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Tropical Depression Beta Forecast Discussion Number 20
2020-09-22 16:59:06| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Tue Sep 22 2020 000 WTNT42 KNHC 221458 TCDAT2 Tropical Depression Beta Discussion Number 20 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Tue Sep 22 2020 High-resolution visible satellite imagery, surface observations, and NOAA Doppler weather radar data from San Antonio, Corpus Christi, and Houston, Texas, indicate that Beta has moved a little farther inland and has weakened to a tropical depression. The same data also show that Beta has started a slow drift toward the northeast. Deep convection has waned considerably since the previous advisory, especially during the past few hours, with cloud tops now warmer than -30 deg C, which no longer meets the Dvorak satellite classification criterion. The initial intensity is 30 kt is based on average Doppler velocities of 35-40 kt between 1500-2500 ft ASL just to the southeast and south of Galveston. The initial motion estimate is now 045/02 kt. Steering currents around Beta remain weak. However, water vapor imagery indicates that a broad mid- to upper-level trough over western Texas is moving slowly eastward, and that feature should gradually force Beta east-northeastward later today and tonight, followed by a faster motion toward the northeast on Wednesday and Thursday across Louisiana and Mississippi before dissipating in about 4 days. The new NHC forecast track is similar to the previous advisory track, which keeps Beta just inland from the Gulf coast, and lies near a blend of the simple consensus models TVCA and GFEX, and the NOAA corrected-consensus model HCCA. Since Beta's center is forecast to remain just inland for the next 36-48 hours, chances of the cyclone regaining tropical storm status are becoming less likely. As a result, the new official intensity forecast shows Beta remaining a 25-30 kt depression during that time, followed by weakening to a remnant low by 48 hours, and dissipation over Mississippi or Alabama by 96 hours. This is consistent with the various simple and corrected-consensus models. Although Beta is now an inland tropical depression, the National Hurricane Center will continue to issue advisories on the cyclone due to its proximity to the Gulf of Mexico and until it becomes clear that re-strengthening into a tropical storm is unlikely. Key Messages: 1. Significant flash and urban flooding is occurring and will continue for the middle and upper Texas coast today. The slow motion of Beta will continue to produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and minor to isolated moderate river flooding is likely. Periods of rainfall will spread 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 on smaller rivers. 2. Persistent onshore flow will continue to result in above normal high tides, and coastal flooding over the next few days will be slow to recede. For information on the ongoing coastal flooding, please refer to coastal flood products issued by local National Weather Service offices. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 28.9N 96.7W 30 KT 35 MPH...INLAND 12H 23/0000Z 29.0N 96.3W 30 KT 35 MPH...INLAND 24H 23/1200Z 29.6N 95.1W 30 KT 35 MPH...INLAND 36H 24/0000Z 30.4N 93.7W 25 KT 30 MPH...INLAND 48H 24/1200Z 31.7N 92.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 25/0000Z 33.1N 90.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 25/1200Z 34.4N 88.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 26/1200Z...DISSIPATED INLAND $$ Forecaster Stewart
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Category:Transportation and Logistics