2015 Atlantic Hurricane Season Birdseye Discussion #23

By: NCHurricane2009 , 4:52 AM GMT on June 16, 2015

...TUESDAY JUNE 16 2015 12:52 AM EDT...
Invest 91-L has become Tropical Storm Bill and will be making landfall in eastern Texas later today. The largest threat will be flash flooding from heavy rains from Bill and its remnants over the next few days for eastern Texas...eastern Oklahoma...parts of Missouri...northern Illinois...the southern Great Lakes region...and the Ohio Valley. See special feature section below for additional details on Bill. Visit www.nhc.noaa.gov for up to the minute lastest information on Bill including tropical storm warnings.


This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-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at http://www.nhc.noaa.gov/satellite.php...the site from which the above thermo chart is generated from...are currently outdated.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...Tropical surface low Invest 91-L moved northwestward away from its diminishing parent upper vortex in the southwestern Gulf of Mexico and below an upper ridge in the northwestern Gulf of Mexico...allowing this system to further organize into a tropical storm in the low shear and enhanced upper outflow environment of this upper ridge. Maximum sustained winds measured by reconaissance aircraft are currently 50 mph and the storm has about another 12 hours to strengthen before it makes landfall in eastern Texas.

Atmospheric Outlook for the Forecast Period...This system is tracking northwestward and will curve northward into the central United States from eastern Texas...and then will curve northeastward into the southern Great Lakes/Ohio Valley region while rounding the west side of the Atlantic surface subtropical ridge (marked by red zig-zag line in the above atmospheric features chart).

Thermodynamic Outlook for the Forecast Period...Thermodynamic conditions are favorable for additional strengthening of Bill before it makes landfall with sea-surface temperatures in the northwestern Gulf of Mexico above 26 deg C and with Bill well-embedded in a tropical moisture channel that has become established on the west side of the Atlantic subtropical ridge stretching all the way from the western Caribbean Sea thru the central and northeastern US.

Track Forecast...As of 0000Z earlier this evening Bill was about 1N and 0.5W off from where I predicted it would be...so my track forecast in the above graphic is a 1N and 0.5W adjustment of my previous. This track forecast is slightly east of the National Hurricane Center's and makes Bill make landfall sooner than previously anticipated.

Intensity Forecast...The current intensity forecast from the NHC is just slightly below my previous intensity forecasts. Even though Bill has been following my previous intensity forecasts...I agree with a downward adjustment and join the current NHC intensity forecast since Bill will be making landfall sooner.

Impact Forecast...My impact swath in the above forecast graphic is based on extrapolating the 10 PM CDT NHC tropical storm wind field along my forecast track for the portion of the track where Bill is a tropical storm. The ground is still soaked and rivers are still swollen over eastern Texas and the central US due to May's excessive central US rainfall. Moreover the ground over the southern Great Lakes and Ohio Valley region has recently become soaked from frequent rains along the stalled frontal boundary presently over this region. Therefore main threat from Bill and its remnant low will be flash flooding in these regions as outlined in impact statement (c) in the above graphic. Widespread flash flood watches from the National Weather Service are currently in effect in these regions.

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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