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Tropical Storm Irwin Forecast Discussion Number 23
2017-07-28 04:54:53| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Thu Jul 27 2017 000 WTPZ45 KNHC 280254 TCDEP5 Tropical Storm Irwin Discussion Number 23 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Thu Jul 27 2017 Irwin's convective pattern has changed little since the previous advisory. A long curved but fragmented band of convection wraps almost 75 percent of the way around the circulation center, yielding a consensus Dvorak intensity estimate of T3.5/55 kt from both TAFB and SAB. However, objective estimates from UW-CIMSS ADT and NHC are T2.9/43 kt and T3.0/45 kt, respectively, which are supported by an earlier UW-CIMSS AMSU estimate of 45 kt. Based on average of these estimates, the initial intensity has been held at 50 kt. The initial motion estimate is a slow drift toward the west, or 270/02 kt. For such weak steering currents, the latest NHC model guidance is in very good agreement on Irwin moving little for the next 36 hours or so, followed by a faster motion toward the north at 48 and 72 hours as the cyclone moves up the eastern and the northern sides of Tropical Storm Hilary. Irwin is then forecast to merge with Hilary by 96 hours. The new NHC track forecast is similar to the previous advisory, and lies close to the multi-model consensus TVCN. The overall environment surrounding Irwin is expected to change little before the cyclone merges with Tropical Storm Hilary, so only minor fluctuations in intensity are forecast, based primarily on slight changes in the vertical wind shear. The new forecast follows the previous advisory and the consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 14.9N 124.6W 50 KT 60 MPH 12H 28/1200Z 14.8N 124.8W 50 KT 60 MPH 24H 29/0000Z 14.8N 125.0W 55 KT 65 MPH 36H 29/1200Z 15.0N 125.1W 55 KT 65 MPH 48H 30/0000Z 16.4N 124.8W 50 KT 60 MPH 72H 31/0000Z 20.0N 126.0W 45 KT 50 MPH 96H 01/0000Z...MERGED WITH TROPICAL STORM HILARY $$ Forecaster Stewart
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