ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM Tropical Storm Irwin Discussion Number 26 NWS National Hurricane Center Miami FL EP102017 200 PM PDT Fri Jul 28 2017 Although Irwin's structure on visible satellite images looks well organized, infrared data show that the convection is not very deep, and the cyclone lacks an inner core. Dvorak T-numbers have not changed much and still support an initial intensity of 50 kt. Some moderate shear will be affecting the cyclone during the next 24 to 36 hours, but it is not expected to be strong enough to disrupt the cloud pattern and result in weakening. On this basis, the NHC forecast calls for only small fluctuations in intensity during that period. Thereafter, the circulation is expected to reach cooler waters, and weakening should then begin. This process will continue until Irwin and Hilary merge in about 96 hours or sooner. Irwin continues to be embedded in light steering currents, and the cyclone has barely moved today. Little motion is anticipated during the next 12 hours, but by Saturday, Irwin should be steered northward and northwestward by the southerly flow in the wake of Hilary. Track guidance is in good agreement for the next 3 days, but beyond that time, models become uncertain in how the interaction of Hilary and Irwin will take place. The NHC forecast continues to call for the merging of the two weakening cyclones. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 14.9N 125.0W 50 KT 60 MPH 12H 29/0600Z 15.0N 125.0W 55 KT 65 MPH 24H 29/1800Z 15.8N 125.0W 55 KT 65 MPH 36H 30/0600Z 16.8N 125.3W 50 KT 60 MPH 48H 30/1800Z 18.7N 126.0W 40 KT 45 MPH 72H 31/1800Z 22.5N 128.0W 35 KT 40 MPH 96H 01/1800Z...DISSIPATED $$ Forecaster Avila NNNN
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