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Tropical Storm Helene Forecast Discussion Number 27
2018-09-14 04:34:22| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Sep 13 2018 558 WTNT43 KNHC 140234 TCDAT3 Tropical Storm Helene Discussion Number 27 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Thu Sep 13 2018 Helene's cloud pattern is beginning to have the appearance of a cyclone in extratropical transition with the rain shield limited to the northwest quadrant. The Dvorak numbers have decreased, but very recent scatterometer data show winds of around 55 kt associated with Helene's circulation, and this is the intensity value used in this advisory. Most of the guidance suggests that Helene's strength should remain steady through the forecast period, perhaps due to baroclinic forcing. On this basis, the NHC forecast keeps Helene with the same intensity through the forecast period, but as a post-tropical cyclone beyond 3 days. Helene has increased its forward speed and is now moving toward the north or 010 degrees at about 18 kt. The flow ahead of a sharp mid-level trough is well established, and this pattern will continue to steer Helene toward the north and then northeast during the next few days. This is consistent with most of the track guidance which is indeed tightly clustered. The NHC forecast is not very different from the previous one, and is in between the corrected consensus HCCA and the multi-model consensus aids. Given the increase in forward speed and the expansion of the wind field, a tropical storm warning will likely be required for a portion of the Azores early Friday. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 28.6N 36.5W 55 KT 65 MPH 12H 14/1200Z 31.4N 35.9W 55 KT 65 MPH 24H 15/0000Z 34.8N 34.7W 50 KT 60 MPH 36H 15/1200Z 37.8N 32.8W 50 KT 60 MPH 48H 16/0000Z 40.0N 29.0W 50 KT 60 MPH 72H 17/0000Z 43.0N 21.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 18/0000Z 46.5N 15.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 19/0000Z 53.0N 5.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Avila
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