Issued at 400 AM CDT Sat Sep 19 2020


000
WTNT42 KNHC 190853
TCDAT2
 
Tropical Storm Beta Discussion Number   7
NWS National Hurricane Center Miami FL       AL222020
400 AM CDT Sat Sep 19 2020
 
Beta has generally changed little overnight.  The storm is still
quite asymmetric due to southwesterly wind shear with the low-level
center located near the southwestern edge of the main area of deep
convection. An ASCAT pass from a few hours ago showed peak winds in
the 40-45 kt range, with most of the tropical-storm-force winds on
the north side of the circulation. In addition, the latest Dvorak
classifications are 3.0/45 kt from TAFB and SAB. The initial
intensity of 50 kt, based on the earlier aircraft data, is a little
above the satellite estimates.  The Air Force Hurricane Hunters are
scheduled to investigate Beta again later this morning, and the data
they collect will provide a better estimate of the intensity and
structure of the storm.
 
Beta is moving northward, with the latest initial motion estimated 
to be 360/7 kt.  The shortwave trough that has been causing the 
north to northeastward motion during the past day or so is moving 
away and a weak mid-level ridge is expected to build to the north of 
the storm soon.  This change in the steering pattern should cause 
Beta to turn westward and slow down later today and then move 
generally westward to northwestward through the remainder of the 
weekend and into early next week.  This motion should take Beta 
toward the Texas coast by Monday. Around the time Beta is forecast 
to be near the Texas coastline, the ridge is expected to retreat as 
another shortwave trough approaches, which should cause the storm to 
slow down even more and gradually turn to the northeast near the 
Texas coast by the middle of next week.  The models are in fair 
agreement, and the NHC track forecast lies close to the various 
consensus aids.
 
As mentioned above, the tropical storm is still feeling some
effects of southwesterly wind shear, but the upper-level pattern is
expected to become more favorable for strengthening later today.
Although the shear is expected to lessen, water vapor images show a
swath of dry air approaching the storm from the west.  Based on
these mixed environmental conditions, slow strengthening is
forecast during the next couple of days and Beta is forecast to
reach hurricane intensity in about 36 hours.  Beyond a few days,
the models suggest that there could be another increase in
southwesterly shear, which in combination with land interaction
should cause some weakening.  Of course, the rate of weakening will
depend on whether Beta is inland or offshore.  The NHC intensity
forecast is largely an update of the previous one and lies at the
high end of the model guidance.
 
Key Messages:
 
1. 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.
 
2. Life-threatening storm surge and hurricane-force winds are
possible along portions of the Texas coast early next week, with
tropical storm conditions possible by late this weekend. Storm Surge
and Hurricane watches 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  19/0900Z 26.0N  92.5W   50 KT  60 MPH
 12H  19/1800Z 26.6N  92.6W   55 KT  65 MPH
 24H  20/0600Z 26.9N  93.4W   60 KT  70 MPH
 36H  20/1800Z 27.1N  94.3W   65 KT  75 MPH
 48H  21/0600Z 27.4N  95.2W   70 KT  80 MPH
 60H  21/1800Z 27.7N  95.9W   70 KT  80 MPH
 72H  22/0600Z 28.1N  96.3W   65 KT  75 MPH
 96H  23/0600Z 28.7N  95.4W   60 KT  70 MPH
120H  24/0600Z 29.7N  93.3W   50 KT  60 MPH
 
$$
Forecaster Cangialosi