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Tropical Storm Beta Forecast Discussion Number 14
2020-09-21 04:47:08| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Sun Sep 20 2020 000 WTNT42 KNHC 210247 TCDAT2 Tropical Storm Beta Discussion Number 14 NWS National Hurricane Center Miami FL AL222020 1000 PM CDT Sun Sep 20 2020 Satellite and radar imagery shows that the deep convection associated with Beta has decreased considerably since this afternoon. This appears to be the result of dry air entrainment and vertical wind shear. Despite the recent decrease in convective organization, an Air Force Reserve Hurricane Hunter aircraft has found SFMR winds of around 45 kt, and there have been a couple of ship observations this evening of winds of 45-50 kt. Therefore, the initial intensity of 50 kt has been maintained. Data from the most recent center dropwindsonde indicate that the pressure is around 995 mb. Beta is forecast to remain within an area of moderate vertical wind shear, and that along with intrusions of dry air are likely to prevent Beta from strengthening before it nears the Texas coast. As a result, the NHC intensity forecast shows little change in strength before landfall in about 24 hours. Gradual weakening should occur after the center moves over land, but the weakening rate may be slower-than-normal as a portion of the circulation will remain offshore. In 2-3 days, the system is expected to weaken to a tropical depression, and it should become a remnant low by 96 h as it move farther inland over the lower Mississippi Valley. The NHC intensity forecast is near the upper-end of the intensity guidance through 24 hours, and is in best agreement with the SHIPS statistical model. Beta has jogged westward this evening, but the longer-term motion estimate is 290/5 kt. There is once again no change the previous track forecast philosophy. The tropical storm is located between a mid-level ridge over Florida and another ridge over the Southern Plains. Beta should move slowly west-northwestward toward the coast of Texas during the next 12 to 24 hours. After that time, the ridge over the Plains should weaken allowing the ridge to the east to steer Beta northward, and then northeastward near the Upper-Texas coast by mid-week. With the recent westward jog, the new track forecast has been nudged slightly south of the previous track through 24 hours, but is slightly east of the previous advisory thereafter to be closer to the various consensus aids. Key Messages: 1. The expected slow motion of Beta will produce a long duration rainfall event from the middle Texas coast to southern Louisiana. Flash, urban, and river flooding is likely. Rainfall will also spread northward into the ArkLaTex region and east into the Lower Mississippi Valley where flash, urban, and 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 are occurring along portions of the northwestern Gulf Coast within the tropical storm warning area in Louisiana. These winds will spread westward to the Texas coast overnight and Monday. FORECAST POSITIONS AND MAX WINDS INIT 21/0300Z 27.6N 94.5W 50 KT 60 MPH 12H 21/1200Z 28.0N 95.4W 50 KT 60 MPH 24H 22/0000Z 28.5N 96.4W 45 KT 50 MPH 36H 22/1200Z 28.8N 96.7W 35 KT 40 MPH...INLAND 48H 23/0000Z 29.1N 96.2W 30 KT 35 MPH...INLAND 60H 23/1200Z 29.5N 95.2W 30 KT 35 MPH...INLAND 72H 24/0000Z 30.1N 94.0W 30 KT 35 MPH...INLAND 96H 25/0000Z 31.9N 91.6W 20 KT 25 MPH...POST-TROP/INLAND 120H 26/0000Z...DISSIPATED $$ Forecaster Brown
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