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Hurricane Helene Forecast Discussion Number 19
2018-09-12 04:33:34| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 11 2018 516 WTNT43 KNHC 120233 TCDAT3 Hurricane Helene Discussion Number 19 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Tue Sep 11 2018 Satellite imagery indicates that Helene is gradually weakening, likely due to cool SSTs of around 25.5 deg C beneath the cyclone. The eye has become a little less distinct and cloud tops associated with the inner-core convection have warmed. The initial intensity has been lowered to 85 kt, based on a blend of Final-T and CI numbers from TAFB. Continued weakening is likely for the next 36 to 48 h since Helene will remain over marginal SSTs, and the intensity guidance is in good agreement. After that time, the cyclone will reach somewhat warmer waters and will begin to interact with an upper-level trough to the northwest. While this interaction will cause an increase of shear over Helene, it could also provide some baroclinic support to help maintain Helene's intensity before it undergoes extratropical transition. Some of the dynamical models suggest that reintensification is possible through this period, while the statistical models quickly weaken the cyclone. For now the official intensity forecast continues to show little change in intensity from 72-120 h and remains close to the various intensity consensus aids, but confidence in this portion of the forecast is lower. Virtually no change has been made to the official track forecast. Helene is currently moving northwestward, and a steady turn northward, and eventually northeastward is expected as the cyclone is steered between a mid-level ridge to the east and a trough to west. All of the global models are in good agreement, with the forward speed of the cyclone being the only notable difference from model to model. Since I have no reason to depart from the consensus at this point, the NHC forecast remains very close to HCCA through day 5. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 18.0N 35.4W 85 KT 100 MPH 12H 12/1200Z 19.3N 36.3W 75 KT 85 MPH 24H 13/0000Z 21.2N 37.3W 65 KT 75 MPH 36H 13/1200Z 23.6N 37.7W 60 KT 70 MPH 48H 14/0000Z 26.6N 37.7W 55 KT 65 MPH 72H 15/0000Z 33.7N 35.9W 50 KT 60 MPH 96H 16/0000Z 40.5N 31.0W 50 KT 60 MPH 120H 17/0000Z 45.0N 23.0W 50 KT 60 MPH $$ Forecaster Zelinsky
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