorticity has fractured off while escaping into western Europe.

P6...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently moving across the Yucatan. Occasional thunderstorms east of the wave axis persist due to enhanced poleward outflow at the west end of paragraph P5 Caribbean/eastern Atlantic upper rige.

P7...Tropical wave continues to approach the Lesser Antilles and is currently suppressed by dry Saharan air mentioned in paragraph P4.

P8...A tropical wave emerging from the west coast of Africa is producing a widespread region of thunderstorms extending all the way to the waters south of the Cape Verde Islands this morning. This tropical wave has been introduced into the National Hurricane Center traditional 48-hour Tropical Weather Outlook due to its development potential beneath favorable low shear and enhanced outflow of paragraph P5 upper ridge. Although the large expanse of thunderstorms is impressive...I prefer to see a more consolidated and organizing system before considering this a special feature on this blog. In addition...the National Hurricane Center outlook states the wave could later on encounter unfavorable upper winds associated with the embedded axis of upper vorticity in the upper ridge mentioned in paragraph P5.

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2013 Atlantic Hurricane Season Birdseye Discussion #78

By: NCHurricane2009, 7:15 AM GMT on August 28, 2013

...WEDNESDAY AUGUST 28 2013 3:15 AM EDT...
Eastern Atlantic tropical wave has become a little better organized within the last day while continuing to have the potential for additional development. See special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_27_2013_2015Z_zps3bca4c48.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1929Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_27_2013_2015Z_zps21fe9af6.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Tropical wave southwest of the Cape Verde Islands is entering the waters midway between the Cape Verdes and Lesser Antilles while becoming better organized as ittakes advantage of enhanced outflow and low shear beneath eastern Atlantic upper ridge (paragraph P5). The southwest end of axis of upper vorticity embedded in eastern Atlantic upper ridge is breaking off and retrograding westward and away...keeping the tropical wave under the favorable conditions. Therefore I am maintaining this tropical wave as a special feature on this blog while considering it a high risk of eventual tropical cyclone formation. Marine interests in the open tropical Atlantic east of the Lesser Antilles...as well as interests in the Lesser Antilles...should continue to stay tuned over the next few days. Although this tropical wave has yet to be introduced into the National Hurricane Center's traditional 48-hour tropical weather outlook...it has been mentioned in their new 5-day outlook product during the last couple of days.

...MID-LATITUDES DISCUSSION...
P1...Upper ridge persists over the central US. Southern convergence of upper ridge supports 1023 mb surface ridge over the eastern US previously supported by W Atlantic upper trough mentioned in paragraph P2. To the north of the upper ridge...a shortwave upper trough impulse is arriving into the NW Atlantic from the NE US while associated 1007 mb frontal depression is over Atlantic Canada. Another such impulse with 1008 mb frontal depression is currently over north-central Ontario about to cross over southern Hudson Bay. Further north...an upper trough and associated surface frontal cyclone that has persisted over northern Canada is entering the top-center of the above atmo chart while the western convergence of this upper trough supports surface ridge over northern Hudson Bay.

P2...Upper trough over the western Atlantic has broken into a few shortwave upper troughs...including one southeast of Greenland whose eastern divergence is supporting 1000 mb frontal cyclone...another shortwave over eastern Newfoundland and NW Atlantic whose eastern divergence supports 1011 mb frontal cyclone...another shortwave in the vicinity of Bermuda...and cut-off upper vortex over south Florida. The National Hurricane Centerin their 48-hour Tropical Weather Outlook has highlighted the upper vortex as its eastern divergence supports some disturbed weather over the W Bahamas...W Cuba...and south Florida...in addition to a surface trough over the W Bahamas and waters east of Florida. However tropical development appears unlikely due to high surface pressures of paragraph P1 eastern US surface ridge and paragraph P4 open Atlantic surface ridge.

P3...Cut-off upper vortex previously over the Azores has become assimilated into axis of upper vorticity mentioned in paragraph P5 below. NE Atlantic upper ridge persists.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1030 mb center north of the Azores supported by southern convergence of paragraph P3 NE Atlantic upper ridge. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Upper anticyclone persists over central Mexico whose upper outflow supports continued cloudiness and thunderstorms even though the remnant low of Fernand has dissipated. Large eastern Atlantic and Caribbean low-latitude upper ridge persists. This upper ridge remains split by embedded axis of upper vorticity stretching from the waters east of the Lesser Antilles and into the waters south of the Azores. A fragment of this upper vorticity has fractured off while escaping into western Europe and NW Africa.

P6...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently moving across Central America and the western Caribbean while it is producing an impressive area of thunderstorms supported by enhanced poleward outflow at the west end of paragraph P5 Caribbean/eastern Atlantic upper rige. Tropical development is not expected here due to land interaction with Central America.

P7...Tropical wave previously midway between the Cape Verdes and Lesser Antilles is approaching the northern Lesser Antilles and is currently suppressed by dry Saharan air mentioned in paragraph P4.

Updated: 10:23 AM GMT on August 29, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #77

By: NCHurricane2009, 11:18 AM GMT on August 27, 2013

...TUESDAY AUGUST 27 2013 7:15 AM EDT...
Tropical Storm Fernand has dissipated over inland central Mexico as of yesterday afternoon and is no longer a special feature on this blog. However additional rains from the remnants continue the flash flood and mudslide potential.

Small tropical low in the central Atlantic mentioned in special update #76B has lost its identity in the Intertropical Convergence Zone (ITCZ) and therefore is no longer a special feature on this blog.

Still monitoring the potential for eastern Atlantic tropical wave to develop into a tropical cyclone. See special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_26_2013_2345Z_zps9b39d612.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0116Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_27_2013_0345Z_zps994f524b.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE..
Tropical wave previously emerging from Africa has passed south of the Cape Verde Islands and is now producing a respectable thunderstorm cluster southwest of the islands this morning. Computer models suggest that the southwest end of axis of upper vorticity embedded in eastern Atlantic upper ridge (paragraph P5) will break off and retrograde westward and away. This will allow the tropical wave to potentially develop in favorable environment of enhanced outflow and low shear beneath the east Atlantic upper ridge as some computer model runs continue to suggest. Therefore I am maintaining this tropical wave as a special feature on this blog while considering it a high risk of eventual tropical cyclone formation. Marine interests in the open tropical Atlantic east of the Lesser Antilles and west of the Cape Verde Islands should continue to stay tuned over the next few days...

...MID-LATITUDES DISCUSSION...
P1...Upper ridge has built across the central US. To the north of the upper ridge...shortwave upper trough impulse and associated 1005 mb frontal depression has moved from eastern Manitoba and into Atlantic Canada. Another such impulse with 1006 mb frontal depression is currently over NE Manitoba crossing into Hudson Bay.

P2...Upper trough previously over the eastern US and eastern Canada is now in the western Atlantic. Its south end appears to be cutting off into an upper vortex over south Florida to the southeast of the paragraph P1 central US upper ridge. The developing cut-off upper vortex has produced some disturbed weather over the western Bahamas region with its eastern divergence. Lengthy cold front supported by eastern divergence of upper trough extends across the north and western Atlantic. Previous 1014 mb frontal depression south of Newfoundland has deepened to 1002 mb and is currently located east of Newfoundland. A new frontal depression of 1012 mb has developed ENE of Bermuda. Western convergence of the upper trough supports 1022 mb surface ridge over the eastern US.

P3...Shortwave upper trough in the north-central Atlantic has cut-off into an upper vortex over the Azores while becoming trapped due south of amplifying NE Atlantic upper ridge pumped up by warm air advection ahead of 1002 mb cyclone mentioned in paragraph P2 above.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1029 mb center north of the Azores supported by southeastern convergence of paragraph P3 NE Atlnatic upper ridge. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Upper anticyclone associated with the latent heat release and upper outflow of Fernand and its remnants is currently centered over central Mexico. Relatively lower pressures east of the upper anticyclone supports upper vortex currently located over Panama. To the east of the upper vortex...large eastern Atlantic and eastern Caribbean low-latitude upper ridge persists. This eastern Atlantic upper ridge remains split by embedded axis of upper vorticity stretching from the waters west of the Cape Verde Islands and into the Canary Islands and Europe's Iberia peninsula.

P6...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently moving across the central Caribbean Sea while producing pockets of thunderstorms supported by split flow upper divergence between paragraph P5 upper vortex over Panama and paragraph P5 eastern Caribbean/eastern Atlatnic upper ridge.

P7...Tropical wave previously west of the Cape Verde Islands is now midway between the Cape Verdes and Lesser Antilles while suppressed by westerly vertical shear along south side of axis of upper vorticity mentioned in paragraph P5 and unfavorable dry Saharan air mentioned in paragraph P4. However its south end is embedded in the ITCZ where it is producing a broad region of thunderstorms enhanced by poleward upper outflow into the aformentioned upper vorticity.

Updated: 10:22 AM GMT on August 29, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #76B (Special Update)

By: NCHurricane2009, 9:12 AM GMT on August 26, 2013

...MONDAY AUGUST 26 2013 5:12 AM EDT...
Overnight...the expanse of Tropical Storm Fernand's intense thunderstorms have increased. This means the risk of flash flooding and mudslides in mountainous terrain is possible over a wider area than previously shown by the impact swath in Figure 1 of discussion #76. Based on the latest colorized infrared satellite imagery...the risk includes areas in central Mexico between 25N and 15N latitude including the Isthmus of Tehuentepec currently overspread by the southeastern bands of Fernand.

Small 1012 mb tropical low midway between the Cape Verde Islands and Lesser Antilles...mentioned in paragraph P7 of discussion #76...has become better organized overnight while passing 50W longitude while producing a circular area of thunderstorms. Based on the latest upper wind forecast...this surface low for the next few days will continue to be embedded in a favorable environment of low shear and enhanced upper outflow beneath eastern Caribbean and eastern Atlantic upper ridge mentioned in paragraph P5 of discussion #76. Therefore I am now considering this a special feature with a high risk of eventual tropical cyclone formation. Interests in the southern Lesser Antilles...northeastern Venezuela...Aruba...Bonaire...Curacao...and marine interests in the southeastern Caribbean should monitor the progress of this feature.

No update in regards to special feature tropical wave in discussion #76 that has recently emerged from Africa.

Return to full discussion #76 for an assessment on the rest of the Atlantic tropics.

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2013 Atlantic Hurricane Season Birdseye Discussion #76A (Special Update)

By: NCHurricane2009, 12:36 AM GMT on August 26, 2013

...SUNDAY AUGUST 25 2013 8:36 PM EDT...
Aircraft Reconnaissance has reached tropical depression six and has determined that previous estimates using surface observations and satellite organization had under-predicted the true strength of the cyclone. The depression has been upgraded to Tropical Storm Fernand of 45 mph maximum sustained winds. In addition...the center has been fixed further southwest from previous estimates such that the NHC has adjusted their forecast track further south. Since my previous forecast track in discussion #76 already had a southward bias...I am not making much adjustment to that track. The following is my updated intensity forecast in lieu of the upgrade to Tropical Storm Fernand:

7 PM Sun Aug 25 2013...45 mph...initial
10 PM Sun Aug 25 2013...50 mph...3 hr (Landfall)
4 AM Mon Aug 26 2013...40 mph...9 hr
10 AM Mon Aug 26 2013...35 mph...15 hr (Dissipating)

The NHC forecast intensity suggests a peak of 60 mph for the landfall later tonight. Although their has been a very recent and impressive storm burst over the center as seen on satellite to support the NHC forecast...with the center currently close to the coast I do not think that Fernand will quiet make it to that strength before landfall.

Return to full discussion #76 for an assessment on the rest of the Atlantic tropics.

Updated: 12:38 AM GMT on August 26, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #76

By: NCHurricane2009, 11:01 PM GMT on August 25, 2013

...SUNDAY AUGUST 25 2013 7:01 PM EDT...
Disturbance moving across the Yucatan yesterday has become Tropical Depression Six in the Bay of Campeche as of this afternoon and early evening. See tropical depression six special feature section for additional details.

A tropical wave emerging from the west coast of Africa has high risk for eventual tropical cyclone formation. See second special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_25_2013_1145Z_zpsc0794a73.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1329Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_25_2013_1145Z_zps9e6f9221.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION SIX...
Tropical wave Invest 95-L has moved into the Bay of Campeche and has intensified to Tropical Depressin Six this afternoon. Thunderstorm latent heat release associated with the tropical cylcone continues pumping up its upper anticyclone such that the unfavorable upper vortex has been pushed further west into Mexico...and therefore we can expect a high chance of the system intensifying further into a tropical storm before landfall tonight. My forecast in Figure 1 is similar to the NHC's except that my forecast peak intensity is a bit lower and my forecast track is a bit south of the NHC's based on how the cyclone's center is tracking on visible satellite animation. The forecast tracks in Figure 1 depened on the cyclone staying a shallower/weakish system that is steered by southwest quadrant of paragraph P2 eastern US low-level ridge such that it gradually curves more northward (a stronger/taller system would have been steered more west while feeling some influence from paragraph P1 high-level central US ridging).

 photo Aug_25_2013_TD_Six_Forecast_zps0c1fc75f.png
Figure 1: My versus the NHC's forecast for Tropical Depression Six

Impact swath in Figure 1 is based on the coldest cloud tops in the colorized AVN infrared color scheme in the circular core of tropical derpession six. This is where I believe it is most likely that the cyclone will drop its heaviest rainfall...although their are some outer spiral bands north of the core that could drop some additional rainfall north of the impact swath.

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Satellite suggests a strong tropical wave with rotation and semi-organized thunderstorms is emerging from Africa and into the waters southeast of the Cape Verde Islands. Computer models suggest that the southwest end of axis of upper vorticity embedded in eastern Atlantic upper ridge (paragraph P5) will break off and retrograde westward and away. This will allow the tropical wave to potentially develop in favorable environment of enhanced outflow and low shear beneath the east Atlantic upper ridge as many of the computer model runs tonight suggest. Therefore I have already upgraded this tropical wave to a special feature on this blog while considering it a high risk of eventual tropical cyclone formation. Marine interests in the open tropical Atlantic east of the Lesser Antilles and west of the Cape Verde Islands should stay tuned over the next few days...

...MID-LATITUDES DISCUSSION...
P1...Upper ridge has built across the central US. To the northeast of the upper ridge...shortwave upper trough from Canada's Hudson Bay has arrived into Greenland while its eastern divergence supports 998 mb frontal depression. Divergence northwest of central US upper ridge supports 1006 mb frontal depression over eastern Manitoba.

P2...Upper trough persists across the eastern US...eastern Canada...and the high seas between Greenland and Canada. Lengthy cold front supported by eastern divergence of upper trough extends across the north and western Atlantic...and reaches across the eastern US Gulf coast. New 1014 mb depression south of Newfoundland is located along the cold front. Low-level warm air advection ahead of the cold front supports small NW Atlantic upper anticyclone. Western convergence of the upper trough supports 1031 mb surface ridge over the eastern US.

P3...Shortwave upper trough in the NW Atlantic has moved into the north-central Atlantic in advance of paragraph P2 upper trough. Relatively warmer air ahead of this upper trough supports NE Atlantic upper ridge.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1032 mb center north of the Azores supported by southeastern convergence of paragraph P3 NE Atlnatic upper ridge. Recently the surface 1032 mb center has become vertically stacked with the upper ridge center. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Upper vorticity previously in the western Gulf of Mexico has been pushed into eastern Mexico due to latent heat release associated with Tropical Depression Six. Upper anticyclone associated with the latent heat release and upper outflow of tropical depression six is currently centered over the northern Yucatan. Relatively lower pressures east of the upper anticyclone supports upper vortex currently located south of Jamaica. To the east of the upper vortex...large eastern Atlantic and eastern Caribbean low-latitude upper ridge persists. This eastern Atlantic upper ridge remains split by embedded axis of upper vorticity stretching from the waters west of the Cape Verde Islands and into the Canary Islands and Morocco.

P6...Tropical disturbance in the northern Gulf of Mexico has become absorbed by tail end of cold front mentioned in paragraph P2.

P7...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently moving across the eastern Caribbean Sea while its thunderstorm activity has increased due to enhanced poleward outflow at the west end of paragraph P5 eastern Atlantic/eastern Caribbean upper ridge. Small 1012 mb low currently midway between the Cape Verdes and Lesser Antilles left behind by this tropical wave days ago has seen some increase in thunderstorms but remains largely suppressed in enviornment of dry Saharan air mentioned in paragraph P4.

P8...Tropical wave previously southwest of the Cape Verde Islands is currently west of the islands has seen a decrease in organization and intensity of thunderstorms while becoming exposed to unfavorable southerly vertical shear along east side of axis of upper vorticity mentioned in paragraph P5 and unfavorable dry Saharan air mentioned in paragraph P4.

Updated: 12:20 AM GMT on August 26, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #75A (Special Update)

By: NCHurricane2009, 1:33 AM GMT on August 25, 2013

...SATURDAY AUGUST 24 2013 9:35 PM EDT...
Visible satellite animation before susnet suggested the surface rotation of disturbance Invest 95-L was working its way west-northwest into the warm waters of the Bay of Campeche. In addition...the lastest satellite-derived upper-level winds suggested the thunderstorm activity of 95-L has produced enough latent heat release such that its upper anticyclone has become better defined and wedged out the western Gulf of Mexico upper vortex. Therefore I am considering this system a special feature with a very high probability of tropical cyclone formation in the Bay of Campeche in the next 24 hours. Expect in the next 48 hours for this system to move into the east-facing coast of Mexico while steered west-northwest by surface ridge currently located over the northeastern US and southeastern Canada mentioned in paragraph P2 of discussion #75. Given the favorable upper winds and warm waters...this system has the potential to spin up quickly into a strong tropical storm. For such a scenario...interests along the east-facing Bay of Campeche and Gulf of Mexcio coasts of Mexico should be ready to prepare for strong winds near such a storm center...and interests further inland (particularly in mountanious terrain) shoudl be ready to prepare for the potential of flash floods and mudslides.

The disturbance in the northern Gulf of Mexico mentioned in paragraph P6 of discussion #75 has been re-analyzed as a surface trough just offshore of Louisiana this past afternoon while thunderstorms have re-devloped with this system. The upper winds have become more favorable while the thunderstorm latent heat release has caused the system to develop its own upper anticyclone and while the shearing upper westerly winds at the base of the upper trough mentioned in paragraph P2 of discussion #75 have moved away to the east. Based on the surface trough being depicted as an east-west structure which is confirmed by visible satellite animation of the area just before sunset...this system does not have as well defined of a structure as Invest 95-L further to the south. Therefore I will assume that 95-L to the south will develop faster such that it will dominate the low-level inflow and upper-level outflow in the Gulf region such that this system will struggle to develop further...and therefore I am currently not considering this system a special feature. Regardless of development...expect this system to track generally west to west-northwest while steered between the cyclonic circulation of 95-L to the south and northeastern US and southeastern Canada surface ridge to the north mentioned in paragraph P2 of discussion #75. Therefore expect heightened rainfall to potentially spread into southern Louisiana and the upper Texas coast over the next couple of days

Return to full discussion #75 for an assessment on the rest of the Atlantic tropics.

Updated: 1:39 AM GMT on August 25, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #75

By: NCHurricane2009, 8:03 PM GMT on August 24, 2013

...SATURDAY AUGUST 24 2013 4:00 PM EDT...
Dry Saharan air in the Atlantic tropics appears to have diminished in areal extent. In addition...a disturbance moving across the Yucatan peninsula has the potential for development while continuing west-northwest into the Bay of Campeche waters as outlined in paragraph P7 below. Therefore I have resumed daily discussions on the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_24_2013_0615Z_zps7405ad35.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0726Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_24_2013_0615Z_zpsf2b34e49.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper ridge has built across the central US. To the north of the upper ridge...the next shortwave upper trough and surface frontal system in the mid-latitudes is entering the upper-left of the above charts from Canada's Hudson Bay.

P2...Upper trough moving across Hudson Bay during previous discussion #74 is currently across the eastern US...eastern Canada...the high seas between Greenland and Canada...and Greenland. Associated surface low supported by eastern divergence of upper trough is currently over Iceland while the lenghty cold front extending from the surface low is entering the western Atlantic...and reaches into the southeastern US and central US. Western convergence of the upper trough supports 1026 mb surface ridge over SE Canada and the NE US.

P3...Shortwave upper trough and vigorous frontal cyclone over the north-central Atlantic mentioned in previous discussion #74 has since ejected northeastward out of the scope of the above charts...but leaves behind a shortwave upper trough and associated surface trough currently located in the NW Atlantic. Upper vortex over Illinois mentioned in previous discussion #74 has since moved eastward into the Atlantic waters in the vicinity of Bermuda as a shortwave upper trough. Relatively warmer air ahead of these upper vorticity features supports NE Atlantic upper ridge.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1031 mb center just north of the Azores supported by southeastern convergence of paragraph P3 NE Atlnatic upper ridge. Recently the surface 1031 mb center has become vertically stacked with the upper ridge center. The south side of this surface ridge previously advected dry Saharan air from Africa as observed by low-latitude brown shading in the above thermo chart. However as also observed by the white shading in the lower-right of the above thermo chart...the stream of dry Saharan air appears to be diminishing due to the tropical wave thunderstorm activity from the southeast.

...TROPICAL BELT DISCUSSION...
P5...Upper vorticity previously in the western Caribbean has been pushed into the western Gulf of Mexico due to latent heat release associated with tropical disturbance Invest 95-L mentioned in paragraph P7. The Caribbean upper anticyclone mentioned in paragraph P6 of discussion #74 has become associated with the outflow of disturbance Invest 95-L and is currently centered over the SE Gulf of Mexico. Relatively lower pressures east of the upper anticyclone supported the formation of upper vortex over the Lesser Antilles as mentioned in paragraph P8 of discussion #74...and currently this upper vortex is centered over southern Hispaniola. To the east of the upper vortex...large eastern Atlatnic low-latitude upper ridge persists. This eastern Atlantic upper ridge is currently split by embedded axis of upper vorticity stretching from the waters NW of the Cape Verde Islands and into the Canary Islands and Morocco. This upper vorticity is a combination of Canary Islands cut-off upper trough mentioned in paragraph P3 of discussion #74 and a cut-off fragment of upper trough moving into western Europe mentioned in paragraph P2 of discussion #74.

P6...Long front extending from north-central Atlantic surface cyclone mentioned in paragraph P2 of discussion #74 left behind surface trough in the northeastern Gulf of Mexico. This system acquired the characteristics of a tropical disturbance while exhibiting thunderstorms supported by outflow of northern Gulf upper anticyclone mentioned in paragraph P2 of discussion #74...and has been mentioned in the National Hurricane Center Tropical Weather Outlook over the last couple of days. The surface trough appears to have dissipated offshore of Louisiana as of this morning in a more hositle environment of westerly vertical shear on the north side of the outflow of disturbance Invest 95-L and south side of paragraph P2 upper trough.

P7...Tropical wave has moved across the western half of the Caribbean over the last couple of days is now entering the southeastern Mexico and the Bay of Campeche while supppressed by western Gulf upper vortex mentioned in paragraph P5. While it was predicted during special update #74A that this tropical wave would not develop due to the upper vorticity....the tropical wave has triggred an extensive area of western Caribbean thunderstorms moving into the Yucatan peninsula that appear to be organizing into a surface low pressure spin located behind the tropical wave and centered over the Mexico/Belize/Guatemala border. This system has recently been upgraded to disturbance Invest 95-L on the Naval Research Laboratory site of the US Navy. If the latent heat release of the thunderstorms continue to show signs of wedging out the western Gulf upper vorticity while the spin moves over warm Bay of Campeche waters during the next 24 hours...I will be upgrading it to a special feature on this blog. Regardless of further development...expect this system to generally track west-northwest across the Bay of Campeche and into eastern Mexico over the next couple of days while steered about the southwestern quadrant of paragraph P2 1026 mb ridge.

P8...Tropical wave formerly classified as disturbance Invest 94-L several days ago when it was impressive earlier is currently approaching the Lesser Antilles while inactive in enviornment of dry Saharan air mentioned in paragraph P4. Satellite animation over the last few days suggested the east side of this tropical wave left behind a small low pressure spin west of the Cape Verde Islands that is now marked as a 1011 mb low midway between the Cape Verdes and Lesser Antilles also inactive in enviornment of dry Saharan air.

P9...Tropical wave with thunderstorms and low pressure spin has recently emerged from Africa and is currently positioned southwest of the Cape Verde Islands. Although this system is taking advantage of low shear and enhanced outflow beneath paragraph P5 eastern Atlnatic upper ridge...it is headed toward unfavorable upper winds associated with axis of upper vorticity to the northwest also mentioned in paragraph P5.

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2013 Atlantic Hurricane Season Birdseye Discussion #74A (Special Update)

By: NCHurricane2009, 11:05 AM GMT on August 22, 2013

...THURSDAY AUGUST 22 2013 7:05 AM EDT...
With the exception of the NAVGEM computer model which develops the tropical wave currently moving from the central to western Caribbean (mentioned in paragraph P8 of discussion #74)...none of the reliable computer models show tropical development in the Atlantic basin for the next few days. Considering the NAVGEM an outlier solution as the other models predict that the western Caribbean upper vorticity (mentioned in paragraph P5 of discussion #74) will be in place to prevent development and as the tropical wave does not show enough thunderstorm activity latent heat release to wedge out the upper vorticity.

It appears the Atlantic tropics are in a general pattern where dry Saharan air advected from Africa is preventing tropical waves from developing. Moroever...the mid-latitude upper troughs and surface frontal systems are too far north of sufficiently warm waters for any subtropical or tropical development. Therefore I am currently suspending my daily full discussions until tropical activity potential returns to the Atlantic.

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2013 Atlantic Hurricane Season Birdseye Discussion #74

By: NCHurricane2009, 7:57 AM GMT on August 21, 2013

...WEDNESDAY AUGUST 21 2013 3:57 AM EDT...
Atlantic tropics remain quiet even as we push into the later part of August. However...compared against the 1966 to 2009 climatology...the 2013 season is ahead of schedule with the number of tropical storms (http://www.nhc.noaa.gov/climo/images/cum-average_ Atl_1966-2009.gif). But it is also worth noting this season is behind the number of average hurricanes by this date.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_21_2013_0115Z_zpsc4d1b9f0.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0123Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_21_2013_0115Z_zps970e5359.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Next upper trough and associated surface frontal cyclone in the mid-latitude westerlies is entering the upper-left corner of the above charts from Canada's Hudson Bay.

P2...Shortwave upper trough and associated surface frontal cyclone previously in the high seas SSE of Greenland is now in the NE Atlantic moving into western Europe. The shortwave upper trough previously supporting surface frontal cyclone offshore of the NE US is moving into the north-central Atlantic while the cyclone deepens to 1003 mb...but the bulk of this shortwave continues to be associated with cool air advection behind frontal cyclone that has moved across southern Greenland. It is interesting to observe the 1003 mb frontal cyclone continues to produce strong thunderstorms...but this activity is supported by non-tropical means via upper divergence ahead of the upper shortwave. Western convergence of the upper shortwave supports 1021 mb eastern US surface ridge as well as intensifying 1020 mb surface ridge that has moved into Atlantic Canada. What is left of eastern US upper trough is now upper vortex centered over Illinois and upper trough over Texas and northern Mexico. Low-level warm air ahead of the aforementioned upper shortwaves and upper vortex supports northern Gulf upper anticyclone...western Atlantic upper anticyclone...and NE Atlantic upper anticyclone shifting into western Europe.

P3...Cut-off upper trough south of the Azores has moved into the Canary Islands in advance of the easternmost shortwave upper trough moving into western Europe mentioned in paragraph P2.

P4...Surface ridge dominating much of the open Atlantic is anchored by western Atlantic 1021 mb center supported by eastern convergence of paragraph P2 western Atlantic upper anticyclone...and 1022 mb center just south of the Azores supported by northeastern convergence of paragraph P6 eastern Atlantic upper ridge. In conjunction with south side of the eastern Atlantic upper ridge...the south side of this surface ridge continues advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Upper vorticity persists from the western Caribbean and southern Florida...into the western Atlantic waters between Bermuda and Puerto Rico...extending into the tropical waters just west of the remnant of Erin.

P6...To the southeast of the upper vorticity mentioned in paragraph P5 above...large eastern Atlantic low-latitude upper ridge persists. This upper ridge has expanded into much of the Caribbean in the wake of the weakening upper vorticity.

P7...Tropical wave previously in the western Caribbean has moved into the southwestern Gulf of Mexico and has absorbed what was left of former disturbance Invest 92-L mentioned in paragraph P1 of the previous discussion.

P8...Tropical wave previously moving into the eastern Caribbean is now entering the central Caribbean waters SW of Haiti and SE of Jamiaca. During the past afternoon and earlier this evening...it produced a flare up of thunderstorms supported by outflow of paragraph P6 Caribbean upper anticyclone...and in turn latent heat release inflated the upper anticyclone such that relatively lower pressures adjacent to the inflation has supported the formation of a weak upper vortex over the Lesser Antilles. About 4 and a half days ago...this tropical wave left behind what is now the surface trough approaching the southern Lesser Antilles. Will be watching this tropical wave and surface trough to see how they interact with favorable Caribbean upper anticyclone...especially considering their was prior computer model support for the surface trough to develop as it moved in the eastern Caribbean as mentioned during the intro statements of discussions #72 and #71.

P9...Remnant low of Erin previously midway between the Cape Verde Islands and northern Lesser Antilles is moving toward the northern Lesser Antilles but has weakened further into a surface trough in a hostile environment of southwesterly shear ahead of paragraph P6 upper vorticity and dry Saharan air mentioned in paragraph P4.

P10...Tropical wave with a broad area of cyclonic turning...formerly classified as disturbance Invest 94-L when it was impressive earlier and currently located southwest of the Cape Verde Islands...has lost thunderstorm activity in the past 24 hours while ingesting dry Saharan air to the northwest mentioned in paragraph P4.

Updated: 8:00 AM GMT on August 21, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #73

By: NCHurricane2009, 2:28 AM GMT on August 20, 2013

...MONDAY AUGUST 19 2013 10:28 PM EDT...
Altantic tropics have quieted down with the remnant low of Erin weakening in a hositle environment of dry air and southerly shear (paragraph P8)...eastern Atlantic tropical wave Invest 94-L choking on a surge of dry Saharan air (paragraph P9)...and 1011 mb tropical low approaching the Lesser Antilles (paragraph P7) while all computer model support for its development has diminshed. Compared against the 1966 to 2009 climatology...as of mid-August the 2013 season is ahead of schedule with the number of tropical storms but behind schedule with the number of hurricanes (http://www.nhc.noaa.gov/climo/images/cum-average_ Atl_1966-2009.gif).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_19_2013_2215Z_zpsc56e3809.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_19_2013_2215Z_zpsf686c141.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Longwave upper trough persists across the eastern US and Atlantic high seas. As predicted during paragraph P2 of the previous discussion...the high seas portion has split into two shortwave upper troughs. The eastern of the two shortwaves supports 1003 mb frontal cyclone that has tracked from Atlantic Canada and into the high seas SSE of Greenland in the last 36 hrs. The western of the two shortwaves has supported the formation of a frontal cyclone offshore of the NE US (currently at 1009 mb)...but the bulk of this shortwave is associated with cool air advection behind frontal cyclone that has tracked from Hudson Bay (paragraph P1 of the previous discussion) and into the waters between Canada and Greenland while deepening from 999 to 991 mb in the last 36 hrs. It is interesting to observe the 1009 mb frontal cyclone offshore of the NE US is producing a strong thunderstorm cluster over waters at or greater than 26 deg C...but this thunderstorm cluster is supported by split flow upper divergence between northerlies on the east side of the NW Atlantic upper anticyclone mentioned later in this paragraph and southwesterlies ahead of the shortwave. With the upper shortwave expected to dominate the support of this system...expect it to remain non-tropical rather than transition into something more tropical. Meanwhile..western convergence of the upper trough regime formerly supported northern US surface ridge...but this ridge has been weakened and pushed south into the eastern US due to the development of aforementioned 991 mb frontal cyclone to the north (with western convergence of the 991 mb cyclone's shortwave supporting new surface 1017 mb ridge just east of Hudson Bay). Low-level warmer air ahead of the upper trough regime supports NW Atlantic upper anticyclone and NE Atlantic upper anticyclone. Remant surface trough of disturbance Invest 92-L is parked in the western Gulf of Mexico while supported by eastern divergence of the base of the upper trough located along the Texas Gulf coast.

P2...Cut-off upper vortex south of the Azores has opened into an upper trough in advance of the shortwave upper trough coming in from the northwest associated with 1003 mb frontal cyclone mentioned in paragraph P1 above.

P3...Surface ridge dominating much of the open Atlantic is anchored by western Atlantic 1022 mb center supported by southern upper convergence of paragraph P1 NW Atlantic upper anticyclone (recently this center has become vertically stacked with the anticyclone to make a deep-layered center)...and 1028 mb center just offshore of western Europe supported by eastern convergence of paragraph P1 NE Atlantic upper anticyclone. In conjunction with south side of the NE Atlantic upper anticyclone and paragraph P5 eastern Atlantic upper ridge...the south side of this surface ridge continues advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Upper vorticity persists from the western Caribbean...into the western Atlantic waters between Bermuda and Puero Rico...extending into the tropical waters just west of the remnant low of Erin. The southern Gulf upper vortex previously interacting with disturbance Invest 92-L (mentioned in paragraph P2 of the previous discussion) has merged with the western Caribbean portion of this upper vorticity.

P5...To the southeast of the upper vorticity mentioned in paragraph P4 above...large eastern Atlantic low-latitude upper ridge persists. This upper ridge has expanded into the eastern and central Caribbean in the wake of the weakening upper vorticity.

P6...Tropical wave previously in the central Caribbean has moved into the western Caribbean while suppressed by zero upper divergence directly beneath the western Caribbean upper vorticity mentioned in paragraph P5. However thunderstorms just to the north in the SE Gulf of Mexico and just to the west across the Yucatan peninsula are supported by split flow upper divergence between northeasterlies on the west side of the upper vorticity and southeasterlies rounding the SW flank of paragraph P1 NW Atlantic upper anticyclone.

P7...Tropical wave previously approaching the Lesser Antilles has crossed the islands into the eastern Caribbean. About 3 and a half days ago...this tropical wave appears to have left behind 1011 mb low further east embedded in the ITCZ which is currently nearing the Lesser Antilles. The southern half of the tropical wave and 1011 mb low are embedded in a moistening area extending across the southern half of the Caribbean supported by enhanced poleward upper outflow into paragraph P4 upper vorticty. The northern half of the tropical wave is inactive while embedded in Saharan dry air mentioned in paragraph P3.

P8...Remnant low of Erin currently midway between the Cape Verde Islands and northern Lesser Antilles continues to weaken while embedded in dry Saharan air mentioned in paragraph P3 and southerly vertical shear between upper vorticity to the west (mentioned in paragraph P4) and upper anticyclone to the east associated with a portion of paragraph P5 eastern Atlantic upper ridge.

P9...Strong tropical wave with a broad area of cyclonic turning and thunderstorms has passed south of the Cape Verde Islands and into the open tropical waters southwest of the islands. The tropical wave was previously classified as Invest 94-L while having the potential to develop in favorable environment of low shear and enhanced upper outflow below eastern Atlantic upper ridge (paragraph P5). It appears the "fly in the ointment" against development was a new surge of Saharan dry air diving southwestward from NW Africa while advected as explained in paragraph P3 above...and therefore I have cancelled this tropical wave as a special feature. The NHC has also ceased mentioning this tropical wave in thier tropical weather outlook.

Updated: 2:28 AM GMT on August 20, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #72

By: NCHurricane2009, 5:19 PM GMT on August 18, 2013

...SUNDAY AUGUST 18 2013 1:18 PM EDT...
Erin appears to be dissipating into a remnant low away from land in an environment of dry air and southerly vertical shear. See Erin special feature section for details.

Vigorous tropical wave emerging from western Africa into the tropical waters sotheast of the Cape Verde Islands has been upgraded to Invest 94-L on the Naval Research Laboratory site of the US Navy and has been introduced into the National Hurricane Center Tropical Weather Outlook. See Invest 94-L special feature section below for additional details.

Lastly...the NAVGEM computer model suggests that a 1012 mb tropical low currently located midway between the Cape Verde Islands and Lesser Antilles could develop within the next three days while approaching the eastern Caribbean Sea. Overall model support has actually reduced with the CMC model dropping this solution. In addition this system has not become better organized. Therefore I am not considering this a special feature at this time.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_18_2013_0615Z_zpsdfc69d97.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0723Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_18_2013_0615Z_zps412b5c24.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION ERIN...
While under southerly vertical shear between upper vortex to the west (mentioned in paragraph P5) and upper anticyclone to the east associated with a portion of paragraph P6 eastern Atlantic upper ridge...Erin made a northward excursion yesterday afternoon. I speculate that this excursion was due to the surface circulation getting pulled to the right by the mid-level circulation getting blasted off to the north by the southerly shear. Now that the surface circulation has decoupled from the mid-level...we are now left with a shallow tropical depression Erin which is tracking straight west this afternoon under the influence of paragraph P4 surface ridge. The shear and immersion in dry Saharan air (also mentioned in paragraph P4) have taken a toll on Erin such that we are left with a swirl of low-level clouds void of thunderstorm activity. As such...I was suprised that the NHC maintained Erin as a tropical depression during the recent 11 AM EDT advisory...but I suspect the NHC will be declaring Erin a remnant low by 5 PM EDT this afternoon. My forecast 5 PM position in Figure 1 was based on extrapolating the current westward speed of Erin easily observable on visible satellite animation. My previous discussion suggested that Erin's forward pace will slow as the steering surface ridge to the north weakens under the influence of two shortwave upper-level troughs and their associated surface lows (details on the forecast pair of shortwave upper troughs can be found in paragraph P2). Computer models in the last 24 hours have joined the Euro (ECMWF) on the second of the shortwaves being less amplifed and more progressive in forward pace such that its surface low will be incapable of pulling Erin northward. This means if Erin's remnant low lives long enough to interact with the shortwaves...we can now simply expect the current westward track to slow instead of buckling appreciably to the north.

 photo Aug_18_2013_TD_Erin_Forecast_zpsa4f498ee.png
Figure 1: My forecast versus the NHC for Tropical Depression Erin

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE INVEST 94-L...
Strong tropical wave with a broad area of cyclonic turning and thunderstorms is emerging into the waters southeast of the Cape Verde Islands. Based on where satellite shows the center of cyclonic gyration...expect this system to pass south of the Cape Verde Islands and into the open tropical Atlantic over the next few days. Models generally show a favorable environment of low shear and enhanced upper outflow below eastern Atlantic upper ridge (paragraph P6) which is why I maintain this system as a special feature. Moreover...Erin also appears to have moistened the environment ahead of this tropical wave such that it is not as likely it will interact with dry Saharan air (paragraph P4). As this tropical wave reaches the middle of the tropical Atlantic...its track could slow and potentially slow depending on how it interacts with forecast weakness in paragraph P4 surface ridge associated with Erin and pair of forecast shortwave upper trough impulses mentioned in paragraph P2.

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and associated 999 mb surface frontal cyclone has entered the upper-left of the above charts from Canada's Hudson Bay.

P2...Longwave upper trough persists across the eastern US and has been streched into the Atlantic high seas by cool air advection behind surface frontal cyclone that has rapidly moved ENE from the waters SE of Greenland and into western Europe...and another frontal cyclone that is diving SE into the Atlantic high seas from Greenland. Eastern divergence of the upper trough regime supports frontal cyclone that is departing from Atlantic Canada and into the high seas...but the center of this cyclone has weakened to a surface trough just east of Newfoundland in the last 24 hrs. This cyclone in the next 24 hrs is expected to re-develop a center further south whose cool air advection will cause the high seas portion of this longwave upper trough regime to split off into a first shortwave upper trough system that begins to weaken paragraph P4 surface ridge to the south. In the next 48 hrs...another surface frontal cyclone will develop offshore of the NE US whose cool air advection will split off a second shortwave upper trough following behind that will re-enforce the weakening of the surface ridge to the south. Western convergence of the upper trough regime supports northern US surface ridge. Low-level warmer air ahead of the upper trough regime continues to support upper ridging across the north-central Atlantic. As the base of the upper trough has amplified further south into the NW Gulf of Mexico...low-level warmer air has been washed out further south such that the associated Gulf of Mexico upper ridge has shifted into SE Mexico to the southwest of the southern Gulf upper vortex interacting with disturbance Invest 92-L. 92-L currently located in the southwest Gulf has stopped moving west under the influence of aforementioned northern US surface ridge while transitioning into a surface trough suppported by split flow upper divergence between northerlies flowing into southern Gulf upper vortex and southwesterlies ahead of the upper trough.

P3...Cut-off upper vortex persists south of the Azores. In the last 24 hrs its eastern divergence has developed a surface reflection which has become stacked below the upper vortex as a 1018 mb low.

P4...Surface ridge dominating much of the open Atlantic is anchored by 1025 mb center supported by southern upper convergence of north-central Atlantic upper ridge mentioned in paragraph P2. In conjunction with south side of this upper ridge...the south side of this surface ridge was advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. However as the above thermo chart also shows...it appears this stream of dry air has been cut-off from Africa from the southeast in association with the moisture surge from Erin and tropical wave Invest 94-L.

...TROPICAL BELT DISCUSSION...
P5...Long upper trough in the central Caribbean has retrograded into the western Caribbean while influenced by SW quad of paragraph P2 north-central Atlantic upper ridge. The Atlantic portion of this upper trough between Bermuda and Puerto Rico has merged with cut-off upper vortex west of Tropical Depression Erin mentioned in paragraph P5 of the previous discussion.

P6...To the southeast of the upper vorticity mentioned in paragraph P5 above...large eastern Atlantic low-latitude upper ridge persists. This upper ridge has expanded into the eastern Caribbean in the wake of the weakening upper vorticity.

P7...Tropical wave previously in the eastern Caribbean is moving into the central Caribbean. While the infrared imagery in the above atmo chart and water vapor imagery in the above thermo chart indicate the tropical wave is in a moistening environment supported by enhanced poleward upper outflow into paragraph P5 upper vorticity...expect the tropical wave to later become suppressed while sliding into a region of zero upper divergence directly beneath the upper vorticity.

P8...Tropical wave previously approaching the Lesser Antilles will be crossing the islands and into the eastern Caribbean later today. The wave remains inactive while embedded in Saharan dry air mentioned in paragraph P4. About 48 hrs ago...this tropical wave appears to have left behind 1012 mb low further east embedded in the ITCZ...and the thunderstorms of this surface low at times have been enhanced by poleward upper outflow into upper vorticity mentioned in paragraph P5 above. Models generally agree that this upper vorticity will weaken such that a favorable upper anticyclone builds over the 1012 mb low as it moves into the eastern Caribbean region in about 3 days time. The CMC model has ceased showing development of this 1012 mb low while the NAVGEM model continues to show development. With no signs of increasing organization and with model support declining in the last day...I am not upgrading this system to a special feature at this time.

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2013 Atlantic Hurricane Season Birdseye Discussion #71

By: NCHurricane2009, 5:00 PM GMT on August 17, 2013

...SATURDAY AUGUST 17 2013 1:00 PM EDT...
The low-levels of tropical disturbance Invest 92-L in the Gulf of Mexico appears to be insignifcant at this hour while upper-level forcing is taking over the active weather in the region. Although upper-level winds could become more favorable after 24 hours as the base of the unfavorable upper trough in this region fractures into an upper vortex retrograding westward and away...I will assume for now that 92-L will not develop and therefore I have cancelled it as a special feature on this blog. See latter part of paragraph P1 for update statement on 92-L.

Erin chugging along in the open tropical Atlantic and has a high chance of dissipating within the next five days away from land. See Erin special feature section below for details.

Impressive tropical wave is emerging from western Africa and into the tropical waters sotheast of the Cape Verde Islands. It has the potential to develop while continuing westward south of the Cape Verde Islands and into the open tropical Atlantic and therefore I am maintaining it as a special feature on this blog. See second special feature section below for additional details.

Lastly...the CMC and NAVGEM computer models suggest that a 1012 mb tropical low currently located midway between the Cape Verde Islands and Lesser Antilles could develop within the next four days while approaching the eastern Caribbean Sea. I am not considering this a special feature at this time until the system becomes better organized and or computer model support persists.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_17_2013_0015Z_zpsd74910ba.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0123Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_17_2013_0015Z_zps5aef1ccb.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM ERIN...
After weakening to a tropical depression just after my previous discussion (while moving into greater concentrations of dry Saharan air)...Erin made a comeback overnight to a tropical storm while developing a thunderstorm burst supported by split flow upper divergence between upper vortex to the west (mentioned in paragraph P5) and upper anticyclone to the east associated with a portion of paragraph P5 eastern Atlantic upper ridge. Upper-level southerlies between the upper vortex and upper anticyclone have since sheared the burst northward..and Erin looks to be weakening with the southerly shear allowing the Saharan dry air to waft its way in from the southwest. This is why I expect Erin to re-weaken to a tropical depression later today as my intensity forecast in Figure 1 shows.

While I was generating my forecast in Figure 1...visible satellite animation showed the surface circulation wobble to the north and the NHC has adjusted their center fix accordingly during their 11 AM EDT advisory. This means that Erin's actual track could end up being a tad north of both my and the 5 AM NHC forecast lines shown in Figure 1. I speculate this northward wobble was the surface circulation getting pulled to the right by the mid-level circulation getting blasted off to the north by the southerly shear. I predict we will soon have a surface circulation de-coupled from the mid-level...leaving us with a shallow low-level Erin steered by the paragraph P3 low-level ridge. Using this philosophy...in the shorter-term I agree with the NHC as shown in Figure 1 on a track that soon bends more westward while Erin no longer is tall enough to feel the poleward tug associated with the upper vortex to the west and comes entirely under the influence of the paragraph P3 low-level ridge. I become slower than the NHC forecast track by 48 hours and beyond while models agree that the low-level ridge to the north will weaken due to a shortwave upper trough breaking off from the paragraph P1 eastern US longwave. By 96 and 120 hrs...a second shortwave upper trough breaks from the longwave while driving a more substantial surface low. The Euro (ECMWF) is most progressive with the second shortwave such that by 120 hrs its surface low is entirely to the northeast of Erin with the pargraph P3 surface ridge re-developing to the north and offshore of Atlantic Canada. The GFS is least progressive and amplifies the shortwave such that the surface low grows big enough to pull Erin due northward by 120 hrs. The NAVGEM and CMC are somewhere in between the ECMWF and GFS extremes...having the surface low split into one weak area north of Erin and another in the NE Atlantic. For now...I am going with the middle-ground between ECMWF and GFS to suggest a system taking a slow northwest track toward a weak surface low to the north by 120 hrs (the track would be slow as Erin would be in conflicting steering between eastern and western cells of the low-level ridge due to the weak nature of such a surface low).

Intensity-wise...my forecast track keeps Erin in a hostile environment of southwesterly shear to the east of the westward-retrograding upper vortex mentioned in paragraph P5 and dry Saharan air mentioned in paragraph P3. I will assume that the shear will be low enough and that Erin will stay in touch with the outflow of the upper anticyclone to the east such that I keep her hanging on at tropical depression status for much of the forecast period. If my day 5 (5 AM Thu) position in Figure 1 is correct...Erin should become embedded in more intense southwesterly shear as the second shortwave upper trough passing by to the north reverses the upper vortex's track eastward into Erin. This is when I currently forecast Erin to dissipate.

 photo Aug_17_2013_TS_Erin_Forecast_zps29039d46.png
Figure 1: My forecast versus the NHC for Tropical Storm Erin

Impact swath in Figure 1 begins with tropical storm wind radius shown by NHC...and then dissipating that wind radius later today as I expect Erin to weaken to a tropical depression.

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Strong tropical wave with a broad area of cyclonic turning and thunderstorms is emerging into the waters sotheast of the Cape Verde Islands. Based on where satellite shows the center of cyclonic gyration...expect this system to pass south of the Cape Verde Islands and into the open tropical Atlantic over the next few days. Models generally show a favorable environment of low shear and enhanced upper outflow below eastern Atlantic upper ridge (paragraph P5) which is why I maintain this system as a special feature. Moreover...Erin also appears to have moistened the environment ahead of this tropical wave such that it is not as likely it will interact with dry Saharan air (paragraph P3). As this tropical wave reaches the middle of the tropical Atlantic...its track could slow and potentially bend more poleward depending on how it interacts with forecast weakness in paragraph P3 surface ridge associated with Erin and weak surface low expected to develop north of Erin.

...MID-LATITUDES DISCUSSION...
P1...Large-sized upper trough anamalous for the month of August remains amplified across the eastern US and is being streched into the Atlantic high seas in the vicinity of southern Greenland by cool air advection behind surface frontal cyclone that has rapidly moved NE from Atlantic Canada and into the waters SE of Greenland. This frontal cyclone is generally supported by eastern divergence of this upper trough regime. This divergence also supports frontal cyclone that has moved from Canada's Hudson Bay and into Atlantic Canada (marked as 1019 mb in the above atmo chart). Western convergence of the upper trough supports northern US surface ridge extending to a 1025 mb center offshore of Atlantic Canada. Low-level warmer air ahad of the upper trough regime continues to support upper ridging across the north-central and northeast Atlantic. As the base of the upper trough has amplified further south into eastern Texas...low-level warmer air has been washed out further south such that the associated southern US upper ridge has moved southward across the Gulf of Mexico while hugging the southern Gulf upper vortex interacting with disturbance Invest 92-L and while merging with the former upper anticyclone associated with 92-L. We now have a plume of tropical moisture across the Gulf of Mexico and southeastern US...the south end of which is supported by split flow upper divergence between northerlies flowing into southern Gulf upper vortex and southwesterlies ahead of the upper trough...and the rest of which is supported by eastern divergence of the upper trough regime. Meanwhile...the surface spin of 92-L continues west into the southwestern Gulf while a shallow feature steered by south side of aforementioned northern US surface ridge instead of transitioning into a northward-tracking low pressure supported by the eastern divergence of the upper trough regime as previously forecast.

P2...Cut-off upper vortex persists southeast of the Azores. Associated surface trough has dissipated.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1028 mb center supported by southeastern upper convergence of north-central Atlantic upper ridge mentioned in paragraph P1. In conjunction with south side of this upper ridge...the south side of this surface ridge was advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. However as the above thermo chart also shows...it appears this stream of dry air has been cut-off from Africa from the southeast in association with the moisture surge from Tropical Storm Erin and our special feature tropical wave behind Erin.

...TROPICAL BELT DISCUSSION...
P4...Long upper trough persists in the central Caribbean and western waters between Bermuda and Puerto Rico.

P5...To the east of the upper trough mentioned in paragraph P4 above...large eastern Atlantic low-latitude upper ridge persists. Within this upper ridge is a westward-retrograding upper vortex located west of Tropical Storm Erin.

P6...Tropical wave previosly just east of the Lesser Antilles is now in the eastern Caribbean Sea. It is currenlty inactive while embedded in paragraph P3 dry Saharan air layer...and looks to remain inactive while sliding into a region of zero upper divergence beneath paragraph P4 upper trough.

P7...Tropical wave previously midway between the Cape verde Islands and Lesser Antilles is now approaching the Lesser Antilles and remains inactive while embedded in Saharan dry air mentioned in paragraph P3. It appears this tropical wave has left behind a 1012 mb low further east embedded in the ITCZ...and the thunderstorms of this surface low are currently enhanced by poleward upper outflow into upper vortex (this is the same upper vortex west of Erin mentioned in paragraph P5). Models generally agree that the upper vortex and paragraph P4 upper trough will merge to the northwest of the 1012 mb low...but then weaken such that a favorable upper anticyclone builds over the 1012 mb low as it moves into the eastern Caribbean region in about 4 days time. In fact...the NAVGEM and CMC suggest development potential from this low and therefore will be keeping a watch on this feature.

Updated: 2:48 PM GMT on August 18, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #70

By: NCHurricane2009, 11:28 AM GMT on August 16, 2013

...FRIDAY AUGUST 16 2013 7:30 AM EDT...
It appears further development of tropical disturbance Invest 92-L has become less likely as it moves into the southern Gulf of Mexico. I have maintained it as a special feature for now...but may issue a special update later today to cancel it as one. Interests along the south-facing United States Gulf coast should still continue to monitor this situation. See Invest 92-L special feature section below for additional details.

Tropical depression five in the eastern Atlantic has become Tropical Storm Erin. Erin is likely to face a poor future while heading into an unfavorable picture from a thermodynamic perspective. See Erin special feature section below for additional details.

An impressive tropical wave over western Africa has the potential to develop to the east of Tropical Storm Erin when it emerges into the Atlantic. Therefore I have upgraded it to a special feature even though it has yet to enter the scope of any of the below charts. See third special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_16_2013_0015Z_zpsa7713573.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 0122Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_16_2013_0015Z_zps747ae360.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...SOUTHERN GULF OF MEXICO DISTURBANCE INVEST 92-L...
Western Caribbean tropical wave and associated cyclonically turning thunderstorms have moved into the Yucatan peninsula and southern Gulf of Mexico regions while sliding below southern Gulf of Mexico upper vorticity. The upper vorticity has the structure predicted in the August 14 18Z GFS model run discussed previously...and that model run did not develop this system. Indeed this system is not quiet as impressive as the surface vorticity is stacked below the southern Gulf upper vorticity...leaving the cyclonically turning thunderstorms and associated upper anticyclone to be biased east of the surface vorticity. However based on some of the current model runs that still show a weakly-developing system...expect in the next 24 hrs the southern Gulf upper vorticity to get pushed southwestward by southward-moving southern US upper ridge (paragraph P1) fragment. This upper ridge gets pushed southward due to amplifying shortwave upper trough associated with longwave eastern US upper trough (paragraph P1)...with Invest 92-L's surface vorticity evolving into a northward-tracking low pressure system supported by eastern divergence of the upper trough (but behaving a mostly-tropical to semi-tropical system while retaining outflow with its eastern upper anticyclone). In such a sceanrio...this system would be crossing the south-facing US Gulf coast in about 48 hours (2 days).

...SPECIAL FEATURE...TROPICAL STORM ERIN...
Thunderstorm activity remains genearlly biased to the south half of the circulation perhaps due to the marginal water temps below 26 deg C just to the north and perhaps due to a tinge of dryness from the paragraph P3 Saharan air layer to the northwest. Due to the fact that the system's thunderstorms are not impressive per latest colorized infrared satellite...my updated forecast in Figure 1 shows no additional strengthening...followed by weakening beginning on Saturday (as I previously showed) due to the system reaching greater concentrations of dry Saharan air shown in the above thermo chart. The NHC recorded storm track shown in Figure 1 represents the first 24 hours of this system's life as a tropical cyclone...and based on extrapolating that forward pace I am a bit faster than the NHC forecast initially. I agree with slowing down my forecast track and matching the NHC's forward pace after 72 hrs as this is when models show the paragraph P3 surface ridge to the north weakening a bit. Due to the angle of the NHC recorded storm track...I also agree with the NHC's strategy of a northward adjustment compared to 24 hrs ago...but I am not quiet as far to the north as NHC as the angle of the recorded storm track does not quiet match the NHC's forecast track angle (therefore I have a southward bias thru the forecast period). The troipcal cyclone is currently vertically coupled enough to feel some poleward tug from cut-off upper vortex to the west mentioned in paragraph P5...and just as I have done previously I bend the track westward on Saturday due to the expected weakening (hence becoming shallower and decoupled from upper-level poleward tug). It should be noted that my day 5 position (11 PM Tue) would place Erin in hostile southwesterly vertical shear on the southeast quad of the upper vortex to her west (based on the 120 hr position of the upper vortex in the latest GFS model run)...which could mean Erin maybe dissipating by 120 hrs.

 photo Aug_16_2013_TS_Erin_Forecast_zpsf09f8d7c.png
Figure 1: My forecast versus the NHC for Tropical Storm Erin

Impact swath in Figure 1 begins with tropical storm wind radius shown by NHC...and then dissipating that wind radius about the time I think Erin will weaken to a tropical depression.

...SPECIAL FEATURE...WESTERN AFRICA TROPICAL WAVE...
A strong tropical wave with an impressive thunderstorm mass is currently over inland western Africa and not yet in the scope of the above charts. However I have already made it a special feature as their has been some model support for this system quickly developing in favorable low shear and enhanced upper outflow below eastern Atlantic upper ridge (paragraph P5) at a location well to the east of Erin as it emerges into the Atlantic. Erin also appears to have moistened the environment ahead of this tropical wave such that it is not as likely it will interact with dry Saharan air (paragraph P3) as it moves off the African coast. Due to uncertainty on precisely where this system would spin up a surface center...interest in the Cape Verde Islands should monitor this tropical wave.

...MID-LATITUDES DISCUSSION...
P1...Frontal cyclone and attendant north-central Atlantic upper trough passing by southern Greenland is moving into the northeast Atlantic and western Europe. Meanwhile...large-sized upper trough anamalous for the month of August remains amplified across the eastern US to the east of a western North America upper ridge. Eastern divergence of this upper trough regime supports frontal cyclone that has depeened to 995 mb while moving NE across Atlantic Canada...and supports 1010 mb frontal cyclone that has dove in from Canada's Hudson Bay. Local maximums of cool air advection behind each cyclone have created small upper vortices within the upper trough. Western convergence of the upper trough supports 1021 mb surface ridge over the central US. Low-level warm air south of the aforementioned 1010 and 995 mb frontal cyclones supports southern US upper ridge which has spread northeastward into the north-central and northeastern Atlantic due to southwesterly advection of the warm air ahead of the frontal cyclones.

P2...Cut-off upper vortex and associated surface low southeast of the Azores persists. The surface low has recently weakened to a surface trough.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1026 mb center supported by southeastern upper convergence of north-central Atlantic upper ridge mentioned in paragraph P1. In conjunction with south side of aforementioned north-central Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Cut-off upper vortex southeast of Bermuda (paragraph P4 of the prior discussion)...eastern Caribbean upper trough (paragraph P6 of prior discussion)...and inverted upper trough moving into the Lesser Antilles (paragraph P5 of the prior discussion)...have merged into a long upper trough currently spanning the central Caribbean and west Atlantic waters between Bermuda and Puerto Rico.

P5...The upper anticyclone of Invest 92-L remains split from larger eastern Atlantic upper ridge by paragraph P4 upper trough. Within the east Atlantic upper ridge...the prior inverted upper trough west of the Cape Verde Islands has merged with southern fracture of paragraph P2 upper vortex...resutling in a westward-retrograding upper vortex west of Tropical Storm Erin that has been expected.

P6...Within the last 24 hours...the NHC TAFB has declared a tropical wave that was apparently previously poorly-defined. The wave was positioned just east of the Lesser Antilles. Will have to later re-analyze the date when this wave emerged from Africa. This tropical wave is currenlty inactive while embedded in paragraph P3 dry Saharan air layer.

P7...Tropical wave midway between the Cape verde Islands and Lesser Antilles continues to have limited thunderstorm activity while embedded in dry Saharan air mentioned in paragraph P3.

Updated: 2:49 PM GMT on August 18, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #69A (Special Update)

By: NCHurricane2009, 4:37 AM GMT on August 15, 2013

...THURSDAY AUGUST 15 2013 12:30 AM EDT...
Strong tropical wave in the eastern tropical Atlantic...previously designated as Invest 93-L...has intensified into the fifth tropical depression of the 2013 Atlantic hurricane season. My forecast versus the NHC's is detailed in Figure 1 below. In the meantime...return to full discussion #69 for an assessment on the rest of the Atlantic tropics including the threat of tropical cyclone formation in the northwestern Caribbean and southern Gulf of Mexico regions from Invest 92-L. Visit www.nhc.noaa.gov for up to the minute latest information on tropical depression five and latest developments associated with Invest 92-L.

 photo Aug_14_2013_TD_Five_Forecast_zps89fcfd04.png
Figure 1: My forecast versus the NHC for Tropical Depression Five

Concerning tropical depression five...the thunderstorm activity is biased to the south half of the circulation perhaps due to the marginal water temps below 26 deg C just to the north and perhaps due to a tinge of dryness from the Saharan air layer to the northwest. I show an only-gradual strengthening trend to a moderate tropical storm for the next 36 hrs as it will be adjacent to this pool of marginal water temps based on the track forecast. Beginning in 36 hrs...based on the thermo chart shown in discussion #69 and the track forecast...the tropical cyclone should begin encountering higher concentrations of Saharan dry air while simultaneoulsy moving away from adjacent pool of marginal waters. For now I am assuming after 36 hrs that this dry air will win out over the warmer waters and hence gradually weaken the system back to a tropical depression especially since models are not gung-ho about developing this system in the long range. Forward pace of NHC track forecast is in agreement with the 6-hourly motion witnessed on satellite between 5 and 11 PM EDT Wednesday. And with the expectation that the cyclone should strengthen a bit in the short term and hence become vertically coupled enough to feel some poleward tug from developing cut-off upper vortex to its northwest...I agree with the WNW track shown by NHC for the first 48 hours. While I agree with the westward bend in track (as the cyclone becomes shallower/weaker and hence decoupled from upper-level poleward tug)...I go a bit faster than the forward pace of NHC between 48 and 72 hrs as the GFS model shows the paragraph P3 surface ridge maintaining strength in that time. I then agree with the NHC's slowdown in forward pace after 72 hrs as this is when the GFS model shows the paragraph P3 surface ridge weakening a bit.

Impact swath begins with the development of a tropical storm wind field just south of center as the tropical cyclone currently has its thunderstorm activity biased to the south due to the marginal water temps to its north. When studying the GFS upper wind forecast relative to the forecast track in Figure 1...it seems that after 24 hours the system will reach some light southerly vertical shear on the east side of the westward-retrograding upper vortex. Even though the thermodynamics thru the forecast period generally suggest the thunderstorms should stay biased to the south (due to either marginal waters to the north or dry Saharan air to the northwest)...I expect the southerly shear to somewhat counteract that and make the strongest thunderstorms more symmetric about the center...which is why after 24 hrs my impact swath becomes more symmetric about the storm track. Impact swath dwindles late in the forecast to simulate my current projection of the system weakening back to a tropical depression later on. Tropical storm warnings are currently in effect for the southern Cape Verde Islands. Based on my impact swath...I personally predict that the islands have a near-zero percent chance of actually realizing tropical storm sustained winds.

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2013 Atlantic Hurricane Season Birdseye Discussion #69

By: NCHurricane2009, 2:53 AM GMT on August 15, 2013

...WEDNESDAY AUGUST 14 2013 10:53 PM EDT...
Atlantic tropics remain at escalated levels as we push into the second half of August with three current areas of active weather. Two of these areas...designated as disturbances Invest 92-L and 93-L...are on the brink of becoming tropical cyclones at any time.

High probability of tropical cyclogensis in the northwestern Caribbean and or southern Gulf of Mexico in the next 24 hours. Interests in the northwestern Caribbean Sea...western Cuba...Yucatan Peninsula...Gulf of Mexico...and along the United States Gulf coast from Louisiana to the Florida panhandle should monitor this situation carefully. See Invest 92-L special feature section below for additional details.

Upper vortex southeast of Bermuda continues producing active weather as mentioned in paragraph P4...but is not expected to develop into a subtropical cyclone due to high surface pressures in the area.

Vigorous and well-organized tropical wave in the eastern Atlantic is very close to tropical cyclone status as it begins passing south of the Cape Verde Islands tonight. Based on the upper wind forecasts becoming more favorable...I have upgraded this system to a special feature. See Invest 93-L special feature section below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_14_2013_2045Z_zps04b7eb00.png<
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1319Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_14_2013_2045Z_zpsed50bfce.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...CARIBBEAN TROPICAL WAVE INVEST 92-L...
Western Caribbean tropical wave and associated cyclonically turning thunderstorms has become very well organized in the last 24 hours. This is a classic case of gradual tropical development where an extensive thunderstorm region supported by surface convergence of a surface low pressure feature (in this case the tropical wave) pumps up an upper anticyclone via latent heat release...and in turn the upper outflow of the upper anticyclone supports additional surface pressure falls. I continue to forecast this system will become a tropical cyclone in the timeframe that is currently the next 24 hours as it moves into the Yucatan Peninsula/southern Gulf of Mexico region. I then currently favor the NAVGEM middle-of-the-ground solution described below which would suggest a mostly tropical system making landfall along the south-facing US Gulf coast in about 72 hours.

 photo Aug_14_2013_300mb_GFS_for_Invests_92L_and_93L_zps4878113f.png
Figure 1: GFS upper-level (300 mb) wind forecast trends between yesterday (18Z Aug 13) and tonight (18Z Aug 14). The change in the upper wind forecasts annotated above is less favorable for Invest 92-L and more favorable for Invest 93-L.

Despite the impressive nature of this system...the GFS computer model run has decided to stop showing development...the prognosis given in Figure 1 above. In short...Figure 1 shows the GFS no longer pushing the paragraph P5 southern Gulf of Mexico upper vortex westward and out of the way such that the upper vortex shears apart this system in the next 24 hours. For now I am assuming the GFS is incorrect while potentially underplaying the currently impressive nature of the upper anticyclone which I still think is capable of pushing out the upper vortex. I will note that the thunderstorm intensity has been on the decline since this afternoon...and if thunderstorms do not recover later tonight to pump up the upper anticyclone with additional latent heat release...then maybe the GFS is on to something and I may have to issue a special update before my next blog post to cancel this system as a special feature.

Meanwhile...the current NAVGEM model run shows a moderate solution where the upper anticyclone pushes the upper vortex westward into the western Gulf where it then merges with southwestern lobe of paragraph P1 eastern US upper trough such that we have the development of a western Gulf upper trough. While the development of an upper trough normally signifies unfavorable westerly shear...in this scenario the upper trough is highly amplfied at a location west of the system's strong upper anticyclone (and a more amplified upper trough means less westerly shear)...and the upper anticyclone in this scenario covers the eastern two-thirds of this system such that shear should be light enough for additional development. This upper wind configuration suggests that this system will have eastern anticyclonic outflow as in a tropical system while simultaneously behaving as a northward-tracking low pressure system supported by eastern divergence of the upper trough as in a non-tropical system. Therefore the system in this scenario would be making landfall along the south-facing US Gulf coast in about 72 hours (3 days) as a vigorous mostly-tropical to semi-tropical system.

The current CMC solution is an extreme one whereby the upper anticyclone is strong enough to entirely squash out the southern Gulf upper vortex and keep the paragraph P1 eastern US upper trough at bay to the north such that we have a strong tropical cyclone tracking west-northwest across the southwestern Gulf of Mexico generally steered by the paragraph P1 central US surface ridge. Because CMC historically overdoes tropical cyclones....I am not considering this solution.

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE INVEST 93-L...
While taking advantage of low shear and enhanced upper outflow beneath the eastern Atlantic low-latitude upper ridge mentioned in paragraph P5...the eastern Atlantic tropical wave continues to become better organized while on its way to pass south of the Cape Verde Islands tonight. The thunderstorm activity is biased to the south half of the low pressure spin perhaps due to the marginal water temps below 26 deg C just to the north and perhaps due to a tinge of dryness from the Saharan air layer to the northwest mentioned in paragraph P3. As the end of paragraph P5 mentions...two upper troughs due west of this system are beginning to merge in what will become a westward-retrograding upper vortex. Previous dilemna was that this westward-tracking system had the potential to phase with the southeast side of this upper vortex such that it would be supressed by southwesterly vertical shear. Based on the GFS computer model trend between yesterday and tonight shown in Figure 1 above...it appears that the southeast extent of this upper vortex will be weaker than previously thought perhaps due to the tremendous latent heat release of this system's sprawling field of thunderstorms. Coupled with the fact that GFS...CMC...Euro...and NAVGEM more or less continue to suggest additional development...I am more convinced of tropical cyclogenesis and have upgraded this system to a special feature.

With the system forecast to generally track westward while steered by south side of paragraph P3 ridge...it will be heading toward warmer sea-surface temperatures as shown by the above thermo chart. Coupled with the fact that the forecast retrograding upper vortex is no longer expected to unfavorably affect this system...it seems conditions are potentially ripe for a strong tropical cyclone. However some of the longer-range computer model runs weaken this system as it approaches the Lesser Antilles...perhaps due to the higher concentration of paragraph P3 Saharan dry air to the west as seen in the above thermo chart. For instance the tropical wave ahead of this system...mentioned in paragraph P7 below...has been gradually losing its thunderstorms while running into the greater concentration of Saharan air. We shall se...stay tuned with this system over the next few days...

...MID-LATITUDES DISCUSSION...
P1...992 mb frontal cyclone passing by the south tip of Greenland has deepened a bit to 987 mb within the last 24 hrs while tapping into eastern divergence of associated north-central Atlantic upper trough. The north-central Atlantic upper trough four days ago left behind upper trough which continues amplifying southward across the eastern US to the east of a developing western North America upper ridge. Eastern divergence of this upper trough supports surface frontal depression that has deepened from 1006 to 1005 mb in the last 24 hrs while moving into Atlantic Canada from the NE US...and the upper trough is being re-enforced by cool air advection behind 1000 mb frontal cyclone diving in from Canada's Hudson Bay. Western convergence of the upper trough supports 1024 mb surface ridge over the central US. Low-level warm air south of the aforementioned 1005 and 987 mb frontal cyclones supports southern US upper ridge which has spread northeastward into the north-central and northeastern Atlantic due to southwesterly advection of the warm air ahead of the frontal cyclones.

P2...Cut-off Azores upper vortex has been pushed southeastward into the waters west of the Canary Islands due to amplification of north-central Atlantic upper ridge mentioned in paragraph P1. Associated surface trough formerly supported by eastern divergence of this upper vortex has become a 1017 mb low stacked directly below the upper vortex.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1026 mb center supported by southeastern upper convergence of north-central Atlantic upper ridge mentioned in paragraph P1. In conjunction with south side of aforementioned north-central Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. However this dry air appears to be mitigated from the southeast by the thunderstorm activity associated with the strong tropical waves mentioned in paragraph P7 and in the Invest 93-L special feature section.

...TROPICAL BELT DISCUSSION...
P4...Cut-off upper vortex persists southeast of Bermuda. The west and south sides of this upper vortex continues to produce an area of thunderstorms supported by split flow upper divergence at the boundary between the upper vortex and paragraph P1 southern US/north-central Atlantic upper ridge. All surface troughing below the upper vortex has dissipated due to the high surface pressures associated with paragraph P3 open Atlantic surface ridge...and therefore am no longer monitoring this area for potential subtropical cyclone development.

P5...Southern Gulf upper vortex has weakened into a southwest-northeast oriented upper trough while becoming squashed between paragraph P1 southern US upper ridge and intensifying upper anticyclone over our special feature Invest 92-L coming in from the southeast. The upper anticyclone of Invest 92-L remains split from larger eastern Atlantic upper ridge by paragraph P4 upper vortex SE of Bermuda. Prior inverted upper trough midway between the Lesser Antilles and Cape Verde Islands is retrograding westward into the Lesser Antilles...and prior inverted upper trough west of the Cape Verde Islands is beginning to merge with southern fracture of paragraph P2 upper vortex (which is currently a central Atlantic east-west upper trough).

P6...Eastern Caribbean tropical wave has dissipated as of the 0600Z NHC TAFB analysis below suppressive non-divergent upper air environment associated with new eastern Caribbean inverted upper trough that has developed in relatively lower pressures east of the intensifying upper anticyclone of disturbance Invest 92-L.

P7...Tropical wave midway between the Cape verde Islands and Lesser Antilles continues to have limited thunderstorm activity while embedded in dry Saharan air mentioned in paragraph P3.

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2013 Atlantic Hurricane Season Birdseye Discussion #68

By: NCHurricane2009, 11:14 AM GMT on August 14, 2013

...WEDNESDAY AUGUST 14 2013 7:14 AM EDT...
Atlantic tropics are heating up for the second half of August with three current areas of active weather...

High probability of tropical cyclogensis in the norhtwestern Caribbean and or Gulf of Mexico in the next 48 hours. Interests in the northwestern Caribbean Sea...western Cuba...Yucatan Peninsula...Gulf of Mexico...and along the United States Gulf coast from Louisiana to the Florida panhandle should monitor this situation carefully. See special feature section below for additional details.

Upper vortex southeast of Bermuda continues producing active weather as mentioned in paragraph P4. Although their is currently no computer model support for additional development...will be watching this system for potential subtropical cyclone development. So far it appears surface pressures are too high for additional development and therefore I continue to not upgrade it to a special feature.

A vigorous and well-organized tropical wave is emerging into the eastern Atlantic from western Africa. Although their is high computer model support for additional development as it moves westward across the Atlantic tropics...I have not upgraded it to a special feature based on the upper wind forecast for the long term. However should this rapidly organizing tropical wave show imminent signs of rapid tropical cylcogenesis in the short term later today...I will issue special updates between now and my next blog post. See paragraph P8 below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_13_2013_2045Z_zps5f03e088.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_13_2013_2045Z_zpsb055e4a1.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...CARIBBEAN TROPICAL WAVE INVEST 92-L...
Eastern Caribbean surface trough has moved into the central and western Caribbean regions while becoming slowly more organized in an extensive field of active thunderstorms. The surface trough has been upgraded to a tropical wave within the last day...and so we will have to do some re-analysis later to figure out when exactly this tropical wave had emerged from Africa. In the meantime...this is a classic case of gradual tropical development where an extensive thunderstorm region supported by surface convergence of a surface low pressure feature (in this case the tropical wave) pumps up an upper anticyclone via latent heat release...and in turn the upper outflow of the upper anticyclone supports additional surface pressure falls. This area of disturbed weather within the last 24 hours has been upgraded to Invest 92-L on the Naval Reaserch Laboratory site of the US Navy.

Based on the similar solutions shown by last night's 18z cycle of GFS...CMC...and NAVGEM models...I forecast this system will slowly organize into a tropical cyclone as it moves into the Yucatan Peninsula/southern Gulf of Mexico region in the next 48 hours. It is about this time that models consistently show the eastern US upper trough mentioned in paragraph P1 merge with the southern Gulf upper vortex mentioned in paragraph P5. While the development of an upper trough normally signifies unfavorable westerly shear...this upper trough is expected to be highly amplfied at a location west of the system's strong upper anticyclone (and a more amplified upper trough means less westerly shear)...and the upper anticyclone is expected to at least cover the eastern two-thirds of this system such that shear should be light enough for additional development. This upper wind configuration also suggests that this system will have eastern anticyclonic outflow as in a tropical system while simultaneously behaving as a northward-tracking low pressure system supported by eastern divergence of the upper trough as in a non-tropical system. Therefore as this system makes landfall along the south-facing US Gulf coast in about 96 hours (4 days)...this system will likely be a vigorous mostly-tropical to semi-tropical system.

...MID-LATITUDES DISCUSSION...
P1...985 mb frontal cyclone between Canada and the Atlantic high seas has weakened to 992 mb in the last 24 hrs directly below the non-divergent center of its upper vortex while passing by the south tip of Greenland...and the upper vortex has recently opened into a large north-central Atlantic upper trough. The upper vortex three days ago left behind upper trough which continues amplifying southward into the eastern US to the east of a developing western North America upper ridge. Eastern divergence of this upper trough supports surface frontal depression that has deepened from 1012 to 1006 mb in the last 24 hrs while moving from the Great Lakes to the NE US. Western convergence of the upper trough supports strong 1028 mb surface ridge over the north-central US and central Canada. Low-level warm air south of the aforementioned 1006 and 992 mb frontal cyclones supports southern US upper ridge which has spread eastward into the western Atlantic and northeastward into the northeast Atlantic due to westerly and southerly advection of the warm air ahead of the frontal cyclones.

P2...Azores upper vortex continues to be cut-off due to amplifying northeast Atlantic upper ridge mentioned in paragraph P1. Associated 1020 mb frontal depression north of the Azores mentioned in the previous discussion has dissipated...and what is left of its front is a weak surface trough just west of the Canary Islands supported by eastern divergence of the upper vortex.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1027 mb center NE of the Azores supported by southeastern upper convergence of northeast Atlantic upper ridge mentioned in paragraph P1. This surface ridge has a westward 1018 mb extension into the northern Gulf of Mexico supported by southeastern convergence of southern US/W Atlantic upper ridge mentioned in paragraph P1. In conjunction with south side of aforementioned northeast Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart. However this dry air appears to be mitigated from the southeast by the thunderstorm activity associated with the strong tropical waves mentioned in paragraphs P7 and P8.

...TROPICAL BELT DISCUSSION...
P4...Cut-off upper vortex persists southeast of Bermuda. The west and south sides of this upper vortex continues to produce an organized curved band of thunderstorm activity supported by split flow upper divergence at the boundary between the upper vortex and paragraph P1 southern US/W Atlantic upper ridge (a new surface trough south of Bermuda has been marked in recent NHC TAFB maps...and surface trouhging below these thunderstorms also appears re-enforced by the decaying south end of the front associated with paragraph P1 992 mb cyclone). Eastern divergence of this upper vortex also continues supporting an eastern surface trough. Paragraph P1 eastern US upper trough is expected to create weakness in the vicinity of Bermuda in the aforementioned upper ridge...and whatever surface features associated with upper vortex look to get trapped between paragraph P3 Atlantic surface ridge and paragraph P1 north-central US/central Canada surface ridge coming in from the west. Therefore in the next 48 hrs...this system looks to stall out after it retrogades to a location south of Bermuda. Due to the abundance of perhiperial upper divergence around the upper vortex and potential instability of the cold air of the upper vortex relative to warm 29 to 30 deg C waters...am watching this area for potential subtropical development even though their is no current computer model support. So far it apperas high surface pressures associated with paragraph P3 Atlantic surface ridge have stifled additional development.

P5...Southern Gulf upper vortex persists. To the southeast of the upper vortex...Central America upper ridge and eastern Caribbean upper anticyclone have merged into one large upper anticyclone that has become the upper outflow structure of our special feature Invest 92-L. The upper anticyclone of Invest 92-L remains split from larger eastern Atlantic upper ridge by paragraph P4 upper vortex SE of Bermuda. Prior inverted upper trough midway between the Lesser Antilles and Cape Verde Islands is retrograding west...and a new inverted upper trough apperas to be developing just west of the Cape Verde Islands in relatively lower pressures adjacent to the inflation of the far eastern portion of this upper ridge in association with the thunderstorm latent heat release associated with tropcal wave Invest 93-L mentioned in paragraph P8 below.

P6...Tropical wave has crossed the Lesser Antilles into the eastern Caribbean. Although it has escaped the dry Saharan air mentioned in paragraph P3...additional development is unlikely as the surface levels will be dominated by low pressure field of our special feature Invest 92-L to the west and the upper levels will be dominated by unfavorable northerly vertical shear on the east side of the upper anticyclone of Invest 92-L.

P7...Tropical wave previously west of the Cape Verde Islands is now midway between the Cape verdes and Lesser Antilles and continues to have a 1010 mb surface low pressure spin. However the associated thunderstorm activity conintues to be on the decline while ingesting dry Saharan air mentioned in paragraph P3.

P8...By moistening the air ahead against the paragraph P3 dry Saharan air layer...it appears the tropical wave in paragraph P7 has become the sacrificial system for new and already rapidly-organizing tropical wave emerging from Africa into the waters southeast of the Cape Verde Islands. The organization has been so rapid that it has already been desiganted as Invest 93-L and has been given a moderate chance for tropical cyclogensis by the NHC tropical weather outlook even though this system has been in the outlook for less than 24 hrs as of this writing. Last night's 18Z cycle of GFS...NAVGEM...Euro (ECMWF)...and CMC agreed on additional development of this system. However I am not absolutely certain on tropical cyclogenesis in this case and therefore have not upgraded it to a special feature. This is because upper-level wind forecasts consistently show the south end of paragraph P2 upper vortex fracturing into a westward-retrograding unfavorable upper vortex within the next 24 hrs. If this westward-tracking tropical wave phases with the upper vortex's southeast side and or directly below the upper vortex....this could mean extensive southwesterly vertical shear and or suppression directly below its non-divergent center. I was also skeptical of the model runs that develop this tropical wave as they show too slow of a westward track with the wave itself such that it stays east of the unfavorable effects of the upper vortex (for instance the models show the wave passing south of the Cape Verde Islands in the 36 to 48 hr timeframe when realisticaly satellite shows the wave should be passing south of the islands by 24 hrs). However should this rapidly organizing tropical wave show imminent signs of rapid tropical cylcogenesis in the short term later today...I will issue special updates between now and my next blog post.

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2013 Atlantic Hurricane Season Birdseye Discussion #67

By: NCHurricane2009, 5:03 AM GMT on August 13, 2013

...TUESDAY AUGUST 13 2013 1:03 AM EDT...
Computer model support persists for tropical cyclone formation in the northwest Caribbean and or Gulf of Mexico beginning in the timeframe that is 4 days from now. I previously assessed this was associated with the tropical wave currently approaching the Lesser Antilles (paragraph P7). However it appears this is more associated with a relatively new eastern Caribbean surface trough. Interests in the northwestern Caribbean Sea...western Cuba...Yucatan Peninsula...and Gulf of Mexico region should monitor this situation carefully over the next few days. See special feature section below for additional details.

An upper vortex southeast of Bermuda is currently producing active weather as mentioned in paragraph P4. Although their is currently no computer model support for additional development...will be watching this system for potential subtropical cyclone development.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_12_2013_2345Z_zps823c93b2.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_12_2013_2345Z_zpsbfadb9f1.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN CARIBBEAN SURFACE TROUGH...
During the period between August 10 morning and August 11 early afternoon (between discussions #65 and #66)...weather over and east of the Lesser Antilles had been active due to a divergent upper westerly jet southeast of the upper vortex over the NE Caribbean Islands mentioned in paragraph P6 in the tropical belt section below. By discussion #66 (August 11 early afternoon) this thunderstorm activity had dwindled. In hindsight this maybe about the time a surface trough developed over the Lesser Antilles/eastern Caribbean region due to the divergent nature of the aforementioned westerly jet. As detailed in paragraph P6 below...the upper westerly jet has been replaced by eastern Caribbean upper anticyclone whose low shear and upper outflow has enhanced the surface trough with a co-located area of strong thunderstorms such that this system has been introduced into the National Hurricane Center tropical weather outlook within the last 24 hours. Interestingly this surface trough is being titled a tropical wave in the NHC tropical weather outlook while the NHC TAFB maps only show it as a surface trough...so for now I am considering this a regular surface trough instead of a tropical wave of African origin.

It appears this surface trough is the system that various computer model runs have been developing into a tropical cyclone over the northwestern Caribbean/southern Gulf of Mexico region by day 4. The CMC continues to suggests a stronger tropical cyclone with enough vertical coupling to feel influence of forecast eastern US upper trough (paragraph P1) such that it makes northward progress toward the south-facing US Gulf coast by day 6. The GFS continues to suggest a weaker cyclone...but has also switched to a northward track toward the south-facing US Gulf coast while suggesting this system evolving into a semi-tropical (rather than fully tropical) system supported by eastern divergence of eastern US upper trough.

...MID-LATITUDES DISCUSSION...
P1...988 mb surface frontal cyclone over SE Canada has moved northeastward into the Atlantic high seas between Canada and Greenland while deepening further to 985 mb in the last 36 hrs in the supportive eastern divergence region of associated upper vortex. The upper vortex has become recently stacked with the surface cyclone such that the surface cyclone should begin weakening directly below the non-divergent center of the upper vortex. The upper vortex leaves behind upper trough which has recently begun diving southward into the eastern US from Canada's Hudson Bay while its eastern divergence supports 1012 mb frontal depression over the Great Lakes region. Within the next few days...expect the upper trough will continue to amplify southward into the eastern US to the east of a western North America upper ridge forecast to develop. Western convergence of the upper trough supports surface ridge over the north-central US and central Canada. Low-level warm air south of the frontal cyclone supports southern US upper ridge which has spread eastward into the western Atlantic and northward into the north-central Atlantic due to westerly and southerly advection of the warm air ahead of the frontal cyclone.

P2...Upper trough over the north-central Atlantic has amplified into an Azores upper vortex located to the southeast of north-central Atlantic upper ridge mentioned in paragraph P1. 1016 mb frontal depression northwest of the Azores in the previous discussion has weakened to around 1020 mb while exiting the eastern divergent region of the upper vortex.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1025 mb center NE of the Azores supported by upper convergence on the back side of western Iberia upper trough mentioned in paragraph P4...as well as 1024 mb center southwest of the Azores supported by upper convergence on the back side of Azores upper vortex mentioned in paragraph P2. This surface ridge has a westward extension into the northern Gulf of Mexico supported by southeastern convergence of southern US/W Atlantic upper ridge mentioned in paragraph P1. In conjunction with south side of paragraph P6 eastern Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Cut-off upper trough has shifted eastward into the western Iberia peninsula of Europe in advance of paragraph P2 upper vortex coming in from the west. Cut-off upper vortex previously east of Bermuda has retrograded southward to the waters southeast of Bermuda around the southern US/W Atlantic upper ridge mentioned in paragraph P1. The west and south sides of this upper vortex is producing an organized curved band of thunderstorm activity supported by split flow upper divergence at the boundary between the upper vortex and aforementioned upper ridge. Eastern divergence of this upper vortex supports new surface trough. Paragraph P1 eastern US upper trough is expected to create weakness in the vicinity of Bermuda in the aforementioned upper ridge...and whatever surface features associated with upper vortex look to get trapped between paragraph P3 Atlantic surface ridge and paragraph P1 north-central US/central Canada surface ridge coming in from the west. Therefore in the next 72 hrs...this system looks to stall out after it retrogades to a location south of Bermuda. Due to the abundance of perhiperial upper divergence around the upper vortex and potential instability of the cold air of the upper vortex relative to warm 29 to 30 deg C waters...am watching this area for potential subtropical development even though their is no current computer model support.

P5...Upper layer of southwestern Gulf deep-layered vortex has retorgraded westward out of the scope of the above charts and well into Mexico while rounding the paragraph P1 southern US upper ridge. Surface layer of this vortex remains over the southwestern Gulf as a remnant surface trough supported by split flow upper divergence between easterlies south of the upper ridge and westerlies flowing into west side of paragraph P6 upper vortex.

P6...In the last 36 hrs...NE Caribbean upper vortex has rapidly retorgraded westward into the southern Gulf region. This has caused prior western Caribbean upper anticyclone to become de-amplified southward into an upper ridge over Central America...and has caused prior upper ridge over northern Colombia to amplify northward into the eastern Caribbean as an upper anticyclone in the wake of the upper vortex. All of this Caribbean upper ridging remains split from larger eastern Atlantic upper ridge by paragraph P4 upper vortex SE of Bermuda. The far eastern portion of this upper ridge has become inflated by latent heat relase of thunderstorms associated with paragraph P8 tropical wave...resulting in new inverted upper trough embedded in eastern Atlantic upper ridge (midway between the Lesser Antilles and Cape Verde Islands) in relatively lower upper-level pressures adjacent to the inflation.

P7...Tropical wave previously midway between the Lesser Antilles and Cape Verde Islands is currently approaching the Lesser Antilles and remains inactive while embedded in Saharan dry air mentioned in paragraph P3. Previous expectation was that this tropical wave would develop below favorable upper anticyclone currently developing between paragraph P4 upper vortex southeast of Bermuda and paragraph P6 upper vortex moving into the southern Gulf of Mexico. It appears the momentum for tropical development has now shifted to eastern Caribbean surface trough to the west of this tropical wave as detailed in above special feature section.

P8...Tropical wave previously passing over the Cape Verde Islands is now west of the islands currently featuring 1010 mb surface low pressure spin southwest of the islands and thunderstorm activity over the southeast half of this tropical wave. The northwest half is currently inactive while it appears poised to ingest unfavorable dry Saharan air mentioned in paragraph P3.

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2013 Atlantic Hurricane Season Birdseye Discussion #66

By: NCHurricane2009, 6:08 PM GMT on August 11, 2013

...SUNDAY AUGUST 11 2013 2:08 PM EDT...
Activity with western Gulf of Mexico surface trough has made landfall in eastern Mexico as mentioned in paragraph P5 below. Elsewhere...within the last couple of days computer model support for tropical cyclone formation in the northwest Caribbean and or Gulf of Mexico beginning 5 days from now has increased in association with the tropical wave that is currently midway between the Lesser Antilles and Cape Verde Islands. If current computer model support continues...I will be upgrading the tropical wave to a special feature in my next blog post. See paragraph P7 below for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_11_2013_1015Z_zps33ab8a29.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0728Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_11_2013_1515Z_zps39ce75ec.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...1001 mb frontal cyclone center over SE Canada has deepened further to 988 mb in the last 24 hrs while moving northeastward in the supportive eastern divergence region of associated upper vortex. The upper vortex leaves behind upper trough over Hudson Bay whose eastern divergence supports persistent 1006 mb surface center over eastern Hudson Bay. Within the next few days...expect the upper vortex to continue eastward into the Atlantic high seas while Hudson Bay upper trough will slowly amplify southward into the eastern US to the east of a western North America upper ridge forecast to develop. Western convergence of the upper trough supports surface ridge that has built across the central US from central Canada. Low-level warm air south of the frontal cyclone supports southern US upper ridge which is spreading eastward into the western Atlantic and northward into the south tip of Greenland due to westerly and southerly advection of the warm air ahead of the frontal cyclone.

P2...Upper trough persists over the north-central Atlantic. Eastern divergence of the upper trough supports supports relatively new frontal depression (not marked in the above atmo chart) east of Iceland that has absorbed the remnant of Dorian...as well as a northeast-moving 1016 mb frontal depression passing northwest of the Azores. Convergence behind the upper trough supports 1025 mb surface ridge presently that has moved northeastward to the waters SE of Greenland. The southwest extension of this surface ridge near Bermuda...supported by southeastern convergence of paragraph P1 southern US/W Atlantic upper ridge...has merged with west side of paragraph P3 open Atlantic surface ridge.

P3...Surface ridge dominating much of the open Atlantic is anchored by 1027 mb center NE of the Azores supported by upper convergence on the back side of upper trough east of the Azores mentioned in paragraph P4. In conjunction with south side of paragraph P6 eastern Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Cut-off upper trough previously over the Azores has shifted eastward into the waters east of the Azores in advance of paragraph P2 upper trough coming in from the west. New cut-off upper vortex...a southern fracture of the paragraph P2 upper trough...has developed east of Bermuda and is expected to retrograde southward and then westward around the southern US/W Atlantic upper ridge mentioned in paragraph P1.

P5...Western Gulf of Mexico surface trough mentioned in paragraph P5 of the previous discussion...central Gulf of Mexico upper vortex mentioned in paragraph P4 of the previous discussion...and tropical wave mentioned in paragraph P7 of the previous discussion...have merged into large deep-layered vortex with 1013 mb surface center in the southwestern Gulf of Mexico. With central US surface ridge and southern US upper ridge (both mentioned in paragraph P1) located due north...expect this system to continue westward in deep-layered easterly flow south of the ridging. Most of the weather with this system continues to be due west of the upper vortex where upper divergence is maximum where upper northerlies split with the upper easterlies on the south side of the ridging. However this weather has moved into eastern Mexico such that no additional tropical development is possible. Based on the behavior observed yesterday afternoon...expect the possibility of scattered western Gulf thunderstorms below the upper vortex associated with vertical instability generated by the air temp contrast between 31 deg C waters and colder upper air of upper vortex. Eastern divergnce of the upper vortex may allow for additional scattered thunderstorms in the central Gulf of Mexico.

P6..Southern Caribbean upper ridge and much larger upper ridge in the eastern Atlantic are split from each other by westward-retrogading upper vortex which is crossing the NE Caribbean islands. Due to the upper vortex coming in from the northeast...the southern Caribbean upper ridge has split into a western Caribbean upper anticyclone and another upper ridge over northern Colombia whose outflow has tremendously increased the thunderstorms over the ITCZ in the area.

P7...Tropical wave in the waters midway between the Lesser Antilles and Cape Verde Islands is currently inactive while embedded in Saharan dry air mentioned in paragraph P3. As the tropical wave nears the Lesser Antilles and eastern Caribbean in the next couple of days...expect it to remain inactive while suppressed by upper vortex currently east of Bermuda expected to dive south toward the area (paragraph P4). By days 4 and 5 as the tropical wave arrives into the western Caribbean region...the tropical wave is forecast to enter favorable upper winds below an upper anticyclone located between aforementioned upper vortex and a second upper vortex currently over the NE Caribbean Islands (paragraph P6) which will have retrograded into the Gulf of Mexico by that time. The CMC and GFS computer models suggest tropical cyclone formation from this system due to the favorable upper anticyclone. The CMC suggests a stronger tropical cyclone with enough vertical coupling to feel influence of forecast eastern US upper trough (paragraph P1) such that it makes northward progress toward the south-facing US Gulf coast by day 7. The GFS suggests a weaker/shallower tropical cyclone more influenced by surface ridge supported by western convergence of eastern US upper trough with a WNW track across the southwestern Gulf of Mexico and into eastern Mexico by day 7.

P8...Tropical wave previously emerging from Africa is currently passing over the Cape Verde Islands in the eastern tropical Atlantic. Latest water vapor imagery suggests the tropical wave continues to be embedded in a moist air layer with associated thunderstorms. However the lack of computer model support suggests the tropical wave appears positioned north enough with a large enough circulation such that it will ingest unfavorable dry Saharan air to the northwest mentioned in paragraph P3.

Updated: 6:35 PM GMT on August 11, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #65

By: NCHurricane2009, 2:59 PM GMT on August 10, 2013

...SATURDAY AUGUST 10 2013 11:00 AM EDT...
Eastern Caribbean surface low has dissipated within last 36 hours. Elsewhere...a surface trough in the western Gulf of Mexico has been introduced into the National Hurricane Center Tropical Weather Outlook but does not show signs of further organization as it moves into eastern Mexico. See paragraph P5 for details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_10_2013_1015Z_zps2b8731b1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z, and the 0723Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_10_2013_1015Z_zps8ccacf12.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...1003 mb surface frontal cyclone over eastern Hudson Bay has weakened to 1006 mb in the last 24 hrs while caught in non-divergent environment below upper vortex center...with eastern divergence of the upper vortex supporting relatively new and deepening 1001 mb center over SE Canada that will assume the dominance of this system. Western convergence of the upper vortex supports surface ridge building into the central US from central Canada. Low-level warm air south of the frontal cyclone supports southern US upper ridge which is spreading eastward into the western Atlantic due to westerly advection of the warm air ahead of the frontal cyclone.

P2...Upper trough persists over the north-central Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian currenty located just southwest of Iceland...as well as a northeast-moving 1018 mb depression passing west of the Azores along the lengthy front extending from ex-Dorian. Convergence behind the upper trough supports 1027 mb surface ridge presently just offshore of Newfoundland. This surface ridge has a southwest extension near Bermuda and over the SE US supported by southeastern convergence of paragraph P1 southern US/W Atlantic upper ridge.

P3...Surface ridge formerly dominating much of the open Atlantic is now confined to the eastern Atlantic in advance of the front mentioned in paragraph P2. The center anchoring this ridge...currently at 1030 mb...is supported by upper convergence between southerlies ahead of paragraph P4 upper trough over the Azores and mainstream mid-latitude westerlies. In conjunction with south side of paragraph P6 eastern Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Broad upper vortex previously over the central Bahamas has accelerated westward into the central Gulf of Mexico as expected while pushed by south side of southern US/W Atlantic upper ridge mentioned in paragraph P1. Southwestern of the two upper troughs southwest of the Azores has become absorbed by paragraph P2 upper trough coming in from the west while the northeastern of the two has arrived over the Azores.

P5...Surface troughing has moved from the central to western Gulf of Mexico while becoming focused below a maximum of split flow upper divergence between northwest side of paragraph P4 Gulf upper vortex and south side of P1 southern US upper ridge. Its increase in thunderstorms in the last 36 hrs has warrented its mention in the National Hurricane Center tropical weather outlook...but the fact that it is under northeastery vertical shear...that it is expected to make landfall in eastern Mexico in the next 24 hrs...and that the thunderstorms have not become more organized indicate that further development is unlikely.

P6..Southern Caribbean upper ridge and much larger upper ridge in the eastern Atlantic are split from each other by westward-retrogading upper vorticity east of the Lesser Antilles. Now that the paragraph P4 upper vortex has moved away into the central Gulf of Mexico...the southern Caribbean upper ridge has been able to expand northward in its wake in the last 36 hrs...and it expect it to evolve into western Caribbean upper anticyclone (as mentioned at the end of paragraph P7 of discussion #64) located in the gap between the central Gulf upper vortex and aforementioned upper vortex east of the Lesser Antilles.

P7...Tropical wave previously in the central Caribbean has arrived into the southeastern Gulf of Mexico and Yucatan peninsula. Its north end appears to be interacting with eastern divergence of paragraph P4 central Gulf upper vortex to produce thunderstorms over the southeastern Gulf of Mexico. Eastern Caribbean surface low presumably left behind by this tropical wave has dissipated within the last 36 hrs as it did not surivive long enough to take advantage of relaxation in westery vertical shear from northward growth of southern Caribbean upper ridge mentioned in paragraph P6.

P8...Tropical wave west of the Cape Verde Islands is moving into the waters midway between the Lesser Antilles while continuing to be suppressed by paragraph P3 Saharan dry air.

P9...Satellite imagery indicates that a possible tropical wave with large circulation is emerging from western Africa as marked in the lower-right corner of the above atmo chart. Just like the tropical wave in paragraph P8...this tropical wave appears north enough and appears to have a large enough circulation such that it will ingest unfavorable dry Saharan air to the northwest mentioned in paragraph P3.

Updated: 5:09 PM GMT on August 11, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #64

By: NCHurricane2009, 10:06 AM GMT on August 09, 2013

...FRIDAY AUGUST 9 2013 6:00 AM EDT...
Eastern Caribbean surface low has signifcantly weakened under a pulse of westerly vertical shear. Its greatest potential for a comeback is when it arrives in the western Caribbean in 48 hours. Because it is not clear if the surface low will survive the current unfavorable conditions...I have dropped it as a special feature on this blog. See paragraph P7 for details.

Eastern Atlantic tropical wave currently west of the Cape Verde Islands...mentioned in paragraph P8...has not become better organized while ingesting dry Saharan air. Therefore its potential for further development is very low at this time.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_8_2013_2345Z_zpsfc68f0ed.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0126Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_8_2013_2345Z_zpsd220eb25.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...1008 mb frontal cyclone previously arriving from central Canada has deepened to 1003 mb over eastern Hudson Bay due to supportive eastern divergence of its shortwave upper trough. Cool air advection on the back side of the cyclone has amplified the upper trough into an upper vortex to the southwest...while warm air advection ahead of the cyclone supports an upper anticyclone centered over the NE Canada coast. Low-level warm air south of the frontal cyclone supports southern US upper ridge mentioned in paragraph P1 of the previous discussion.

P2...Upper trough previously over eastern Canada and northwest Atlantic is transitioning into the north-central Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian currenty located east of Greenland...as well as a northeast-moving 1018 mb depression midway between Bermuda and the Azores along the lengthy front extending from ex-Dorian (this 1018 mb depression was the 1017 mb depression mentioned in paragraph P6 of the previous discsussion). Convergence behind the upper trough supports 1026 mb surface ridge presently just offshore of Newfoundland.

P3...Surface ridge dominates much of the open Atlantic basin. The dominant open Atlantic center anchoring this ridge...currently at 1030 mb...is supported by northeastern convergence of paragraph P6 eastern Atlantic upper ridge. In conjunction with south side of this upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Broad upper vortex previously over the eastern Bahamas has retrograded slowly westward into the central Bahamas. As the southern US upper ridge mentioned in paragraph P1 shifts northeastward into the NW Atlantic...the westward speed of this upper vortex will increase in the next 24 hrs while pushed by south side of the upper ridge. Elsewhere...pair of upper troughs previously ENE of Bermuda are now a pair of upper vortices southwest of the Azores that continue to shift northeast in advance of paragraph P2 upper trough coming in from the west.

P5...Surface troughing has moved from the eastern to central Gulf of Mexico while becoming focused bellow a maximum of split flow upper divergence between northwest side of paragraph P4 upper vortex and southeast side of P1 southern US upper ridge.

P6..The paragraph P4 broad upper vortex continues to split upper ridging into one upper ridge over the southern Caribbean whose outflow continues supporting an increase in thunderstorms over and south of Panama...and a second much larger upper ridge in the eastern Atlantic featuring retrograding and embedded upper vorticity stretching from the Canary Islands in the NE Atlantic to the waters east of the Lesser Antilles.

P7...Tropical wave continues across the central Caribbean. Its south end may be contributing to enhancement of Panama-area thunderstorms mentioned in paragraph P6 while its north end appears to be interacting with eastern divergence of paragraph P4 upper vortex to produce thunderstorms over easstern Cuba and eastern Bahamas. Eastern Caribbean surface low presumably left behind by this tropical wave a few days ago was upgraded to a special feature during the previous discussion. I was expecting it to have a favorable upper anticyclone located between paragraph P4 upper vortex to the northwest and paragrah P6 upper vorticity to the east...but the distance between the two upper vorticity features has narrowed such that the neareast upper anticyclone north of the Lesser Antilles has been wedged northward and away to the waters south of Bermuda. This has left the eastern Caribbean surface low in a jet of westerly shear on the north side of paragraph P6 southern Caribbean upper ridge and south side of paragraph P4 upper vortex. The surface low has weakened to an inactive surface trough. As paragraph P4 mentions...the west pace of the western upper vortex will increase...with the GFS computer model run by 48 hrs suggesting a western Caribbean upper anticyclone developing in the widening gap between it and paragraph P6 upper vorticity to the east. Therefore this surface trough...if it exists by 48 hrs...could make a comeback below such an anticyclone.

P8...To the southeast of embedded upper vorticity mentioned in paragraph P6...relatively higher pressures are supporting a low-latitude upper ridge axis whose enhanced poleward outflow was previously supporting enhanced thunderstorm activity of an eastern Atlantic tropical wave which is now west of the Cape Verde Islands. Despite the continued favorable upper winds...the tropical wave has ingested paragraph P3 Saharan dry air from the northwest such that no further development is expected at this time.

Updated: 10:08 AM GMT on August 09, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #63

By: NCHurricane2009, 12:58 AM GMT on August 08, 2013

...WEDNESDAY AUGUST 7 2013 9:00 PM EDT...
Broad surface tropical low crossing the Lesser Antilles into the eastern Caribbean has become better organized. Although it is currently rated at a low 10% chance of tropical cyclone formation on the NHC tropical weather outlook...I have upgraded it to a special feature on this blog due to its current organization and potential interaction with favorable upper winds as it crosses the Caribbean over the next few days. See special feature section below for additional details.

Eastern Atlantic tropical wave currently over the Cape Verde Islands also has the potential to stay with favorable upper winds as it journeys across the tropical Atlantic over the next few days. If it shows signs of becoming better organized I will also upgrade it to a special feature on this blog. See paragraph P9 for additional details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_7_2013_2045Z_zps4ac2f8a8.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 2223Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_7_2013_2045Z_zpsa1093b32.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN CARIBBEAN SURFACE TROPICAL LOW...
1012 mb surface tropical low was crossing the Lesser Antilles early this morning and as of this evening it is in the eastern Caribbean Sea. Visible satellite imagery before sunset suggested a well-defined low-level cloud swirl with a thunderstorm burst just to the south...as well as some banding features well to the southeast of the swirl extending across the southern Lesser Antilles and waters east of the southern Lesser Antilles.

West end of paragraph P7 east Atlantic upper ridge extends to upper anticyclone currently just north of the Lesser Antilles. As the paragraph P5 upper vortex and pargaraph P7 upper vorticity retrograde west...the favorable upper anticyclone located in between will also retrograde west. Despite the broad surface low and favorable upper anticyclone being currently phased with risk of the two staying phased in the next several hours (as they both track west across the Caribbean)...none of the reliable computer models currently develop this system.

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and attendant surface 1008 mb frontal cyclone is entering the upper-left of the above charts from central Canada.

P2...Upper trough persists over eastern Canada and northwest Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian (which has deepened further to 989 mb) that has recently passed by the south tip of Greenland and is currently in the waters east of Greenland. A local maximum of cool air advection behind ex-Dorian supports upper vortex south of Greenland. Low-level warm air southwest of the upper trough also supports southern US upper ridge. Convergence behind the upper trough supports 1024 mb surface ridge presently just offshore of the northeastern US.

P3...Amplified NE Atlantic upper trough and attendant surface cold front has moved into western Europe.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1016 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge...currently at 1027 mb...is supported by northeastern convergence of paragraph P7 eastern Atlantic upper ridge. In conjunction with south side of this upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex previously in the vicinity of Hispaniola (Haiti and the Dominican Repbulic) has retrograded slowly westward into the eastern Bahamas. Pair of upper troughs ENE of Bermuda are beginning to shift northeast in advance of paragraph P2 upper trough coming in from the west.

P6...Surface troughing in the eastern Gulf of Mexico persists in split flow upper divergence between west side of paragraph P5 upper vortex and paragraph P2 southern US upper ridge. This surface troughing extends eastward to 1017 mb depression in the vicinity of Bermuda...with this portion of surface troughing currently supported by split flow upper divergence between westerlies ahead of paragraph P2 upper trough and northeasterlies flowing into paragraph P5 upper vortex. The 1017 mb depression is located along the front extending from the remnant of Dorian.

P7..The paragraph P5 broad upper vortex continues to split upper ridging into one upper ridge over the southern Caribbean whose outflow continues supporting an increase in thunderstorms south of Panama...and a second much larger upper ridge in the eastern Atlantic featuring embedded upper vorticity due west and north of the Cape Verde Islands.

P8...Tropical wave previously crossing the eastern Caribbean is currently entering the central Caribbean. Expect the tropical wave to remain inactive while it is phased to slide below retrograding and suppressing upper vortex mentioned in paragraph P5. Cloudiness and thunderstorms to the southeast of the wave axis continue to show cyclonic turning and continue to be analyzed as a surface 1012 mb low pressure spin presumably left behind by this tropical wave. See above special feature section for additional details on 1012 mb low.

P9...To the southeast of embedded upper vorticity north and west of the Cape verde Islands mentioned in paragraph P7...relatively higher pressures are supporting a low-latitude upper ridge axis whose enhanced poleward outflow is supporting high thunderstorm activity at the south end of a tropical wave that has recently rolled off of Africa. This tropical wave was positioned over the Cape Verde Islands as of 1800Z NHC TAFB surface mapping. Computer model runs suggest the favorable low-latitude upper ridging will be retrograding westward in the wake of paragraph P7 upper vorticity also expected to retrograde westward. Therefore as this tropical wave continues west...their is a decent probability that it will remain phased with favorable upper winds over the next few days...and therefore I will be upgrading this tropical wave to a special feature if the thunderstorms become better organized.

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2013 Atlantic Hurricane Season Birdseye Discussion #62

By: NCHurricane2009, 8:59 AM GMT on August 07, 2013

...WEDNESDAY AUGUST 7 2013 4:50 AM EDT...
Tropical wave crossing the Lesser Antilles appears to have produced a broad tropical low pressure currently located in its wake. This broad surface low may encounter some favorable upper winds as it moves into the Caribbean later this week...although currently none of the reliable computer models develop this system. See paragraph P8 for details. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_6_2013_1945Z_zpsf77ac210.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_6_2013_1945Z_zps67a9fd35.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and attendant surface 1008 mb frontal cyclone is entering the upper-left of the above charts from central Canada.

P2...Upper trough persists over eastern Canada and northwest Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian (which has deepened to 997 mb) that has recently clipped by Newfoundland and is currently south of Greenland...as well as adjacent 1009 mb surface low over the SE Canada coast. Ex-Dorian and the 1009 mb surface low have absorbed 1008 mb surface low between Canada and Greenland mentioned in the previous discussion. A local maximum of cool air advection behind Ex-Dorian has resulted in formation of an upper vortex also located south of Greenland while warm air advection ahaed of Ex-Dorian supports persistent upper ridge over Greenland. Low-level warm air southwest of the upper trough also supports southern US upper ridge. Convergence behind the upper trough supports 1022 mb surface ridge moving offshore from the eastern US.

P3...Amplified NE Atlantic upper trough is working its way slowly into western Europe. 1009 mb surface frontal low SE of Newfoundland...mentioned in paragraph P2 of the previous discussion...is moving eastward into western Europe and has deepened to less than 1008 mb while taking advantage of eastern divergence of the upper trough.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1018 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge...currently at 1030 mb...is supported by western convergence of paragraph P3 NE Atlantic upper trough. In conjunction with south side of paragraph P7 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex persists in the vicinity of Hispaniola (Haiti and the Dominican Repbulic). Upper trough ENE of Bermuda has split into two upper troughs in advance of paragraph P2 upper trough coming in from the west.

P6...Surface troughing that was north of the Bahamas in the previous discussion...initiated by split flow upper divergence between the northerlies on the east flank of paragraph P2 southern US upper ridge and westerlies ahead of paragraph P2 upper trough...currently extends into the eastern Gulf of Mexico due to split flow upper divergence between west side of paragraph P5 upper vortex and paragraph P2 southern US upper ridge. The remainder of this surface troughing has consolidated into a 1015 mb depression in the vicinity of Bermuda located along the front extending from the remnant of Dorian.

P7..The paragraph P5 broad upper vortex continues to split low-latitude upper ridging into one upper ridge over the southern Caribbean whose outflow continues supporting an increase in thunderstorms south of Panama...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands and embedded upper vorticity due north of the Cape Verde Islands associated with southern cut-off of NE Atlantic upper trough as mentioned in paragraph P3 of the previous discussion.

P8...Tropical wave previously apporaching the Lesser Antilles is crossing the islands into the eastern Caribbean...and expect the tropical wave to remain inactive while it is phased to slide below retrograding and suppressing upper vortex mentioned in paragraph P5. Meanwhile...in the last 48 hrs satellite animation suggested cloudiness and thunderstorms to the southeast of the tropical wave axis with some cyclonic turning...and in the last 24 hrs this area has been upgraded to a broad surface 1012 mb low presumably left behind by the tropical wave. This broad surface low will soon be crossing the Lesser Antilles and into the Caribbean Sea behind its parent tropical wave. At the same time...west end of paragraph P7 east Atlantic upper ridge extends to upper anticyclone currently just north of the Lesser Antilles...and as the paragraph P5 upper vortex and pargaraph P7 upper vorticity retrograde west...the favorable upper anticyclone located in between will also retrograde west. Despite the broad surface low and favorable upper anticyclone becoming potentially phased while moving across the Caribbean...none of the reliable computer models currently develop this system.

P9...To the southeast of embedded upper vorticity north and west of the Cape verde Islands mentioned in paragraph P7...relatively higher pressures are supporting a low-latitude upper ridge axis over the Cape verde Islands whose enhanced poleward upper outflow has supported an increase in ITCZ thunderstorms offshore of Africa and south of the islands. Due to the high activity of the ITCZ in this area...it is difficult to distinguish by satellite alone any distinct thunderstorm clusters associated with any individual tropical waves that might be rolling off of Africa...and therefore I am depending on the NHC TAFB surface maps to tell me when and where the next African tropical wave may be located. So far NHC TAFB has not added any new tropical waves rolling off of Africa.

Updated: 9:04 AM GMT on August 07, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #61

By: NCHurricane2009, 2:14 AM GMT on August 06, 2013

...MONDAY AUGUST 5 2013 10:15 PM EDT...
Atlantic tropics loses its fizz in the wake of Dorian...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_5_2013_2045Z_zps784dcc61.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_5_2013_2045Z_zps421dff02.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough and attendant surface 1004 mb frontal depression is entering the upper-left of the above charts from central Canada.

P2...Upper trough persists over eastern Canada and northwest Atlantic. Eastern divergence of the upper trough supports the remnant low of Dorian currently passing by Newfoundland...adjacent new 1005 mb surface low over SE Canada...and surface low that has weakened from 1002 to 1008 mb in last 24 hrs while emerging from SE Canada and into the waters between Canada and Greenland. 1005 mb surface low NE of Newfoundland in previous discussion has weakened to 1009 mb while currently positioned SE of Greenland while exiting supportive eastern divergence region of the upper trough. Low-level warm air southwest of the upper trough supports southern US upper ridge...and low-level warm air advection ahead of the 1008 mb surface low between Greenland and Canada supports another upper ridge over Greenland. Convergence behind the upper trough supports 1020 mb surface ridge building into the eastern US.

P3...Amplified NE Atlantic upper trough is working its way slowly into western Europe. South fragment of upper trough has fractured at a location north of the Cape Verde Islands...and expect upper vorticity associated with this fracture to retrograde around the paragraph P7 eastern Atlantic upper ridge.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1020 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge...currently at 1030 mb...is supported by western convergence of paragraph P3 NE Atlantic upper trough. In conjunction with south side of paragraph P7 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex has retrograded southwestward into Hispaniola (Haiti and the Dominican Repbulic) while moving around paragraph P1 southern US upper ridge. Relatively new upper vortex ENE of Bermuda has opened into an upper trough in advance of paragraph P2 upper trough coming in from the west.

P6...Surface trough was extending southward from the remnant low of Dorian during the previous discussion...and even though the remnant of Dorian has exited the tropical belt this surface trough perists at a location north of the Bahamas while supported by split flow upper divergence between the northerlies on the east flank of paragraph P2 southern US upper ridge and westerlies ahead of paragraph P2 upper trough.

P7..The paragraph P5 broad upper vortex continues to split low-latitude upper ridging into one upper ridge over the southern Caribbean whose outflow continues supporting an increase in thunderstorms in the area...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands. The southern Caribbean upper ridge has de-amplified in the last 24 hrs as the paragraph P5 upper vortex is squashing it while coming in from the northeast.

P8...Tropial wave previously midway between the Lesser Antilles and Cape Verde Islands is apporaching the Lesser Antilles and will be crossing the islands in the next 24 hrs. With the exception of cloudiness and thunderstorm clouds to the southeast of its axis...this tropical wave remains inactive while embedded in dry Saharan air mentioned in paragraph P4.

Updated: 2:15 AM GMT on August 06, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #60

By: NCHurricane2009, 4:31 PM GMT on August 04, 2013

...SUNDAY AUGUST 4 2013 12:31 PM EDT...
Tropical Depression Dorian degenerates into remnant low offshore of the southeastern United Staes as of yesterday afternoon and will be merging with a frontal boundary as it transitions into a non-tropical remnant gale. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_4_2013_1315Z_zps5217f71f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z, and the 1327Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_4_2013_1315Z_zpsa092708b.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough persists over eastern Canada and the northeastern US. Eastern divergence of the upper trough formerly supported frontal cyclone centered over NE Hudson Bay which has since lifted northward out of the above charts while weakening below the upper trough axis. Eastern divergence of the upper trough now supports 1002 mb frontal depression that has moved from the Great Lakes to SE Canada in the last 36 hrs as well as a 1005 mb frontal depression that has tracked from offshore of the NE US and into the waters NE of Newfoundland in the last 36 hrs. Low-level warm air southwest of the upper trough supports southern US upper ridge...and low-level warm air advection ahead of the 1002 and 1005 mb frontal depressions supports western Atlantic upper ridge which has recently split into an eastern extension of southern US upper ridge and another upper ridge over Greenland. Convergence behind the upper trough supports 1025 mb surface ridge building into the central US from central Canada.

P2...Deep-layered vortex south of Greenland and NE Atlatnic upper trough have merged into amplified upper trough and surface frontal system offshore of western Europe.

P3...Surface ridge dominates much of the open Atlantic basin...with a current westward 1019 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P1 southern US upper ridge. The dominant open Atlantic centers anchoring this ridge...currently at 1022 and 1030 mb...are supported by western convergence of paragraph P2 NE Atlantic upper trough and SE convergence of paragraph P1 western Atlantic upper ridge. In conjunction with south side of paragraph P6 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P4...Broad upper vortex previously NE of the Lesser Antilles is beginning to retrograde southwestward into the the NE Caribbean Sea while moving around paragraph P1 western Atlantic upper ridge. A new upper vortex ENE of Bermuda has developed in relatively lower pressures between paragraph P1 western Atlantic upper ridge and paragraph P6 eastern Atlantic upper ridge.

P5...Tropical wave previously moving into the Bay of Campeche and SE Mexico has exited the scope of this blog while moving into the eastern Pacific. What is left of inverted upper trough over the western Caribbean is a small upper vortex moving into the Yucatan while retrograding around paragraph P1 southern US upper ridge. Tropical Depression Dorian offshore of the SE US has collapsed into a remnant low as of yesterday afternoon due to northerly vertical wind shear on east flank of southern US upper ridge...but has recently deepened to 1010 mb and developed a southward extending surface trough with thunderstorms due to split flow upper divergence between the northerlies on the east flank of southern US upper ridge and westerlies ahead of paragraph P1 upper trough. In the next 24 hrs...expect the remnant of Dorian to accelerate NE across the open NW Atlantic while transitioning into a non-tropical frontal low supported by eastern divergence of paragraph P1 upper trough (and as such I will move it to the mid-latitudes section during my next discussion).

P6..The paragraph P4 broad upper vortex continues to split low-latitude upper ridging into one upper anticyclone (upper ridge) over the southern Caribbean whose outflow continues supporting an increase in thunderstorms in the area...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands.

P7...Tropial wave previously west of the Cape Verde Islands is now midway between the Lesser Antilles and Cape Verde Islands. With the exception of thunderstorms along the ITCZ at its south end...this tropical wave remains inactive while embedded in dry Saharan air mentioned in paragraph P3 and supressive (non-divergent) environment of inverted upper trough mentioned in paragraph P6.

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2013 Atlantic Hurricane Season Birdseye Discussion #59B (Special Update)

By: NCHurricane2009, 10:59 AM GMT on August 03, 2013

...SATURDAY AUGUST 3 2013 7:00 AM EDT...
This special update is released to issue a forecast on Tropical Depression Dorian which reformed offshore of the east Florida coast as of 5 AM EDT...

Looking at Figure 1 below and the NHC's 5 AM EDT coordinates...it is clear that the NHC positioned Dorian based on a recent ASCAT pass of low-level winds. What is very confounding at this hour is that simulatenous shortwave infrared satellite imagery low-level cloud motions in Figure 2 suggest the center of Dorian is zooming off to the north-northeast and already passing 30N latitude! Perhaps Dorian is accelerating to the north-northeast while finally finding a break in the subtropical ridge (between the 1019 mb and 1026 mb centers mentioned in paragraph P4 of discussion #59) induced by 1001 mb frontal cyclone mentioned in paragraph P1 of discussion #59. As shown in Figure 3...I will take a solution between the Figure 1 ASCAT and Figure 2 shortwave infrared center fixes and say Dorian will be moving NNE and be just north of 30N latitude by 11 AM EDT later this morning. If my 11 AM forecast position is to become true...this means Dorian will be in the midst of northerly shearing upper winds (on east flank of southern US upper ridge mentioned in paragraph P1 of discussion #59) shown by the 200 mb barbs in Figure 2 while leaving behind its thunderstorm cluster and small upper anticyclone. This is why I forecast Dorian to already be dissipating by 11 AM this morning. However if my assessment proves to be wrong when the 11 AM NHC advisory comes out and indeed Dorian remains centered much closer to the thunderstorms and upper anticyclone...I may have to issue another special update later today to put out a revised forecast.
 photo Aug_03_2013_ASCAT_pass_for_Dorian_zpseec5e9fb.png
Figure 1: ASCAT pass of Dorian's surface winds as of 5 AM EDT.

 photo Aug_03_2013_ShortwaveIR_for_Dorian_zps524d4af2.png
Figure 2: Shortwave Infrared satellite imagery taken around 5 AM EDT. Blue-colored clouds are colder high-level clouds while black-colored clouds are more low-level. Red arrows are drawn in to show the low-level cloud motion which suggests a center located further north-northeast of the Figure 1 ASCAT center fix. Also included are 200 mb (upper-level) light-blue wind barbs which show that if Dorian is indeed zooming off to the north-northeast that he is quickly entering a hostile northerly shear environment.

 photo Aug_3_2013_TD_Dorian_Forecast_zps2645dd77.png
Figure 3: My forecast versus the NHC's 5 AM EDT forecast on Tropical Depression Dorian

Impact swath in Figure 3 assumes Dorain's thunderstorm cluster and upper anticyclone will gradually diminish at its current location while becoming seperated from the supportive surface convergence of Dorian's surface center zooming off to the north-northeast (albeit the also-supportive upper outflow of the upper anticyclone may allow these thunderstorms to linger well after Dorian's surface center leaves the area). Size of impact swath is based on assessing current size of thunderstorm cluster using the thickest clouds displayed on colorized infrared satellite imagery and radar imagery from Florida.

Return to full discussion #59 for an assessment on the rest of the Atlantic tropics...

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2013 Atlantic Hurricane Season Birdseye Discussion #59A (Special Update)

By: NCHurricane2009, 9:12 AM GMT on August 03, 2013

...SATURDAY AUGUST 3 2013 5:11 AM EDT...
While I was composing full discussion #59 overnight...the remnant low of Dorian just offshore of Florida's east coast re-fired a circular thunderstorm burst just south of its surface center with sufficiently strong winds such that the remnant low has been promptly re-upgraded to a tropical depression as of 5 AM EDT. I will be releasing a forecast for Tropical Depression Dorian within the next couple of hours in another special update to follow. Ignore all remarks in full discussion #59 stating that the remnant of Dorian was not re-generating....

Return to full discussion #59 for an assessment on the rest of the Atlantic tropics...

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2013 Atlantic Hurricane Season Birdseye Discussion #59

By: NCHurricane2009, 9:05 AM GMT on August 03, 2013

...SATURDAY AUGUST 3 2013 4:30 AM EDT...
With the remnants of Dorian not re-generating into a tropical cyclone and vigorous eastern Atlantic tropical wave ingesting Saharan dry air...the Atlantic tropics remain calm.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_2_2013_2245Z_zps09404fd3.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1927Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_2_2013_2245Z_zps4344b770.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough persists over eastern Canada and the northeastern US. Eastern divergence of the upper trough supports surface 1001 mb frontal cyclone currently centered over eastern Hudson Bay...and eastern divergence of an embedded shortwave upper trough diving southeast support secondary 1009 mb frontal depression over the Great Lakes. Low-level warm air southwest of the 1001 and 1009 mb systems supports southern US upper ridge...and low-level warm air advection ahead of the 1001 mb frontal cyclone supports western Atlantic upper anticyclone. Divergence ahead of the upper trough also supports 1008 mb frontal depression offshore of the NE US along the lengthy front trailing from 1005 mb frontal cyclone mentioned in paragraph P2 below. Convergence behind the upper trough supports 1018 mb surface ridge over the SE US as well as a building surface ridge in the north-central US and central Canada.

P2...Upper trough previously along the east Canada coast has moved offshore as an upper vortex passing south of Greenland. Center of associated surface frontal cyclone...currently at 1005 mb...has whilred beneath the upper vortex...resulting in a deep-layered system south of Greenland.

P3...Upper trough in the NE Atlantic is gradually working its way into wesern Europe.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1019 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P1 southern US upper ridge. The dominant open Atlantic centers anchoring this ridge...currently at 1026 and 1028 mb...are supported by western convergence of paragraph P3 NE Atlantic upper trough and SE convergence of paragraph P1 western Atlantic upper anticyclone. In conjunction with south side of paragraph P7 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex NE of the Lesser Antilles has become compressed into a SW-NE strecth of upper vorticity extending into the eastern Caribbean while squashed between amplifying paragraph P1 W Atlantic upper anitcyclone and paragraph P7 eastern Atlantic upper ridge.

P6...Tropical wave previously moving into the Yucatan is now in the Bay of Campeche and SE Mexico and is largely inactive due to SE convergence of paragraph P1 southern US upper ridge. Upper vortex over Cuba has weakened into an inverted upper trough over the western Caribbean as continued latent heat release associated with ex-Dorian's thunderstorms offshore of Florida has built a small upper anticyclone just due north. The remnant of Dorian has matured further into a 1016 mb surface low along the east Florida coast. Looking ahead...the paragraph P4 1019 mb center in the Gulf of Mexico will become replaced by paragraph P1 surface ridge buidling into the central US from central Canada...allowing for this system to turn northward along the east Florida coast while steered by west side of paragraph P4 1026 mb center. However this north track will be slow due to blocking effect of paragraph P1 central US surface ridge. This northward track is beginning to take this system into unfavorable northerly shear and upper convergence on the SE quad of paragraph P1 southern US upper ridge that will likely suppress additional development. Early signs of northerly shear include the fact that the surface low pressure of Dorian is on the north side rather than totally under its thunderstorms.

P7..The paragraph P5 upper vorticity continues to split low-latitude upper ridging into one upper anticyclone (upper ridge) over the southern Caribbean whose outflow continues supporting an increase in thunderstorms in the area and the development of a 1010 mb surface low along the ITCZ...and a second upper upper ridge in the eastern Atlantic featuring an embedded inverted upper trough due west of the Cape Verde Islands.

P8...Due to the fact that NHC TAFB has not added a tropical wave I suspected between the Lesser Antilles and Cape Verde Islands...I have cancelled it as marked in the above atmospheric features chart.

P9...Tropial wave with 1009 mb surface low is now west of the Cape Verde Islands with its south half continuing to be active with thunderstorms. As previously expected...the surface low's cyclonic circulation has pulled in and ingested paragraph P4 dry Saharan air from the northwest such that further development from this tropical wave is not expected.

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2013 Atlantic Hurricane Season Birdseye Discussion #58

By: NCHurricane2009, 5:14 AM GMT on August 02, 2013

...FRIDAY AUGUST 2 2013 1:15 AM EDT...
Stubborn remnants of Dorian became better organized over the western Bahamas this past afternoon but are not as well organized this evening. Although the National Hurricane Center suggests a moderate chance of tropical cyclone reformation from this system...I have not upgraded it to a special feature on this blog for reasoning stated in paragraph P6. However if this system shows more imminent signs of regenerating into a tropical cyclone I may issue special updates between now and the next blog post.

A tropical wave that has emerged from Africa...mentioned in paragraph P9 below...shows signs of becoming better organized. However due to dry air that lies ahead I have not upgraded this to a special feature on this blog.

The GOES satellite calculated 200 mb wind barbs referred to in the atmospheric features chart caption were not available at the time I generated the chart. The upper air analysis in that chart was instead done using 300 mb wind barbs shown in the 12Z GFS model initialization available at http://moe.met.fsu.edu/tcgengifs/.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_1_2013_1845Z_zpsb36cfd9c.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1930Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_1_2013_1845Z_zps74e1a0fb.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Upper trough previously over central Canada and central US is transitioning into eastern Canada and the eastern US. Eastern divergence of the upper trough supports surface 999 mb frontal cyclone currently centered over Hudson Bay. Low-level warm air southwest of the frontal cyclone supports southern US upper ridge...and low-level warm air advection ahead of the frontal cyclone supports western Atlantic upper anticyclone. Divergence ahead of the upper trough also supports 1014 mb frontal depression offshore of the NE US along the lengthy front trailing from 1003 mb frontal cyclone mentioned in paragraph P2 below. Convergence behind the upper trough supports surface ridge building into the central US.

P2...Upper trough is currently along the east Canada coast. Center of associated surface frontal cyclone...currently at 1003 mb...has moved offshore into the waters between Canada and Greenland. Low-level southerly warm air advection ahead of the frontal cyclone supports amplified upper ridge that has moved from the NW Atlantic and into the north-central Atlantic.

P3...Upper trough persists in the NE Atlantic and has become amplified due to cool air advection behind deepening surface frontal cyclone moving into western Europe.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1017 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P1 southern US upper ridge. The dominant open Atlantic center anchoring this ridge is currently 1028 mb supported by western convergence of paragraph P3 upper trough. In conjunction with south side of paragraph P7 east Atlantic upper ridge...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex NE of the Lesser Antilles remains generally stationary while trapped between paragraph P1 W Atlantic upper anitcyclone and paragraph P7 eastern Atlantic upper ridge. Surface trough below this upper vortex has dissipated.

P6...Previously I thought the remnant of Dorian is the tropical wave currently moving into the Yucatan peninsula from the western Caribbean...however official opinion suggests the remnant of Dorian is the Bahamas surface trough interacting with upper vortex mentioned in paragraph P6 of the previous discussion. It appears latent heat release from the persistent t-storm activity of the surface trough has displaced the upper vortex center southward into Cuba...with split flow upper divergence between easterlies on north side of the upper vortex and southerlies on west side of paragraph P1 W Atlantic upper anticyclone allowing the surface trough and thunderstorms to intensify and become better organized over the western Bahamas this past afternoon. Looking ahead...the paragraph P4 1017 mb center in the Gulf of Mexico will become replaced by paragraph P1 central US surface ridge...allowing for this system to turn northwest across the Florida peninsula/eastern Gulf area while steered by west side of paragraph P4 1028 mb center. However this northwest track will be slow due to blocking effect of paragraph P1 central US surface ridge. This forecast track will place this system below the convergent SE quad of paragraph P1 southern US upper ridge that will suppress additional development (unless the thunderstorms release enough latent heat such that it builds an upper outflow structure within the SE quad of the upper ridge). This coupled with land interaction potential with the Florida peninsula makes me currently lean toward a solution where this system does not redevelop into a tropical cyclone (in fact the only model that currently redevelops Dorian is the overly-agressive CMC model). However should this system shows more imminent signs of regenerating into a tropical cyclone I may issue special updates between now and the next blog post.

P7..The paragraph P5 and P6 upper vortices continue to split low-latitude upper ridging into one upper anticyclone (upper ridge) over the southern Caribbean whose outflow continues supporting an increase in thunderstorms in the area...and a second upper upper ridge in the eastern Atlantic. Due to amplification of NE Atlantic upper trough (paragraph P3)...the east Atlantic upper ridge has split into an anticyclone as well as an upper ridge in the vicinity of the Cape Verde Islands and W Africa. Relatively lower pressures between the anticyclone and upper ridge supports the development of a new inverted upper trough due west of the Cape Verde Islands.

P8...While watching the westward propagation of enhanced thunderstorms along the ITCZ...I have moved the location of a suspect tropical wave (currently not marked in NHC TAFB surface maps) into the waters midway between the Cape Verde Islands and Lesser Antilles.

P9...Eastern cyclonic gyre previously marked as a 1008 mb surface low just east of the Cape verde Islands has been upgraded to a tropical wave with a 1009 mb surface low...and thunderstorms in its south half have become better organized since this evening began. In addition...computer model runs suggest this tropical wave will generally be in low shear and potentially enhanced upper outflow below the paragraph P7 eastern Atlantic upper ridge. However the northerly position of the 1009 mb surface low on the tropical wave suggests high potential for the surface low's cyclonic circulation to pull in and ingest paragraph P4 dry Saharan air from the northwest such that I currently assess tropical cyclone formation risk from this tropical wave is low.

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2013 Atlantic Hurricane Season Birdseye Discussion #57A (Special Update)

By: NCHurricane2009, 10:42 PM GMT on August 01, 2013

...THURSDAY AUGUST 1 2013 6:45 PM EDT...
In paragraph P6 of discussion #57 released early this morning...I identified the remnants of Dorian as the tropical wave progressing into the western Caribbean. It is now official opinion that the Bahamas surface trough supported by eastern divergence of overhead upper vortex...also mentioned in paragraph P6...is instead the remnant of Dorian. My next full discussion released later tonight will reflect this.

It is also worth noting that the remnant of Dorian has become better organized while moving into the western Bahamas. I will be assessing whether or not the remnant should be upgraded to a special feature on tonight's blog post depending on the probability of eventual tropical cyclone reformation from this system.

Updated: 10:45 PM GMT on August 01, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #57

By: NCHurricane2009, 8:08 AM GMT on August 01, 2013

...THURSDAY AUGUST 1 2013 4:10 AM EDT...
Atlantic tropics remain quiet as the month of August kicks off. June and July have totaled four tropical cyclones in the Atlantic...which is an above average pace when compared to the 1966 to 2009 climatological data available on the National Hurricane Center site (http://www.nhc.noaa.gov/climo/images/cum-average_ Atl_1966-2009.gif).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_31_2013_2045Z_zps5f43c114.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 2217Z-released WPC analysis.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_31_2013_2045Z_zpseacee52e.png
This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...MID-LATITUDES DISCUSSION...
P1...Shortwave upper trough previously emerging from the NW US and western Canada is currently over central Canada and the central US. Eastern divergence of the upper shortwave supports surface 1000 mb frontal cyclone currently centered on the coast of Hudson Bay at the Manitoba/Ontario border. Divergence ahead of the shortwave also supports 1013 mb frontal depression moving into the Ohio Valley along the lengthy front trailing from 1004 mb frontal cyclone mentioned in paragraph P2 below. Convergence behind the shortwave supports 1022 mb surface ridge centered over SE Montana.

P2...Upper trough persists over far eastern Canada and the NW Atlantic. Center of associated surface frontal cyclone...currently at 1004 mb...has moved from the Gulf of St Lawrence northward into the east coast of Canada while deepening in the supportive eastern divergence of the upper trough. Western convergence of the upper trough supports 1021 mb surface ridge centered just offshore of the NE US. Low-level warm air southwest of the frontal cyclone supports southern US upper ridge...and low-level southerly warm air advection ahead of the frontal cyclone supports amplified NW Atlantic upper anticyclone.

P3...Upper trough continues moving across the NE Atlantic...with its eastern divergence supporting a deepening 1004 mb surface frontal low moving into western Europe...and with its western convergence supporting a 1028 mb surface ridge that is becoming the dominant center of P4 surface ridge.

P4...Surface ridge dominates much of the open Atlantic basin...with a current westward 1020 mb extension into the Gulf of Mexico. The westward extension is supported by SE convergence of paragraph P2 southern US upper ridge. The dominant open Atlantic center anchoring this ridge is transitioning to the 1028 mb center mentioned in paragraph P3 above. In conjunction with south side of paragraph P2 NW Atlantic upper anticyclone...the south side of this surface ridge is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

...TROPICAL BELT DISCUSSION...
P5...Broad upper vortex NE of the Lesser Antilles is becoming stationary while further westward progression is blocked by southern US upper ridge mentioned in paragraph P2. Surface trough below continues west and has arrived to the waters east of Bermuda under the west side of the upper vortex.

P6...Upper vortex remains parked over the Bahamas...and according to the NHC tropical weather discussion from 8 PM EDT last night the increase in thunderstorms and development of new surface trough over the Bahamas is associated with eastern divergence of the upper vortex. Meanwhile the remnant tropical wave of Dorian previously under this upper vortex has continued westward into the western Caribbean region...and this remnant wave remains inactive while suppressed by paragraph P4 dry Saharan air as seen by brown shading in above thermo chart.

P7..The paragraph P5 and P6 upper vortices continue to split low-latitude upper ridging into one upper anticyclone (upper ridge) over the southern Caribbean whose outflow has contributed to an increase in thunderstorms (and perhaps surface convergence from the tropical wave in paragraph P6 may have also kick started these storms)...and a second upper anticyclone (upper ridge) in the eastern Atlantic.

P8...Tropical wave previously midway between the Cape Verde Islands and Lesser Antilles appears to have dissipated within the paragraph P4 dry Saharan air mass and was removed from NHC TAFB surface maps as of 1800Z last night.

P9...Western cyclonic gyre previously marked as a 1012 mb surface low just west of the Cape Verde Islands is no longer marked on NHC TAFB maps but continues to display cyclonic rotation within the paragraph P4 dry Saharan air mass as well as a southern thunderstorm cluster. As a result of the persistent cyclonic rotation I have upgraded this to a suspect tropical wave moving into the waters midway between the Lesser Antilles and Cape Verde Islands. The eastern cyclonic gyre previously marked as a 1008 mb surface low over western Mauritania is now marked as a 1010 mb surface low within a northward kink of the ITCZ just east of the Cape Verde Islands as of 1800Z last night.

Updated: 8:10 AM GMT on August 01, 2013

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