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Tropical Storm Beta Discussion Number  17
NWS National Hurricane Center Miami FL       AL222020
400 PM CDT Mon Sep 21 2020
 
Beta's convective cloud structure has continued to erode since the 
previous advisory as cold-air stratocumulus clouds have wrapped 
around the entire and into the system center. Most of the cloud tops 
are barely reaching the freezing level, with the exception of a 
small convective burst that has recently developed near and to the 
northwest of the low-level center. The initial intensity has been 
lowered to 40 kt and is based on data from the last Air Force 
Reserve reconnaissance leg that indicated peak SFMR surface winds 
of 40-42 kt northwest of the center and a dropsonde-measured 
central pressure of 999-1000 mb.
 
The initial motion estimate 310/04 kt. Beta is expected to move 
onshore the central Texas coast later tonight, and then stalling 
along or just inland from the coast during the 12-24 hour period 
when the steering currents collapse due to a complete break down of 
a weak ridge over the Gulf of Mexico. A weak trough to the west of 
the cyclone is then forecast to nudge Beta east-northeastward toward 
the Gulf of Mexico in the 36-60 hour period, with the cyclone 
possibly reaching the warm Gulf waters by 48 hours. By 72 hours and 
beyond, the approaching mid-level trough Beta is expected to move 
Beta a little faster toward the northeast until the cyclone 
dissipates over the Lower Mississippi Valley area by day 5. The 
latest NHC track guidance has shifted a little farther to right or 
east of the previous forecast track, with most of the models now 
taking Beta back out over the western Gulf of Mexico by 24 hours. As 
a result, the new NHC official track forecast has been nudged a 
little farther to the right of the previous, but remains to the 
left or west of the NOAA-HCCA consensus model and the UKMET model.
 
West-southwesterly wind shear of 15-20 kt is expected to affect Beta 
for the next 36 hours or so, followed by a gradual increase in the 
shear thereafter. That unfavorable flow regime, along with land 
interaction, should induce a slow weakening trend throughout the 
forecast period. The NHC intensity forecast remains a little above 
the available model guidance through 48 hours since Beta is forecast 
to remain very close to or over the Gulf of Mexico where convective 
rain bands containing tropical-storm-force winds could possibly move 
onshore the central and upper Texas coastal areas.
 
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 evening and continue into Tuesday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 28.2N  96.1W   40 KT  45 MPH
 12H  22/0600Z 28.5N  96.6W   35 KT  40 MPH...INLAND
 24H  22/1800Z 28.7N  96.5W   35 KT  40 MPH...INLAND
 36H  23/0600Z 28.9N  95.8W   35 KT  40 MPH...NEAR TEXAS COAST
 48H  23/1800Z 29.2N  94.7W   30 KT  35 MPH...OVER WATER
 60H  24/0600Z 29.7N  93.3W   25 KT  30 MPH...OVER WATER
 72H  24/1800Z 30.8N  91.6W   20 KT  25 MPH...INLAND
 96H  25/1800Z 34.1N  88.7W   20 KT  25 MPH...POST-TROP/INLAND
120H  26/1800Z...DISSIPATED INLAND
 
$$
Forecaster Stewart
 
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