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Tropical Storm Beta Forecast Discussion Number 7
2020-09-19 10:54:01| National Hurricane Center (Atlantic)
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
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