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ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM Hurricane Helene Discussion Number 24 NWS National Hurricane Center Miami FL AL082018 500 AM AST Thu Sep 13 2018 Helene's surface circulation has become fully exposed this morning with the center decoupled about 110 miles south of edge of the remaining deep convection. Subjective and objective satellite intensity estimates have decreased and support lowering the initial intensity to 65 kt. Statistical and global model guidance show the southwesterly shear increasing significantly in 12 hours or so, however, the 26 to 27C sea surface temperatures should govern the weakening trend a little. In 3 days, Helene is forecast to move over much cooler waters while the cyclone becomes embedded in the hostile mid-latitude upper-level westerlies. Subsequently, further weakening is expected at a faster pace. By day 4, the large-scale models all show Helene acquiring extratropical cyclone characteristics as it moves toward Ireland and the United Kingdom. The NHC intensity forecast is similar to the previous advisory, and is based primarily on the NOAA-HCCA and the IVCN consensus models. Helene is still moving northward, or 355/12 kt, within the deep-layer southerly flow produced by an amplifying mid-Atlantic trough to the west of the cyclone. In 48 hours, Helene is forecast to turn north-northeastward followed by a turn toward the northeast with an increase in forward motion at the 72 hour period. The guidance suite remains tightly clustered through day 4, with some slight spread at day 5, and indicates that Helene will pass near the Azores in about 3 days. Interests in those islands should closely monitor the progress of Helene over the next few days. The official forecast is basically an update of the previous one, and lies close to the TVCN multi-model consensus through the entire forecast period. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 23.5N 37.3W 65 KT 75 MPH 12H 13/1800Z 25.7N 37.4W 60 KT 70 MPH 24H 14/0600Z 29.1N 36.9W 55 KT 65 MPH 36H 14/1800Z 32.5N 36.2W 55 KT 65 MPH 48H 15/0600Z 35.8N 34.7W 55 KT 65 MPH 72H 16/0600Z 40.7N 28.2W 50 KT 60 MPH 96H 17/0600Z 44.6N 19.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0600Z 51.1N 10.8W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts NNNN