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Tropical Storm Beta Forecast Discussion Number 5
2020-09-18 22:53:15| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Fri Sep 18 2020 000 WTNT42 KNHC 182053 TCDAT2 Tropical Storm Beta Discussion Number 5 NWS National Hurricane Center Miami FL AL222020 400 PM CDT Fri Sep 18 2020 Satellite imagery indicates that the circulation of Tropical Depression 22 has become better defined, and most objective and subjective satellite intensity estimates are now 35 kt. Based on this, along with 33 kt 1-mi average winds from NOAA buoy 42002, the depression is upgraded to Tropical Storm Beta with an initial intensity of 35 kt. Although the system is now a tropical storm, satellite imagery shows that the convective pattern is becoming elongated due to the effects of southwesterly vertical wind shear. Visible imagery and scatterometer data showed that the center of Beta was a bit farther east than previously thought, and the initial motion is a somewhat uncertain 025/8. This motion should continue for the next 12-24 h as the storm is steered by a mid- to upper-level trough over Texas and northeastern Mexico. After that time, the trough should weaken and lift out to the northeast, with a mid-level ridge building to the north of the cyclone above an already present low-level ridge. This ridge should act as a Beta blocker, causing the storm to turn westward toward the western Gulf coast. Between 72-120 h, the mid-level ridge weakens as another mid-latitude trough moves through the central United States, and this is expected to cause the storm to slowly recurve toward the northeast. One change in the track guidance since the previous forecast is that the GFS and ECMWF are a bit faster on the westward motion and show the center near the Texas coast in about 72 h. The latter part of the new track forecast also shifts westward, but it is still to the east of the GFS/ECMWF. There is also a chance that Beta could move more northward than forecast before the trough lifts out, which adds an additional touch of uncertainty to the track forecast. So, it is critical that users not focus on the exact forecast track, especially at days 3 to 5. The global models suggest that the current shear may decrease a little after 24 h when the upper-level trough moves away from Beta. However, there is a chance of at least some dry air entrainment that would hamper strengthening. The intensity guidance for the most part continues to forecast Beta to reach a peak intensity below hurricane strength, although the latest SHIPS model forecasts a peak intensity near 65 kt. The new intensity forecast is again unchanged in making Beta a hurricane at 60 and 72 h, and it lies at the upper edge of the intensity guidance. Key Messages: 1. Beta is expected to strengthen and possibly become a hurricane, while moving slowly over the western Gulf of Mexico during the next few days. 2. 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. 3. While it is too early to determine what areas could see direct wind and storm surge impacts from Beta, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. Storm Surge and Tropical Storm or Hurricane watches could be issued tonight or Saturday. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 24.3N 93.1W 35 KT 40 MPH 12H 19/0600Z 25.1N 92.9W 40 KT 45 MPH 24H 19/1800Z 25.9N 93.0W 45 KT 50 MPH 36H 20/0600Z 26.1N 93.7W 50 KT 60 MPH 48H 20/1800Z 26.3N 94.6W 60 KT 70 MPH 60H 21/0600Z 26.5N 95.5W 65 KT 75 MPH 72H 21/1800Z 26.8N 96.3W 65 KT 75 MPH 96H 22/1800Z 27.5N 96.5W 60 KT 70 MPH 120H 23/1800Z 28.5N 96.0W 55 KT 65 MPH $$ Forecaster Beven
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