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Chill falls over the Atlantic as the official season heads towards close
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| #939354 (Received by flhurricane at: 10:38 AM 10.Sep.2018) TCDAT4 Hurricane Isaac Discussion Number 12 NWS National Hurricane Center Miami FL AL092018 1100 AM AST Mon Sep 10 2018 Isaac's cloud pattern is currently a bit ragged-looking, with an irregular CDO and limited convective banding. Dvorak intensity estimates from both TAFB and SAB are 65 kt, and that value will be used for the advisory. There is significant uncertainty in the intensity forecast for this system. Vertical wind shear over the hurricane is forecast to be weak to moderate during the next day or so, which should allow Isaac to strengthen somewhat. By 48 hours, however, the global models depict significantly stronger northwesterly shear, associated with an upper-level trough over the central Atlantic, affecting the tropical cyclone. Most of the guidance does not show Isaac strengthening over the Caribbean. The HWRF model is an outlier, strengthening Isaac into a major hurricane later in the period, and it is the main contributor to high consensus forecasts at days 3-5. The NHC intensity forecast is above the model consensus through 72 hours and below it by the end of the period. Isaac continues to move westward, or 275/12 kt. A subtropical ridge should be maintained to the north of the tropical cyclone for the next several days, so a continued westward track seems likely. The U. K. Met. Office model is an outlier and shows Isaac turning northwestward and northward to the northeast of the Leeward Islands. The official track forecast, like the previous one, follows the other reliable global models and is also close to the HFIP corrected consensus guidance. Key Messages: 1. Isaac is a small hurricane and uncertainty in the forecast is greater than normal. Although Isaac is forecast to begin weakening when it approaches the Lesser Antilles, it is still expected to be at or near hurricane intensity when it reaches the islands. 2. Interests in the Lesser Antilles should continue to monitor Isaac during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 14.7N 43.9W 65 KT 75 MPH 12H 11/0000Z 14.9N 45.9W 70 KT 80 MPH 24H 11/1200Z 15.0N 48.7W 75 KT 85 MPH 36H 12/0000Z 15.0N 51.4W 75 KT 85 MPH 48H 12/1200Z 15.1N 54.0W 75 KT 85 MPH 72H 13/1200Z 15.4N 59.4W 70 KT 80 MPH 96H 14/1200Z 15.5N 64.5W 60 KT 70 MPH 120H 15/1200Z 15.7N 70.0W 50 KT 60 MPH $$ Forecaster Pasch |
