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Tropical Storm Beta Forecast Discussion Number 15
2020-09-21 10:42:12| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Mon Sep 21 2020 000 WTNT42 KNHC 210842 TCDAT2 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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Category:Transportation and Logistics