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Tropical Storm IRMA
ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Tropical Storm Irma Discussion Number 1 NWS National Hurricane Center Miami FL AL112017 1100 AM AST Wed Aug 30 2017 Satellite images indicate that the low pressure area in the far eastern Atlantic has become much better organized since yesterday, with many curved bands around the center. ASCAT data showed peak winds of about 42 kt, and after considering the small size of the circulation and some undersampling due to the resolution of the instrument, the initial wind speed is set to 45 kt. Global models indicate that the upper-level winds are likely to be favorable for strengthening of Irma during the next several days. However, Irma will be moving over more marginal water temperatures and into drier mid-level conditions, which should temper the intensification rate. The NHC solution is a blend of the intensity consensus and the statistical-dynamical hurricane models SHIPS and LGEM. At the end of the period, the forecast could turn out to be conservative if the very conducive environment shown in most of the global models emerges. The initial motion estimate is 280/11. A ridge over the eastern Atlantic is forecast to steer Irma westward over the next few days. Thereafter, the ridge builds southwestward, which will likely cause the storm to move, somewhat unusually, toward the west-southwest. The official forecast puts more weight on the global models than the regional hurricane models, which appear to have a northward bias on this cycle. Thus, the NHC track prediction is on the southwestern side of the guidance envelope, although not as far in that direction as the ECMWF or its ensemble mean. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 16.4N 30.3W 45 KT 50 MPH 12H 31/0000Z 16.7N 31.9W 50 KT 60 MPH 24H 31/1200Z 17.3N 33.8W 55 KT 65 MPH 36H 01/0000Z 17.9N 35.7W 60 KT 70 MPH 48H 01/1200Z 18.2N 37.6W 65 KT 75 MPH 72H 02/1200Z 18.7N 41.9W 70 KT 80 MPH 96H 03/1200Z 17.7N 46.5W 75 KT 85 MPH 120H 04/1200Z 17.0N 51.0W 80 KT 90 MPH $$ Forecaster Blake NNNN