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Tropical Storm Theta Forecast Discussion Number 7
2020-11-11 15:44:29| National Hurricane Center (Atlantic)
Issued at 300 PM GMT Wed Nov 11 2020 000 WTNT45 KNHC 111444 TCDAT5 Tropical Storm Theta Discussion Number 7 NWS National Hurricane Center Miami FL AL302020 300 PM GMT Wed Nov 11 2020 Theta's center continues to be devoid of deep convection, with the convective mass located primarily to the north of the center due to strong shear. A recent partial ASCAT overpass showed a slight decrease in the winds over the eastern semicircle. However, the pass did not sample the western portion of the circulation which has previously had the strongest winds. Based on the slightly lower ASCAT values, and the assumption that the rest of the vortex has spun down slightly due to the lack of convection over the center, the initial intensity is decreased to 50 kt. Theta is moving east-northeastward at 9 kt, steered by the southern part of the mid-latitude westerlies to the north of a mid-level ridge. This steering pattern is expected to remain in place through much of the weekend. By early next week, the ridge is forecast weaken ahead of an approaching mid-latitude trough. This would cause the cyclone to slow its forward motion temporarily before it gets picked up by the trough. The latest NHC forecast is near the previous one through 72 h, and is a little slower during days 4-5 due to the slowing of the guidance. This latest forecast is very near the clustered track consensus models. Despite the strong shear and cool water temperatures, the instability aloft should continue to support deep convection for at least the next few days. The shear is forecast to lessen somewhat in a day or so, but will still be relatively strong. Since the cyclone has been weakening slowly in the current environment, it is anticipated that the pace of weakening may lessen during the next few days with the decrease in shear. Beyond that time, the upper-level winds are forecast to become more northerly, and at about the same time the instability is forecast to decrease. These factors should cause any remaining convection to dissipate, with Theta likely becoming post-tropical by day 5. The latest NHC intensity forecast was adjusted slightly downward from the previous one mainly due to the lower initial intensity and is near the IVCN and HCCA consensus model forecasts. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 29.8N 33.3W 50 KT 60 MPH 12H 12/0000Z 30.3N 31.9W 50 KT 60 MPH 24H 12/1200Z 30.7N 29.7W 45 KT 50 MPH 36H 13/0000Z 31.1N 27.3W 45 KT 50 MPH 48H 13/1200Z 31.5N 25.1W 45 KT 50 MPH 60H 14/0000Z 31.8N 23.2W 45 KT 50 MPH 72H 14/1200Z 31.9N 22.0W 40 KT 45 MPH 96H 15/1200Z 32.2N 20.6W 35 KT 40 MPH 120H 16/1200Z 34.7N 19.2W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Latto
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