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| #939800 (Received by flhurricane at: 10:39 PM 12.Sep.2018) TCDAT3 Hurricane Helene Discussion Number 23 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Wed Sep 12 2018 Helene`s surface circulation has become rather difficult to find this evening in shortwave and enhanced infrared satellite imagery. Based on an earlier SSMI/S microwave pass, the center was removed well to the south of the convective mass. A blend of the Dvorak intensity estimates from TAFB and SAB, as well as a SATCON analysis of 72 kt, yields an initial intensity of 70 kt for this advisory. Global models and the ECMWF/GFS Decay SHIPS models show the southwesterly shear increasing significantly in 24 hours, however, the warm sea surface temperatures are expected to limit the weakening trend some. Beyond the 48 hour period, Helene is expected to traverse cooler waters while the harsh upper wind environment persists. Therefore, additional weakening is forecast at a faster rate. Toward the end of the period, the global models, as well as the Florida State Cyclone Phase Evolution analysis and forecast product, show Helene transitioning to a post-tropical extratropical cyclone as it moves toward Ireland and the United Kingdom. Helene is estimated to be moving northward, or 350/11 kt, within the mid-tropospheric southerly flow produced by an amplifying deep-layer trough over the central Atlantic. At the 48 hour period, the cyclone should turn to the north-northeast followed by a northeastward turn with an increase in forward motion toward the end of the forecast period. The large-scale models, and the HWRF hurricane model, are clustered fairly close together and indicate that Helene will pass near the Azores in about 72 hours. Interests in those islands should closely monitor the progress of Helene over the next several days. The NHC forecast lies in the middle of the guidance envelope and is nudged toward the TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 22.4N 36.9W 70 KT 80 MPH 12H 13/1200Z 24.4N 37.1W 60 KT 70 MPH 24H 14/0000Z 27.3N 37.0W 55 KT 65 MPH 36H 14/1200Z 30.7N 36.4W 55 KT 65 MPH 48H 15/0000Z 34.3N 35.3W 55 KT 65 MPH 72H 16/0000Z 40.1N 30.5W 50 KT 60 MPH 96H 17/0000Z 43.4N 22.4W 50 KT 60 MPH 120H 18/0000Z 48.7N 12.9W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts |
