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2015 Atlantic Hurricane Season Birdseye Discussion #21
By: NCHurricane2009 , 6:46 AM GMT on June 14, 2015
...SUNDAY JUNE 14 2015 2:50 AM EDT...
The disturbance over the western Caribbean Sea and Yucatan peninsula of southeastern Mexico...supported by upper divergence on the southeastern flank of the upper vortex in the Gulf of Mexico...continues to become better organized and has been upgraded to Invest 91-L as noted in special update #20A. Upper-level winds are expected to become more favorable for development as this disturbance moves into the western Gulf of Mexico over the next 48 hours as the upper vortex weakens...and therefore their is a high chance of this system becoming a tropical depression or tropical storm. See special feature section below for additional details on this developing situation. Regardless of development...the Yucatan Peninsula of southeastern Mexico can expect heavier weather to conitnue to increase during the next 24 hours...and eastern Texas and western Louisiana can expect the arrival of enhanced tropical moisture by 72 to 96 hours (3 to 4 days).
...ATMOSPHERIC FEATURES BIRDSEYE CHART...
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0128Z-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).
...SPECIAL FEATURE...TROPICAL LOW INVEST 91-L...
Current prognosis...A surface low analyzed at 1007 mb by the National Hurricane Center TAFB is present over the Yucatan Peninsula of southeastern Mexico and is supported by upper divergence on the southeastern quadrant of an upper vortex in the Gulf of Mexico (marked by blue L in the above atmospheric features chart). Visible satellite imagery before sunset and current nighttime infrared satellite imagery show cyclonic turning in the low-level clouds around the surface low...but the thickest clouds containing showers and thunderstorms are biased to the eastern half of the circulation due to westerly shear caused by the upper vortex. Some of the heavy weather in the east half of the circulation has made landfall on the east coast of the Yucatan peninsula...and will continue to overspread the rest of the Yucatan as the surface low pressure center tracks northwest into the Gulf of Mexico during the next 24 hours.
Atmospheric Outlook for the Forecast Period...The upper vortex in the Gulf of Mexico will be weakening thru the forecast period...reducing the vertical shear and allowing this system to progressively become better organized. This system is expected to track northwestward and then curve northward toward eastern Texas while rounding the west side of the Atlantic surface subtropiacl ridge (marked by red zig-zag line in the above atmospheric features chart).
Thermodynamic Outlook for the Forecast Period...Conditions are favorable for development in the context of sea-surface temperatures with all of the Gulf of Mexico presently above 26 deg C. Regarding moisture...the only source of unfavorable dry air will be caused by upper convergence on the west side of the Gulf of Mexico upper vortex. However with the system already featuring a very expansive moisture field in relation to this dry air and with the upper vortex expected to weaken...currently not expecting dry air to be an issue for this system's development.
24 Hr Forecast (0000Z Jun 15)...35 mph max sustained wind tropical depression centered in the Gulf of Mexico just northwest and offshore of the Yucatan Peninsula at 22N-90.5W
48 Hr Forecast (0000Z Jun 16)...50 mph max sustained wind tropical storm centered in the western Gulf of Mexico at 24.5N-93.5W
72 Hr Forecast (0000Z Jun 17)...65 mph max sustained wind tropical storm approaching landfall on the eastern Texas coast centered at 27.7N-95.5W
96 Hr Forecast (0000Z Jun 18)...Remnant low centered over eastern Texas at 31.5N-96W
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.