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Post-Tropical Cyclone Isaias Forecast Discussion Number 32
2020-08-05 04:46:49| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Tue Aug 04 2020 000 WTNT44 KNHC 050246 TCDAT4 Post-Tropical Cyclone Isaias Discussion Number 32 NWS National Hurricane Center Miami FL AL092020 1100 PM EDT Tue Aug 04 2020 Satellite and radar data, along with surface observations, indicate that Isaias has lost its tropical cyclone characteristics as it merges with a weak baroclinic zone over New England and southeastern Canada. Thus, it is being designated a post-tropical cyclone. The initial intensity is reduced to 40 kt based mainly on a recent observation at the Isle of Shoals, New Hampshire, and these winds are occurring over the Gulf of Maine well to the southeast of the center. The post-tropical cyclone is expected to weaken further, with winds dropping below 35 kt early tomorrow. After that, the system is forecast to be absorbed into a large baroclinic low over southeastern Canada between 36-48 h. The initial motion remains north-northeastward or 020/33 kt. A continued general north-northeastward motion with a decrease in forward speed is expected until the cyclone is absorbed by the larger low. The new NHC track forecast is similar to the previous forecast and is in the center of the tightly-clustered track guidance models. While Isaias is now post-tropical, the National Hurricane Center will continue to issue advisories until the Tropical Storm Warning can be discontinued along the coast of the United States. Key Messages: 1. Tropical storm force winds that could cause tree damage and power outages will continue over portions of New England for a few more hours. 2. As the rainfall exits the United States, scattered minor to moderate and isolated major river flooding is ongoing or forecast across portions of the Mid-Atlantic with most rivers falling below flood stage Wednesday. Quick-responding rivers in the Northeast will also be susceptible to minor and possible moderate river flooding. 3. The threat of tornadoes will continue over portions of Maine for a few more hours. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 45.3N 72.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 12H 05/1200Z 49.1N 71.1W 30 KT 35 MPH...POST-TROP/EXTRATROP 24H 06/0000Z 52.6N 70.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 36H 06/1200Z 54.0N 68.2W 25 KT 30 MPH...POST-TROP/EXTRATROP 48H 07/0000Z...DISSIPATED $$ Forecaster Beven
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