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Post-Tropical Cyclone Gabrielle Forecast Discussion Number 11
2019-09-06 10:50:36| National Hurricane Center (Atlantic)
Issued at 500 AM AST Fri Sep 06 2019 000 WTNT43 KNHC 060850 TCDAT3 Post-Tropical Cyclone Gabrielle Discussion Number 11 NWS National Hurricane Center Miami FL AL082019 500 AM AST Fri Sep 06 2019 Poorly defined Gabrielle has not produced any organized deep convection since Thursday morning, and what remains of the showers and thunderstorms, is displaced nearly 200 miles north of the elongated surface circulation. Consequently, Gabrielle can no longer be classified as a tropical cyclone and has degenerated into a 35 kt post-tropical cyclone. Statistical-dynamical models, as well as the large-scale guidance, show that strong shear, along with mid-tropospheric dry air intrusion, should continue to inhibit convective development during the next 24 h or so, and cause further weakening into a remnant low. Around mid-period, the shear is forecast to decrease and the upper wind pattern becomes more diffluent. Additionally, Post-Tropical Cyclone Gabrielle will be traversing significantly warmer oceanic sea surface temperatures. As a result, the cyclone is forecast to redevelop organized deep convection, and more than likely, re-strengthen. In fact, some of the intensity guidance shows Gabrielle becoming a hurricane in 4 days before transitioning into an extratropical cyclone at the end of the period. The NHC intensity forecast is based on a blend of the HFIP HCCA, and the deterministic guidance beyond day 3. The initial motion is estimated to be an accelerating northwestward motion, or 315/10 kt. The global and regional models are in rather good agreement that the post-tropical cyclone will gradually turn toward the west-northwest during the next 48 hours, before recurving northward and then northeastward early next week in response to an approaching major shortwave mid-latitude trough from the northwest. The official forecast track is just a little to the left of the previous one, and is very close to the TVCA simple multi-model guidance. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 25.5N 37.6W 35 KT 40 MPH...POST-TROPICAL 12H 06/1800Z 27.1N 39.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 07/0600Z 29.2N 41.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 07/1800Z 30.7N 44.8W 35 KT 40 MPH...TROPICAL CYCLONE 48H 08/0600Z 31.9N 47.4W 45 KT 50 MPH 72H 09/0600Z 35.6N 48.6W 55 KT 65 MPH 96H 10/0600Z 40.4N 44.3W 60 KT 70 MPH 120H 11/0600Z 47.0N 34.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts
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