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Tropical Storm Irwin Forecast Discussion Number 31
2017-07-30 04:32:34| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sat Jul 29 2017 000 WTPZ45 KNHC 300232 TCDEP5 Tropical Storm Irwin Discussion Number 31 NWS National Hurricane Center Miami FL EP102017 800 PM PDT Sat Jul 29 2017 Irwin had a partially cloud-free region near its center in visible satellite imagery a few hours ago, but that feature has since filled, and cloud-top temperatures have cooled in the central region. Satellite intensity estimates range widely from 35 kt to 55 kt, but an ASCAT pass from around 1800 UTC showed maximum winds just over 40 kt in the southeastern quadrant. Based on that data, the initial intensity is lowered to 45 kt. Although the shear over the cyclone is low and should remain low for several days, Irwin only has another 12 hours or so before it reaches waters colder than 26 deg C. Therefore, additional weakening is anticipated after 12 hours, and Irwin could degenerate into a remnant low as early as 48 hours while it is over sea surface temperatures of 22 deg C. Based on a consensus of the global models, the remnant low should dissipate by day 5. Irwin is accelerating toward the north as anticipated, and the initial motion is now 355/7 kt. The cyclone should turn north-northwestward soon and continue accelerating during the next 36 hours in the wake of Tropical Storm Hilary. After 48 hours, once the two remnant circulations get even closer together, Irwin is likely to turn northwestward and slow down considerably. There is a normal amount of spread among the track guidance, and the updated NHC track forecast was only shifted slightly northeast of the previous forecast on days 3 and 4 to lean closer to the ECMWF, HCCA, and the various multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 16.4N 124.6W 45 KT 50 MPH 12H 30/1200Z 17.7N 125.0W 45 KT 50 MPH 24H 31/0000Z 19.9N 126.0W 40 KT 45 MPH 36H 31/1200Z 22.3N 127.4W 35 KT 40 MPH 48H 01/0000Z 24.6N 128.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0000Z 27.4N 132.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 03/0000Z 28.5N 133.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 04/0000Z...DISSIPATED $$ Forecaster Berg
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