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Tropical Storm Beta Discussion Number  16
NWS National Hurricane Center Miami FL       AL222020
1000 AM CDT Mon Sep 21 2020
 
There has been little change in Beta's overall convective structure 
and intensity, with thunderstorm activity pulsing near the center 
while the outer rain bands have changed little and keep rotating 
onshore the central and upper Texas coastal areas. Dry air 
intrusions into the inner-core region have continued to prevent 
Beta from strengthening by eroding the central dense overcast 
(CDO). The initial intensity of 45 kt is based on data from an Air 
Force Reserve reconnaissance aircraft showing peak SFMR surface 
winds of 40-45 kt and maximum flight-level winds of 50 kt so far, 
along with a dropsonde-measured central pressure of 996-997 mb.
 
Beta now appears to be moving west-northwestward at a slightly 
faster forward speed, with the initial motion estimated to be 290/06 
kt based on data from the aircraft and NOAA Doppler radars from 
Corpus Christi and Houston, Texas. The forecast discussion is the 
same old song as it was 24 hours ago with Beta expected to move just 
inland over the central Texas coastal Plain in about 12-18 hours, 
followed by a sharp decrease in motion, possibly resulting in Beta 
stalling for a few hours as steering currents collapse. A trough to 
the west combines with a broad ridge to the east located over the 
Gulf of Mexico to begin nudging Beta slowly northeastward or 
east-northeastward in 24-36 hours, followed by a slightly faster 
forward speed on days 3 and 4, which will continue until the cyclone 
dissipates over Mississippi by day 5. The new NHC track forecast is 
essentially just an update of the previous advisory track, keeping
Beta just inland or near the Texas coast through 60 hours, a 
scenario that is close to the various consensus models, and which 
lies between the more westward-and-inland ECMWF solution and the 
more eastward-and-overwater GFS track forecast. 

West-southwesterly vertical wind shear of 15-20 kt is not only 
expected to keep Beta's track close to the coastline, but it will 
also affect the cyclone's intensity along with land interaction. 
The closer the cyclone stays near the Gulf of Mexico, the more 
likely that bands of convection containing tropical-storm-force 
winds will continue to roll onshore the Texas coast through 36-48 
hours. Given that the models over the past 24 hours have been 
trending toward a track closer to the coast, the NHC official 
intensity remains unchanged from the previous advisory, and lies a 
little above all of the available guidance through 48 hours.

Key Messages:
 
1. The expected slow motion of Beta will produce a long duration
rainfall event from the middle Texas coast to southeast Louisiana.
Flash, urban, and minor river flooding is likely. Rainfall will also
spread northward into the ArkLaTex region and east into the Lower
Mississippi Valley and portions of the Southeast through the end of
the week. Flash, urban, and isolated minor river flooding is
possible.
 
2. There is the danger of life-threatening storm surge near times of
high tide through Tuesday along portions of the Texas and Louisiana
coasts within the storm surge warning areas. Residents in these
areas should follow advice given by local officials.
 
3. Tropical-storm-force winds will spread westward across the Texas
coast later this morning and continue into Tuesday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 27.9N  95.7W   45 KT  50 MPH
 12H  22/0000Z 28.3N  96.5W   45 KT  50 MPH...NEAR TEXAS COAST
 24H  22/1200Z 28.5N  96.7W   40 KT  45 MPH...INLAND
 36H  23/0000Z 28.8N  96.3W   35 KT  40 MPH...INLAND
 48H  23/1200Z 29.1N  95.3W   30 KT  35 MPH...NEAR TEXAS COAST
 60H  24/0000Z 29.7N  94.0W   25 KT  30 MPH...NEAR TEXAS COAST
 72H  24/1200Z 30.8N  92.5W   25 KT  30 MPH...INLAND
 96H  25/1200Z 33.5N  89.8W   20 KT  25 MPH...POST-TROP/INLAND
120H  26/1200Z...DISSIPATED INLAND
 
$$
Forecaster Stewart
 
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