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Tropical Storm Beta Forecast Discussion Number 9
2020-09-19 23:00:42| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sat Sep 19 2020 000 WTNT42 KNHC 192100 TCDAT2 Tropical Storm Beta Discussion Number 9 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Sat Sep 19 2020 Satellite imagery indicates that Beta has a small area of convection over the low-level center, with a dry slot on the northeastern side separating that convection from a larger outer band. Satellite intensity estimates are generally in the 40-55 kt range and have changed little since the past advisory. In addition, a ship just north of the center just reported 47-kt winds and a pressure of 998.6 mb. Based on these data, the initial intensity remains 50 kt. Earlier scatterometer data showed a trough extending from near the center of Beta to just south of the mouth of the Mississippi River, which may be a result of the cyclone's circulation interacting with an old cold front over the northern Gulf. Beta has been nearly stationary since the last advisory, with the center perhaps making a small loop. The guidance is in good agreement that a slow westward to west-northwestward motion should start tonight as a mid-level ridge develops north of the cyclone. A slightly faster west-northwestward motion should then occur through 72 h, bringing the center of Beta near or over the Texas coast in about 60 h. After landfall, a mid-latitude trough moving through the central United States should cause Beta to recurve slowly to the northeast. Despite the current lack of movement, the latest track guidance is a little faster to bring the storm to the coast of Texas with the ECMWF forecasting landfall by 12Z Monday. The new forecast track is a little faster than the previous forecast, but is a little slower than the various consensus models. There remain a lot of uncertainties in the intensity forecast. First, the global models still suggest that the ongoing southwesterly shear may not subside much before landfall. Second, GOES-16 air mass imagery shows abundant upper-level dry air over the western Gulf of Mexico, including near the storm center. Third, surface observations show a drier low-level airmass in place over southeastern Texas, and some of this may be getting entrained into the storm. The intensity guidance has again trended downward, and several of the models now forecast Beta not to strengthen at all as it approaches Texas. Because the sea surface temperatures are warm and the shear is not prohibitively strong, the intensity forecast, while reduced from the earlier forecast, will show slow strengthening to a peak intensity of 60 kt before landfall. This forecast remains above the guidance, and additional downward adjustments may be needed tonight or on Sunday. While the chances that Beta will become a hurricane are decreasing, a Hurricane Warning could still be issued for portions of the Texas coast tonight depending on later intensity trends and forecasts. Key Messages: 1. The expected slow motion of Beta has the potential to produce a long duration rainfall event along the western Gulf Coast. The potentially prolonged period of rainfall could cause flash, urban, and river flooding, especially in coastal areas where tide levels are above normal. 2. There is the danger of life-threatening storm surge near times of high tide from Sunday through Tuesday along portions of the Texas coast within the storm surge warning areas. Residents in these areas should follow advice given by local officials. 3. Tropical storm force winds are expected to begin along portions of the northwestern Gulf Coast by Sunday night within the tropical storm warning area, with hurricane-force winds possible along portions of the Texas coast late Monday and Monday night, where a hurricane watch is in effect. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 26.6N 92.4W 50 KT 60 MPH 12H 20/0600Z 26.7N 93.1W 50 KT 60 MPH 24H 20/1800Z 27.1N 94.0W 55 KT 65 MPH 36H 21/0600Z 27.5N 95.1W 55 KT 65 MPH 48H 21/1800Z 27.9N 96.0W 60 KT 70 MPH 60H 22/0600Z 28.3N 96.4W 60 KT 70 MPH 72H 22/1800Z 28.8N 96.4W 50 KT 60 MPH...INLAND 96H 23/1800Z 29.5N 95.0W 35 KT 40 MPH...INLAND 120H 24/1800Z 31.0N 93.0W 25 KT 30 MPH...INLAND $$ Forecaster Beven
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