2013 Atlantic Hurricane Season Birdseye Discussion #54

By: NCHurricane2009 , 12:20 AM GMT on July 29, 2013

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...SUNDAY JULY 28 2013 8:22 PM EDT...
Remnant tropical wave of Dorian has not regenerated into a tropical storm and will be entering less favorable upper winds below an upper vortex settling over the Bahamas. Therefore I have cancelled it as a special feature on this blog.

Elsewhere...activity along a decaying frontal boundary offshore of the United States east coast has diminished. Eastern Atlantic tropical wave is no longer a special feature on this blog while ingesting dry Saharan air.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_28_2013_1815Z_zpsd379c6e1.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z, and the 1922Z-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_28_2013_1815Z_zps543918c3.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 vortex previously over Lake Michigan is now centered over the Michigan lower peninsula. Center of 1010 mb surface frontal cyclone has moved from Lake Superior and into southeastern Ontario while deepening to 1008 mb while supported by upper divergence between easterlies on the north side of the upper vortex and mainstream mid-latitude westerlies. Western convergence of upper vortex supports 1017 mb surface ridge over south-central Canada and central US.

P2...Upper trough previously over the Nw Atlantic...NE US...and far eastern Canada is now entirely in the NW Atlantic...with its eastern divergence supporting a 1008 mb surface frontal low that has tracked from Nova Scotia and into the waters just east of Newfoundland in the last 24 hrs...and with its western convergence supporting a 1023 mb surface ridge along the east coast of Canada. Northern fragment of this upper trough and associated less-than-1000 mb frontal cyclone previously moving across southern Greenland have mostly overtaken the NE Atlantic upper trough and surface low mentioned in paragraph P3 below. The front extending from the aforementioned 1008 mb low just east of Newfoundland was producing activity offshore of the eastern US that was monitored for tropical development during the previous discussion...but this is no longer the case as the cold front from the SE Ontario cyclone (paragraph P1) is overtaking this area (the only artifact left from this activity is the remnant 1013 mb low of disturbance Invest 90-L currently over eastern Massachusetts). Lastly...low-level warmer air ahead and south of the aforementioned SE Ontario frontal low...1008 mb frontal low east of Newfoundland...and less-than-1000 mb frontal low moving into the NE Atlantic...supports upper ridging over the SW US...northern Gulf of Mexico...and strong upper anticyclone over the north Atlantic which has recently split into two upper anticyclones due to the digging in of the NW Atlantic upper trough mentioned at the beginning of this paragraph.

P3...Large NE Atlantic upper trough is ever so slightly moving toward Europe while trying to defeat deep-layered ridge over Europe. The surface low pressure center formerly supported by eastern divergence of this upper trough has finally moved NE into the British Isles...but has become absorbed by the front of the less-than-1000 mb cyclone mentioned in paragraph P2. What is left of the absorbed surface low pressure system is a western Europe front marked in the upper-right corner of the above atmo chart and a surface trough SW of the Canary Islands and NW of the Cape Verde Islands that is beginning to retrograde westward around the south side of the paragraph P4 surface ridge.

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 SW US upper ridge. The remainder of the surface ridge has weakened to 1026 mb and shifted west while transitioning to being supported by SE convergence of the western of the two north Atlantic upper anticyclcones mentioned at the end of paragraph P2.

P5...Upper vortex south of Bermuda is retrograding westward into the Bahamas while steered by western of the two north Atlantic upper anticyclones mentioned at the end of paragraph P2. In the next 24 hrs...the upper vortex will begin stalling over the Bahamas as further westward progression blocked by SW US and northern Gulf of Mexico upper ridge mentioned in paragraph P2.

...TROPICAL BELT DISCUSSION...
P6...Broad and retrograding upper vortex west of the Cape Verde Islands...along with the paragraph P5 upper vortex south of Bermuda...has split low-latitude upper ridging into one upper anticyclone over Central America...a second upper anticyclone in the vicinity of the Lesser Antilles and over the remnants of Dorian...and a third upper ridge north of the Cape Verde Islands and into western Africa. South end of aforementioned upper anticyclone in the vicinity of the Lesser Antilles...in conjunction with the south end of the paragraph P4 surface ridge and south end of paragraph P2 north Atlantic upper anticyclones...is advecting dry Saharan air from Africa as seen by low-latitude brown shading in the above thermo chart.

P7...Area of south-central Caribbean thunderstorms mentioned in paragraph P7 of the previous discussion has transitioned into Central America while associated with the outflow of Central America upper anticyclone.

P8...Remnant tropical wave of Dorian earlier today showed signs of attempting to regenerate into a tropical storm due north of the Lesser Antilles while taking advantage of outflow of Lesser Antilles area upper anticyclone mentioned in paragrpah P6. While reconnaissance aircraft indicated that this system continues to produce tropical storm force winds of about 40 mph...a closed surface circulation could not be spotted and therefore technically Dorian could not be re-classified as a tropical storm. As the remnant tropical wave moves toward the Bahamas during the next day or so...expect its activity and intensity to reduce while becoming suppressed by paragraph P5 upper vortex also settling into the Bahamas.

P9...Tropical wave axis previously over and south of the Cape Verde Islands is now west and southwest of the islands. The previous and organizing thunderstorm cluster east of the wave axis enhanced by outflow of paragraph P6 upper ridge in the vicinity of the Cape Verde Islands extending into W Africa seemed to have potential to develop while the upper ridge was expected to expand in the wake of the broad and retrograding upper vortex mentioned at the beginning of paragraph P6. Now that this thunderstorm cluster has diminished...this tropical wave is no longer interesting and therefore is no longer a special feature on this blog. Tropical wave axis will proceed westward while phased with suppressing retrograding upper vortex and Saharan dry air mentioned in paragraph P6.

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5. WunderAlertBot (Admin)
1:04 AM GMT on July 30, 2013
NCHurricane2009 has created a new entry.
4. nigel20
5:20 AM GMT on July 29, 2013
Quoting nigel20:

The dry is is always there. It also a lot less than it was at the same time last year and even 2010. It is very likely that the latter half of August into September will be very active.

We should also remember that the peak of the hurricane season is sometime away and conditions will likely improve by then. The Southern Oscillation Index (SOI) is currently in positive Territory which is hinting at ENSO-neutral conditions throughout most if not all of the hurricane season. I'm sure that NCH will elaborate further.
Member Since: November 6, 2010 Posts: 11 Comments: 7828
3. nigel20
5:15 AM GMT on July 29, 2013
Quoting hatrickp:
Amazing how quickly that new tropical wave died under the Saharan dry air. Dry air seems to have dominated the Atlantic tropics for most of July, is that unusual? I don't remember nearly as much of it around last year. Why has it been so prominent this time, and what would it take to moisten up the air a bit?

The dry is is always there. It also a lot less than it was at the same time last year and even 2010. It is very likely that the latter half of August into September will be very active.
Member Since: November 6, 2010 Posts: 11 Comments: 7828
2. hatrickp
2:08 AM GMT on July 29, 2013
Amazing how quickly that new tropical wave died under the Saharan dry air. Dry air seems to have dominated the Atlantic tropics for most of July, is that unusual? I don't remember nearly as much of it around last year. Why has it been so prominent this time, and what would it take to moisten up the air a bit?
Member Since: August 20, 2012 Posts: 0 Comments: 14
1. nigel20
12:56 AM GMT on July 29, 2013
Thanks NCH! It has been a very interesting hurricane season do far and it should get even more interesting in a couple weeks or so.
Member Since: November 6, 2010 Posts: 11 Comments: 7828

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