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Tropical Storm Beta Discussion Number  15
NWS National Hurricane Center Miami FL       AL222020
400 AM CDT Mon Sep 21 2020
 
Beta is struggling this morning.  Satellite images show that
much of the deep convection associated with the storm has
dissipated, and data from the Air Force Hurricane Hunters indicate
that the winds have decreased.  Based on a combination of
flight-level and SFMR data from the aircraft, the initial intensity
is lowered to 45 kt.  This estimate is also in agreement with an
ASCAT pass from a few hours ago that showed peak winds close to 40
kt.  It is also worth noting that the tropical-storm-force winds
are largely confined to the northern half of the circulation, and
these winds should spread across the Texas coast later this morning.
 
Beta has been moving due westward during the past several hours,
with the latest initial motion estimated to be 270/5 kt. In the
short term, Beta is expected to resume a west-northwestward motion
at a forward speed of about 5 kt, and that motion should take the
tropical storm to the Texas coast by tonight. The models differ on
how far inland Beta gets over Texas, but the majority of the
guidance shows the cyclone stalling just inland on Tuesday in weak
steering currents.  The combination of an approaching shortwave
trough and an amplifying ridge over Florida should cause Beta to
turn northeastward along or near the Texas coast late Tuesday  
and Wednesday, and then farther inland over Louisiana on Thursday.  
The NHC track forecast is largely an update of the previous one and
remains near the various consensus aids.
 
The tropical storm is certainty feeling the effects of dry and
stable air that has wrapped into the circulation.  The combination
of the dry air mass and 15-20 kt of southwesterly wind shear should
limit strengthening through landfall tonight.  Steady weakening
is forecast after that time due to the storm interacting with land
and stronger southwesterly shear.  The models are in quite good
agreement, and the NHC intensity forecast lies near the high
end of the guidance envelope.
 
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  21/0900Z 27.7N  95.1W   45 KT  50 MPH
 12H  21/1800Z 28.0N  96.0W   45 KT  50 MPH
 24H  22/0600Z 28.4N  96.6W   40 KT  45 MPH...INLAND
 36H  22/1800Z 28.7N  96.5W   35 KT  40 MPH...INLAND
 48H  23/0600Z 28.9N  95.8W   30 KT  35 MPH...INLAND
 60H  23/1800Z 29.4N  94.7W   25 KT  30 MPH...INLAND
 72H  24/0600Z 30.2N  93.2W   25 KT  30 MPH...INLAND
 96H  25/0600Z 32.8N  90.5W   20 KT  25 MPH...POST-TROP/INLAND
120H  26/0600Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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