2015 Atlantic Hurricane Season Birdseye Discussion #22

By: NCHurricane2009 , 6:59 AM GMT on June 15, 2015

...MONDAY JUNE 15 2015 2:59 AM EDT...
A subtropical or tropical storm could form in the western Gulf of Mexico from disturbance Invest 91-L at any time as aircraft reconaissance from this past afternoon indicated storm force winds and the formation of a surface circulation. See special feature section below for additional details on this developing situation. Additional heavy weather is possible across Guatemala...Belize...and the Yucatan Peninsula of southeastern Mexico over the next 24 hours. Because this system is only 2 to 3 days from affecting eastern Texas and western Louisiana...tropical storm advisories could be hoisted for these areas should this system be upgraded later today.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0121Z-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.


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at http://www.nhc.noaa.gov/satellite.php...the site from which the above thermo chart is generated from...are currently outdated.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).

Current prognosis...As of 0000Z the National Hurricane Center TAFB analyzed the location of the 1007 mb surface low of Invest 91-L to be at 23N-91W. The surrounding shower and thunderstorm activity has become much better organized relative to 24 hrs ago...but this system maybe more subtropical than tropical as the surface low is currently stacked below its parent upper vortex. Because the 0000Z TAFB fix on Invest 91-L is 1N-0.5W off from where I predicted in the previous discussion...I have adjusted my track forecast points below by 1N-0.5W accordingly. I am maintaining the intensity forecast from the previous discussion since this system is already producing storm force winds according to last afternoon's aircraft reconaissance mission.

Atmospheric Outlook for the Forecast Period...This system is expected to track northwestward and then curve northward toward eastern Texas while rounding the west side of the Atlantic surface subtropical ridge (marked by red zig-zag line in the above atmospheric features chart). On this track...it will be escaping the weakening overhead upper vortex and move into more favorable upper winds below an adjacent upper ridge (presently marked by blue H over the Louisiana coast). As it moves away from its cold core upper vortex and below the warm core upper ridge...this will give opportunity for this system to look less subtropical and more tropical.

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 overheadupper 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 continue to weaken...currently not expecting dry air to be an issue for this system's development.

24 Hr Forecast (0000Z Jun 16)...50 mph max sustained wind tropical storm centered in the western Gulf of Mexico at 25.5N-93.5W

48 Hr Forecast (0000Z Jun 17)...65 mph max sustained wind tropical storm making landfall on the eastern Texas coast centered at 28.7N-96W

72 Hr Forecast (0000Z Jun 18)...Remnant low centered over northeastern Texas at 32.5N-96.5W

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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