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Hurricane Helene Forecast Discussion Number 20
2018-09-12 10:35:06| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Sep 12 2018 538 WTNT43 KNHC 120835 TCDAT3 Hurricane Helene Discussion Number 20 NWS National Hurricane Center Miami FL AL082018 500 AM AST Wed Sep 12 2018 Earlier this morning, Helene looked quite ragged in IR imagery. The eye became poorly defined and cloud tops were steadily warming. However, beginning around 0500 UTC, a new burst of convection began wrapping around the previously open western portion of Helene's inner core. Objective and subjective Dvorak current intensity estimates range from 77 to 91 kt, and the initial intensity is therefore set at 80 kt as a blend of all of these data. Despite the fact that Helene appears to be on the upswing at the moment, the cyclone is still passing over sub-26 deg C waters and all of the intensity guidance shows weakening for the next 24 h. Beyond that time, there is still some spread among the intensity models, though it has decreased since the last advisory. Helene will begin interacting with a mid-latitude trough over the north-central Atlantic, which will result in an increase in shear over the hurricane. However, Helene will also begin to move over warmer waters and could get some baroclinic support from the upper-level trough. Overall the intensity guidance is a little lower than before, and now the NHC intensity forecast is near the middle of the intensity guidance envelope. Once again, no meaningful change has been made to the NHC track forecast which continues to closely follow the HFIP Corrected Consensus. Helene is moving north-northwestward, and should gradually turn northward, and eventually northeastward, as the cyclone is steered between a mid-level ridge to the east and the aforementioned mid-latitude trough to northwest. The global models remain in fairly good agreement on the track of Helene, especially through 72-96 h, when Helene is forecast to pass near the Azores, and interests in those islands should closely monitor the progress of Helene over the next several days. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 19.2N 35.7W 80 KT 90 MPH 12H 12/1800Z 20.7N 36.6W 75 KT 85 MPH 24H 13/0600Z 22.9N 37.2W 65 KT 75 MPH 36H 13/1800Z 25.5N 37.3W 55 KT 65 MPH 48H 14/0600Z 28.9N 36.9W 55 KT 65 MPH 72H 15/0600Z 36.0N 34.3W 50 KT 60 MPH 96H 16/0600Z 41.0N 28.5W 50 KT 60 MPH 120H 17/0600Z 45.5N 19.0W 50 KT 60 MPH $$ Forecaster Zelinsky
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