ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Tropical Storm Irwin Discussion Number 25 NWS National Hurricane Center Miami FL EP102017 800 AM PDT Fri Jul 28 2017 Irwin's structure has not changed significantly during the past several hours, and deep convection near the center has been blossoming intermittently. Dvorak T-numbers have also been fluctuating, and the best estimate of the initial intensity is 50 kt. SHIPS model data indicate some shear over the cyclone but not strong enough to disrupt the cloud pattern. On this basis, the NHC forecast calls for only small fluctuations in intensity during the next 24 to 36 hours. Thereafter, the circulation is expected to reach cooler waters and weakening should begin. This process will continue until Irwin and Hilary merge in about 96 hours or sooner. Irwin is embedded in light steering currents, and the cyclone has barely moved during the past few hours. Little motion is anticipated today or early Saturday, but after that time, Irwin should be steered northward and northwestward by the southerly flow in the wake of Hilary. Track guidance is in good agreement that little motion will occur during the next day or so. There is a big difference in both direction and speed among models beyond 3 days with the northernmost GFS and the southernmost ECMWF marking the edges of the broad guidance envelope. However, by then, Irwin and Hilary should have already merged. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 14.8N 125.3W 50 KT 60 MPH 12H 29/0000Z 14.8N 125.3W 55 KT 65 MPH 24H 29/1200Z 15.2N 125.4W 55 KT 65 MPH 36H 30/0000Z 16.2N 125.3W 50 KT 60 MPH 48H 30/1200Z 18.0N 125.5W 45 KT 50 MPH 72H 31/1200Z 21.5N 128.0W 35 KT 40 MPH 96H 01/1200Z...Merge with Hilary $$ Forecaster Avila NNNN
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