2015 Atlantic Hurricane Season Birdseye Discussion #15

By: NCHurricane2009 , 3:52 AM GMT on June 08, 2015

...SUNDAY JUNE 7 2015 11:52 PM EDT...
The western Caribbean...Cuba...and Bahamas disturbance has finally developed a surface low...analyzed at 1014 mb in the atmospheric features chart below. Its supporting upper trough in the southeastern Gulf of Mexico has gained a southwest-northeast tilt while merging with the upper trough associated with the 1008 mb frontal depression offshore of the eastern US. This tilting of the upper trough has increased the westerly vertical shear over the disturbance...and therefore this disturbance is not expected to tropically develop as it accelerates northeastward away from the Bahamas and into the open western Atlantic.

Another disturbance is developing in the western Caribbean as a surface trough with showers and thunderstorms has developed under supportive upper divergence on the southeast side of the above-mentioned upper trough in the southeastern Gulf of Mexico. The pair of tropical waves currently in the central Caribbean Sea may add to this disturbance over the next couple of days. As the upper trough also weakens during this time...upper-level winds could become more favorable for the development of this disturbance...especially as it reaches the southern Gulf of Mexico in about 4 days. The CMC computer model has returned to showing this disturbance developing in the Gulf of Mexico...and the latest NAVGEM model seems to suggest the disturbance at least evolving into a tropical low. Upper-level wind forecasts show the southern part of the upper trough associated with the 999 mb north-central US frontal cyclone fracturing into an upper vortex that dives into the western Gulf of Mexico...and therefore any Gulf of Mexico tropical cyclone that develops from this disturbance will likely be of the asymmetric kind that tracks northward on the east side of the upper vortex with all weather biased east of its center while the upper vortex suppresses the weather on its west side.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 2230Z-released WPC analysis.

Features boxed in green...if any...are 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 longer term 5-day outlook.

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. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. 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 temperature isotherms at http://www.nhc.noaa.gov/satellite.php...the site from which the above thermo chart is generated from...are currently outdated. Therfore I have approximated the 26 deg C isotherm in the above chart using the sea-surface temperature maps available at www.wuwnderground.com/tropical. 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).


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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3. WunderAlertBot (Admin)
1:34 AM GMT on June 09, 2015
NCHurricane2009 has created a new entry.
2. Wolfberry
5:01 AM GMT on June 08, 2015
Great write up with explanations.
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1. DeepSeaRising
4:19 AM GMT on June 08, 2015
Very informative, thank you.
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