764
WTNT42 KNHC 191538
TCDAT2

Tropical Storm Beta Discussion Number 8...Corrected
NWS National Hurricane Center Miami FL AL222020
1000 AM CDT Sat Sep 19 2020

Corrected 96 and 120 h intensities

Morning visible imagery indicates that Beta has become significantly
sheared, with the low-level center mostly exposed well to the
southwest of the main convective area. A new convective band is
currently forming near the center over the northwestern quadrant.
An Air Force Reserve Hurricane Hunter aircraft reported pressures
near 994-995 mb, along with flight-level and SFMR winds that justify
keeping the initial intensity at 50 kt.

The storm appears to be starting its westward turn, and the initial
motion is now 315/3. The mid- to upper-level trough over the
northwestern Gulf of Mexico is lifting out, with a mid-level ridge
building to the north of Beta. This should cause the storm to turn
more westward during the next 6-12 h. After that, a slow west-
northwestward to northwestward motion should develop, with the
center now forecast to be near or over the middle Texas coast in
about 72 h. Beyond 72 h, another mid-latitude trough moving
through the central United States should cause Beta to recurve
slowly to the northeast. The new NHC forecast is shifted a little
to the west and now explicitly shows landfall on the Texas coast in
about 72 h. This new forecast is a little to the north of the
consensus models through 72 h and close to them after that time.

There are lots of uncertainties in the intensity forecast. First,
the global models suggest that the ongoing southwesterly shear may
not subside that much even though the first trough is lifting out.
Second, GOES-16 air mass imagery shows abundant upper-level dry air
over the western Gulf of Mexico, including near the storm center.
Third, surface observations show a drier low-level airmass in place
over southeastern Texas, and some of this may get entrained into the
storm. The intensity guidance has trended downward to the point
where none of the models are currently forecasting Beta to become a
hurricane. Based on this and the current storm structure, the
intensity forecast has been adjusted to show little change in
strength today, followed by slow strengthening to a hurricane by
48-60 h. However, this forecast is well above the guidance, and
additional downward adjustments may be needed later today.

A Tropical Storm Warning is being issued for parts of the Texas and
Louisiana coasts at this time. A Hurricane Warning could still be
issued later today or tonight depending on later intensity
forecasts.

Key Messages:

1. The expected slow motion of Beta has the potential to produce a
long duration rainfall event along the western Gulf Coast. The
potentially prolonged period of rainfall could cause flash, urban,
and river flooding, especially where tide levels are above normal.

2. Life-threatening storm surge and hurricane-force winds are
possible along portions of the northwestern Gulf Coast, with
tropical storm conditions expected by late this weekend. Storm Surge
and Hurricane watches and Tropical Storm warnings are in effect, and
residents in these areas should ensure they have their hurricane
plan in place and follow advice given by local officials.


FORECAST POSITIONS AND MAX WINDS

INIT 19/1500Z 26.6N 92.6W 50 KT 60 MPH
12H 20/0000Z 26.9N 93.0W 50 KT 60 MPH
24H 20/1200Z 27.1N 93.8W 55 KT 65 MPH
36H 21/0000Z 27.5N 94.8W 60 KT 70 MPH
48H 21/1200Z 27.8N 95.5W 65 KT 75 MPH
60H 22/0000Z 28.2N 96.2W 65 KT 75 MPH
72H 22/1200Z 28.6N 96.2W 55 KT 65 MPH...INLAND
96H 23/1200Z 29.5N 95.0W 45 KT 50 MPH...INLAND
120H 24/1200Z 30.5N 93.0W 30 KT 35 MPH...INLAND

$$
Forecaster Beven
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