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| #981079 (Received by flhurricane at: 5:09 AM 05.Sep.2019) TCDAT3 Tropical Storm Gabrielle Discussion Number 7 NWS National Hurricane Center Miami FL AL082019 500 AM AST Thu Sep 05 2019 METEOSAT imagery and an earlier WindSat microwave overpass show Gabielle`s poorly defined center of circulation sheared well to the south of the curved convective band features to north, indicative of moderate southerly shear. The initial intensity is held at a generous 45 kt for this advisory, and is based on the subjective T-numbers from TAFB and SAB. Although Gabrielle could experience some intensity fluctuations during the next 24 hours, the cyclone should remain in a rather harsh environment during the next 36-48 hours, due to south to southwesterly vertical shear, some dry air in the middle portions of the atmosphere, and oceanic sea surface temperatures on the order of 25-26C. Afterward, gradual strengthening is forecast as Gabrielle moves into a more favorable upper wind pattern and warmer SSTs, and this is consistent with the IVCN multi-model consensus and the Decay SHIPS. After the adjustment to the south of the previous advisory based on the ASCAT-A/B scatterometer passes and a recent SSMI/S image, the initial motion is estimated to be northwestward, or 315/7 kt. For the next several days, Gabrielle is expected to move generally northwestward toward a large weakness in the mid-Atlantic subtropical ridge. An increase in forward motion is expected as the steering flow strengthens between a cut-off low to the west and high pressure to the northeast. Around days 4 and 5, the cyclone should turn generally northward in response to an approaching mid-tropospheric short wave trough. An adjustment to the right of the previous forecast was made, and the NHC forecast is based on a blend of the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 21.9N 35.0W 45 KT 50 MPH 12H 05/1800Z 22.7N 35.8W 45 KT 50 MPH 24H 06/0600Z 24.2N 37.3W 45 KT 50 MPH 36H 06/1800Z 26.1N 39.1W 45 KT 50 MPH 48H 07/0600Z 28.0N 41.0W 45 KT 50 MPH 72H 08/0600Z 31.6N 46.1W 55 KT 65 MPH 96H 09/0600Z 35.8N 48.7W 60 KT 70 MPH 120H 10/0600Z 40.6N 44.7W 60 KT 70 MPH $$ Forecaster Roberts |
