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Tropical Storm Beta Forecast Discussion Number 16
2020-09-21 16:51:43| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Mon Sep 21 2020 000 WTNT42 KNHC 211451 TCDAT2 Tropical Storm Beta Discussion Number 16 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Mon Sep 21 2020 There has been little change in Beta's overall convective structure and intensity, with thunderstorm activity pulsing near the center while the outer rain bands have changed little and keep rotating onshore the central and upper Texas coastal areas. Dry air intrusions into the inner-core region have continued to prevent Beta from strengthening by eroding the central dense overcast (CDO). The initial intensity of 45 kt is based on data from an Air Force Reserve reconnaissance aircraft showing peak SFMR surface winds of 40-45 kt and maximum flight-level winds of 50 kt so far, along with a dropsonde-measured central pressure of 996-997 mb. Beta now appears to be moving west-northwestward at a slightly faster forward speed, with the initial motion estimated to be 290/06 kt based on data from the aircraft and NOAA Doppler radars from Corpus Christi and Houston, Texas. The forecast discussion is the same old song as it was 24 hours ago with Beta expected to move just inland over the central Texas coastal Plain in about 12-18 hours, followed by a sharp decrease in motion, possibly resulting in Beta stalling for a few hours as steering currents collapse. A trough to the west combines with a broad ridge to the east located over the Gulf of Mexico to begin nudging Beta slowly northeastward or east-northeastward in 24-36 hours, followed by a slightly faster forward speed on days 3 and 4, which will continue until the cyclone dissipates over Mississippi by day 5. The new NHC track forecast is essentially just an update of the previous advisory track, keeping Beta just inland or near the Texas coast through 60 hours, a scenario that is close to the various consensus models, and which lies between the more westward-and-inland ECMWF solution and the more eastward-and-overwater GFS track forecast. West-southwesterly vertical wind shear of 15-20 kt is not only expected to keep Beta's track close to the coastline, but it will also affect the cyclone's intensity along with land interaction. The closer the cyclone stays near the Gulf of Mexico, the more likely that bands of convection containing tropical-storm-force winds will continue to roll onshore the Texas coast through 36-48 hours. Given that the models over the past 24 hours have been trending toward a track closer to the coast, the NHC official intensity remains unchanged from the previous advisory, and lies a little above all of the available guidance through 48 hours. 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 21/1500Z 27.9N 95.7W 45 KT 50 MPH 12H 22/0000Z 28.3N 96.5W 45 KT 50 MPH...NEAR TEXAS COAST 24H 22/1200Z 28.5N 96.7W 40 KT 45 MPH...INLAND 36H 23/0000Z 28.8N 96.3W 35 KT 40 MPH...INLAND 48H 23/1200Z 29.1N 95.3W 30 KT 35 MPH...NEAR TEXAS COAST 60H 24/0000Z 29.7N 94.0W 25 KT 30 MPH...NEAR TEXAS COAST 72H 24/1200Z 30.8N 92.5W 25 KT 30 MPH...INLAND 96H 25/1200Z 33.5N 89.8W 20 KT 25 MPH...POST-TROP/INLAND 120H 26/1200Z...DISSIPATED INLAND $$ Forecaster Stewart
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