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2013 Atlantic Hurricane Season Birdseye Discussion #1D (Special Update)

By: NCHurricane2009, 1:07 AM GMT on May 31, 2013

...THURSDAY MAY 30 2013...9:07 PM EDT...
The following is an update to the two areas of interest in the Atlantic basin highlighted in special update #1B early this morning...

Area # 1....Update on Eastern Pacific Tropical Depression Barbara....

While continuing to be pulled northward between the flow of the low-level Atlantic subtropical ridge and central US frontal system...Barbara has continued across southeastern Mexico and has emerged onto the Bay of Campeche coast. However with visible satellite imagery and surface observations not agreeing upon where Barbara is centered...the NHC has declared Barbara a remnant low with a poorly-defined center...and as such I will not be issuing a full birdseye discussion (with embedded Barbara forecast) tonight. With t-storm bands becoming biased east of the remnant low of Barbara...visible satellite before sunset suggests Barbara has finally traveled north enough such that its getting ripped apart by westerly vertical shear north of the tropical upper ridging.

With model runs showing tropical upper ridging persisting over Central America...SE Mexico...and over the Bay of Campeche...watching for sustenance of a quasi-stationary broad surface tropical low (supported by the upper ridging outflow) in the wake of Barbara...and any Bay of Campeche or western Caribbean tropical cyclone development (after Barbara is gone) in such a scenario would be slow to occur. Regardless of development...any lingering surface tropical low activity over SE Mexico and Central America could cause risk of floods and mudslides.

Area # 2....Thunderstorm cluster moving across the Bahamas....

No changes with this system since special update #1B except that the strongest part of the cluster is presently just east-northeast of the Bahamas. The latent heat release of the thunderstorms has inflated upper ridging just ahead of the supporting upper trough...seemingly reducing the southwesterly shear ahead of the upper trough. However...their are no signs of surface pressure falls as the SW quad of the Atlantic surface ridge continues dominating here. See special update #1B for details on how this system could continue to evolve in the next 30 hours.

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2013 Atlantic Hurricane Season Birdseye Discussion #1C (Special Update)

By: NCHurricane2009, 1:32 PM GMT on May 30, 2013

...THURSDAY MAY 30 2013...9:32 AM EDT...
The following is an update to the two areas of interest in the Atlantic basin highlighted in special update #1B early this morning...

Area # 1....Update on Eastern Pacific Tropical Depression Barbara....

While continuing to be pulled northward between the flow of the low-level Atlantic subtropical ridge and central US frontal system...Barbara has continued across southeastern Mexico and is about to emerge into the Atlantic Basin from the Bay of Campeche...but has weakened into a tropical depression due to landfall in Mexico. Given a recent burst of storms on the north half of the circulation and the fact the system is still below favorable tropical upper ridging...I now forecast Barbara will enter the Bay of Campeche as a tropical depression later today. As such...the NHC would maintain advisories while still calling it Tropical Depression Barbara...but whether or not she retains her eastern Pacific name I still plan on issuing a full birdseye discussion with a Barbara forecast later today if Barbara is still a tropical depression in the Bay of Campeche by this afternoon. Afterwards...I forecast in the next 24 hours that the tropical depression will continue northward out of the Bay of Campeche and into the southwest Gulf of Mexico and get ripped apart by westerly vertical shear north of the tropical upper ridging.

With model runs showing tropical upper ridging persisting over Central America...SE Mexico...and over the Bay of Campeche...also wathcing for sustenance of a quasi-stationary broad surface tropical low (supported by the upper ridging outflow) in the wake of Barbara...and any Bay of Campeche tropical cyclone development (after Barbara is gone) in such a scenario would be slow to occur. Regardless of development...any lingering surface tropical low activity over SE Mexico and Central America could cause risk of floods and mudslides.

Area # 2....Thunderstorm cluster moving across the Bahamas....

No changes with this system since special update #1B except that the strongest part of the cluster is presently just east-northeast of the Bahamas. The latent heat release of the thunderstorms has inflated upper ridging just ahead of the supporting upper trough...seemingly reducing the southwesterly shear ahead of the upper trough. However...their are no signs of surface pressure falls as the SW quad of the Atlantic surface ridge continues dominating here. See special update #1B for details on how this system could continue to evolve in the next 36 hours.

Updated: 12:37 AM GMT on May 31, 2013

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2013 Atlantic Hurricane Season Birdseye Discussion #1B (Special Update)

By: NCHurricane2009, 4:14 AM GMT on May 30, 2013

...THURSDAY MAY 30 2013...12:15 AM EDT...
Even though Atlantic Hurricane Season does not officially start until this Saturday June 1...watching a couple of areas tonight. However...neither area shows risk of tropical development at this time...so I am just releasing this special update rather than a discussion.

Area # 1....Update on Eastern Pacific Tropical Storm Barbara....

Over the last 48 hours...eastern Pacific Hurricane Barbara spun up from a broad tropical surface low supported buy favorable outflow of tropical upper ridging. While pulled northward between the flow of the low-level Atlantic subtropical ridge and central US frontal system...Barbara has made landfall in southeastern Mexico...has weakened into a tropical storm...and is soon to weaken into a remnant low.

Over the next 48 hours the low-level flow continues to support a northward track into the Bay of Campeche and western Gulf of Mexico...but a continued northward track would take Barbara's remnant low into hostile westerly shear north of the tropical upper ridging such that the remnant low gets destroyed. With model runs showing tropical upper ridging persisting over Central America...SE Mexico...and over the Bay of Campeche...an alternative scenario is sustenance of a quasi-stationary broad surface tropical low (supported by the upper ridging outflow) in the wake of Barbara...and any Bay of Campeche tropical cyclone development from such a scenario would be slow to occur. Regardless of development...as the current NHC forecast discussion on Barbara states...lingering surface tropical low activity over SE Mexico and Central America could cause risk of floods and mudslides.

Area # 2....Thunderstorm cluster moving across the Bahamas and Cuba....

In addition to Barbara...over the last 48 hours...a southern stream upper trough swept up moisture from the broad tropical low from which Barbara developed...and eastern divergence of the upper trough has supported a thunderstorm cluster that has traveled across the western Caribbean...Cuba...and into the Bahamas. This favorable upper divergence has been exacerbated by the split between southwesterlies ahead of the upper trough and northerlies around the east flank of the tropical upper ridging. Unfavorable factors include high surface pressures on the SW quad of Atlantic low-level ridging and westerly shear ahead of the upper trough.

For the next 48 hours...tonight's 18Z GFS model shows the south end of the upper trough de-amplify and dissipate over the Bahamas due to northward expansion of tropical upper ridging...with the remainder of the upper trough becoming a Bermuda-area upper vortex. Perhaps split flow upper divergence between westerlies (on south side of Bermuda-area upper vortex) and northerlies (around east flank of tropical upper ridging) could support a continuation of the thunderstorm cluster over the Bahamas...but under such a scenario northwesterly shear would be too high for development unless a portion of this thunderstorm cluster builds below the east flank of the tropical upper ridging in which case shear directly below the upper ridge would be less. Their is no current computer model support for development...for instance at best the 18Z GFS model shows a weak surface trough embedded in the SW quad of the Atlantic ridge. Regardless...any areas that experience persistent rains in this thunderstorm cluster could see some flooding.

Elsewhere with this system...subtropical development in the open western Atlantic associated with eastern divergence of the forecast Bermuda upper vortex will not be possible with high surface pressures on the SW quad of the low-level Atlantic ridge.

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2013 Atlantic Hurricane Season Birdseye Discussion #1A (Special Update)

By: NCHurricane2009, 6:22 AM GMT on May 12, 2013

...SUNDAY MAY 12 2013...2:30 AM EDT...
Although the subtropical disturbance north of Puerto Rico gained a closed surface low yesterday afternoon and continued to have organized thunderstorms northeast of center...vertical wind shear has increased as forecast in the special feature section of discussion #1. Therefore any additional development with this system is not expected...and I have discontinued full birdseye discussions on my blog until Atlantic Hurricane Season starts in June...or until another pre-season disturbance develops.

As promised in my final 2012 hurricane season birdseye discussion back in December...I still plan to release post-storm reports for the 2012 Atlantic Hurricane Season which will include an evaluation of how my storm forecasts (issued on these birdseye discussions) compared with that of the official forecasts from the National Hurricane Center.

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2013 Atlantic Hurricane Season Birdseye Discussion #1

By: NCHurricane2009, 7:17 AM GMT on May 11, 2013

...SATURDAY MAY 11 2013...3:20 AM EDT...
Due to quick organization of a subtropical disturbance north of Puerto Rico this evening into this early morning...I am releasing my first full birdseye discussion of the 2013 Atlantic Hurricane Season even though the season does not officialy start until June 1. See special feature section below for details on this disturbance.

Concept of my birdseye discussions is to analyze the entire Atlantic basin from two maps that provide a "birdseye" view of the region as can be seen below. In 2012 I released a total of 169 such discussions on a daily to near-daily basis during the hurricane season...and also during out-of-season disturbances such as what we have this early morning.

As promised in my final 2012 hurricane season birdseye discussion...I still plan to release post-storm reports for the 2012 Atlantic Hurricane Season which will include an evaluation of how my storm forecasts (issued on these birdseye discussions) compared with that of the official forecasts from the National Hurricane Center.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z, and the 0117Z-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...

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...WESTERN ATLANTIC SUBTROPICAL DISTURBANCE....
Since May 8..Hovmoller Diagrams from the National Hurricane Center (http://www.nhc.noaa.gov/tafb_latest/gehov2latest. gif) showed a tremendous increase in thunderstorms in the western Atlantic north of the Caribbean Islands...associated with eastern divergence supplied by the south end of what is currently the upper trough mentioned in paragraph P3 below. A small upper vortex has fractured from the south end of this upper trough at a location north of Puerto Rico. This upper vortex appears to have locally reduced the westerly vertical shear...and its eastern divergence currently supports a surface trough and impressively-organizing comma-shaped thunderstorm mass.

After consulting computer model runs...it appears that in the next 48 hours the small upper vortex is supposed to de-amplify as SE US upper ridge (in paragraph P2) pushes in from the west. That means if this surface trough stays vertically coupled with the upper vortex...the de-amplification of the upper vortex alone will begin to increase the westerly vertical shear over the surface trough. To make the shear worse...it appears this surface trough will not be moving east with the de-amplifying upper vortex as it gets blocked by 1035 mb ridge center (paragraph P4)...so the surface trough will get bombarded by westerly shear from the incoming SE US upper ridge. Even though the shear is expected to increase in the next 48 hours...I have made this a special feature on my blog this morning because I believe their is a chance of a quick subtropical or tropical cyclone from this system before that time based on the rate of organization we have seen from this system in the past hours.

...WEST-TO-EAST DISCUSSION...
P1...Eastern divergence of upper trough diving in from western Canada supports 1010 mb surface frontal cyclone seen in upper-left of above atmo birdseye chart. Surface front extending from the 1010 mb center reaches into western US.

P2...Upper trough is currenty over central US...with its eastern divergence supporting a surface front from Texas to the Great Lakes. Lowest surface pressure along the front is 1006 mb over the Great Lakes. Warm air advection ahead of the front supports upper ridge over the SE US.

P3...Upper trough currently over the western Atlantic and Atlantic Canada was formerly a cut-off upper vortex over the SE US that produced a prolonged period of unsettled weather in that region over the past week. Now the northern end of this upper trough supports 1010 mb frontal depression south of Greenland with its eastern divergence and 1028 mb surface ridge over eastern Canada with its western convergence. Southern end of this upper trough has fractured into an amplified but small upper vortex north of Puerto Rico associated with a subtropical disturbance that has become quickly organized (see above special feature section for details).

P4...Upper ridge dominates the open Atlantic...with its eastern convergence supporting surface 1035 mb ridge center just NW of the Azores this morning.

P5...Upper vortex currently south of the Azores is cut-off to the southeast of amplified upper ridge axis mentioned in paragraph P4. Its eastern divergence supports pockets of clouds and surface 1018 mb low currently positioned SSW of the Azores.

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