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Tropical Storm Beta Discussion Number   5
NWS National Hurricane Center Miami FL       AL222020
400 PM CDT Fri Sep 18 2020

Satellite imagery indicates that the circulation of Tropical 
Depression 22 has become better defined, and most objective and 
subjective satellite intensity estimates are now 35 kt.  Based on 
this, along with 33 kt 1-mi average winds from NOAA buoy 42002, the 
depression is upgraded to Tropical Storm Beta with an initial 
intensity of 35 kt.  Although the system is now a tropical storm, 
satellite imagery shows that the convective pattern is becoming 
elongated due to the effects of southwesterly vertical wind shear.

Visible imagery and scatterometer data showed that the center of 
Beta was a bit farther east than previously thought, and the initial 
motion is a somewhat uncertain 025/8.  This motion should continue 
for the next 12-24 h as the storm is steered by a mid- to 
upper-level trough over Texas and northeastern Mexico.  After that 
time, the trough should weaken and lift out to the northeast, with a 
mid-level ridge building to the north of the cyclone above an 
already present low-level ridge.  This ridge should act as a Beta 
blocker, causing the storm to turn westward toward the western Gulf 
coast.  Between 72-120 h, the mid-level ridge weakens as another 
mid-latitude trough moves through the central United States, and 
this is expected to cause the storm to slowly recurve toward the 
northeast.  One change in the track guidance since the previous 
forecast is that the GFS and ECMWF are a bit faster on the westward 
motion and show the center near the Texas coast in about 72 h.  The 
latter part of the new track forecast also shifts westward, but it 
is still to the east of the GFS/ECMWF.  There is also a chance that 
Beta could move more northward than forecast before the trough lifts 
out, which adds an additional touch of uncertainty to the track 
forecast.  So, it is critical that users not focus on the exact 
forecast track, especially at days 3 to 5.

The global models suggest that the current shear may decrease a 
little after 24 h when the upper-level trough moves away from Beta. 
However, there is a chance of at least some dry air entrainment 
that would hamper strengthening.  The intensity guidance for the 
most part continues to forecast Beta to reach a peak intensity 
below hurricane strength, although the latest SHIPS model forecasts 
a peak intensity near 65 kt.  The new intensity forecast is again 
unchanged in making Beta a hurricane at 60 and 72 h, and it lies at 
the upper edge of the intensity guidance.

Key Messages:
 
1.  Beta is expected to strengthen and possibly become a hurricane, 
while moving slowly over the western Gulf of Mexico during the next 
few days.
 
2. There is an increasing risk of heavy rainfall and flooding along 
the northwest Gulf Coast Sunday through at least the middle of next 
week as Beta is forecast to move slowly toward and along or offshore 
of the coast through that time. For additional information, see 
products from your local National Weather Service office. 
 
3.  While it is too early to determine what areas could see direct
wind and storm surge impacts from Beta, interests throughout
the western Gulf of Mexico should monitor the progress of this
system and future updates to the forecast. Storm Surge and 
Tropical Storm or Hurricane watches could be issued tonight or 
Saturday.  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/2100Z 24.3N  93.1W   35 KT  40 MPH
 12H  19/0600Z 25.1N  92.9W   40 KT  45 MPH
 24H  19/1800Z 25.9N  93.0W   45 KT  50 MPH
 36H  20/0600Z 26.1N  93.7W   50 KT  60 MPH
 48H  20/1800Z 26.3N  94.6W   60 KT  70 MPH
 60H  21/0600Z 26.5N  95.5W   65 KT  75 MPH
 72H  21/1800Z 26.8N  96.3W   65 KT  75 MPH
 96H  22/1800Z 27.5N  96.5W   60 KT  70 MPH
120H  23/1800Z 28.5N  96.0W   55 KT  65 MPH
 
$$
Forecaster Beven
 
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