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Tropical Storm Irwin Forecast Discussion Number 35
2017-07-31 04:34:42| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sun Jul 30 2017 000 WTPZ45 KNHC 310234 TCDEP5 Tropical Storm Irwin Discussion Number 35 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Sun Jul 30 2017 Irwin is one resilient tropical storm. Amazingly, the cloud pattern has improved during the past few hours, with deep convection forming and rotating around the center even though the cyclone is now over sea surface temperatures colder than 25 deg C. A 0002 UTC SSMIS microwave pass revealed a small ring of deep convection that was partially open on the east side, but it also suggested that the vortex is tilted a bit with height. Since Dvorak estimates from TAFB and SAB are a consensus T3.5, the initial intensity remains 55 kt. Irwin will be moving from 24-25C waters to 22-23C waters during the next 24 hours, so weakening should begin soon. In fact, it will be quite difficult for Irwin to continue producing organized deep convection in about 36 hours, and that is when the NHC forecast calls for it to degenerate into a remnant low. Based on global model fields, the remnant low is forecast to dissipate by day 4, if not sooner. No changes to the previous NHC forecast were required based on the latest intensity guidance. The forward motion continues to increase as Irwin trails behind Hilary, and the current estimate is 335/11 kt. A little more acceleration toward the north-northwest is expected during the next 12-24 hours, but Irwin should turn northwest and slow down on days 2 and 3 as it moves around the remnant circulation of Hilary. The updated NHC track forecast was nudged northeast of the previous forecast after 24 hours to be closer in line with the latest HCCA and TVCN guidance, but otherwise no significant changes were needed. FORECAST POSITIONS AND MAX WINDS INIT 31/0300Z 19.8N 126.2W 55 KT 65 MPH 12H 31/1200Z 21.5N 127.1W 50 KT 60 MPH 24H 01/0000Z 23.9N 128.2W 40 KT 45 MPH 36H 01/1200Z 26.0N 129.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 02/0000Z 27.6N 131.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 03/0000Z 28.9N 133.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 04/0000Z...DISSIPATED $$ Forecaster Berg
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