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| #1151003 (Received by flhurricane at: 10:56 AM 02.Sep.2023) TCDAT5 Post-Tropical Cyclone Idalia Discussion Number 28 NWS National Hurricane Center Miami FL AL102023 1100 AM AST Sat Sep 02 2023 Although the center of Idalia has moved to the southeast of Bermuda, the island is experiencing the cyclone`s strongest winds, which are located on the northwestern side of the frontal boundary. Deep convection persists to the northeast of the center, but the system is still extratropical due to the presence of attached fronts. The initial wind speed remains 50 kt based on continuity. Idalia`s initial motion is eastward, or 100/8 kt, and a relatively slow eastward motion is expected to continue today. A shortwave trough is forecast to move off the coast of New England and cut off from the mid-latitude flow, which should cause Idalia to accelerate toward the northeast and then north during the next few days. Another slow down is likely on days 4 and 5 a couple of hundred miles southeast of Nova Scotia when Idalia becomes collocated with the cut-off low. The NHC track forecast is a bit east of the previous forecast, but not as far east as the HCCA aid. Even though Idalia is producing what could be considered organized deep convection, global models fields are fairly unanimous that the cyclone will not shed its associated frontal boundaries. Since the most likely scenario is that Idalia will remain an extratropical cyclone, a transition to a tropical or subtropical cyclone is no longer indicated in the official forecast during the short term (although it still can`t be completely ruled out). Little change in strength is anticipated during the next day or two, but gradual weakening is forecast toward the end of the forecast period when Idalia goes through another occlusion and fills south of Nova Scotia. Even though Idalia is no longer explicitly forecast to transition to a tropical or subtropical cyclone, NHC advisories will continue until tropical storm conditions diminish on Bermuda and the Tropical Storm Warning is discontinued (most likely some time Sunday morning). KEY MESSAGES: 1. Tropical storm conditions will continue in Bermuda through early Sunday. 2. Swells from Idalia are forecast to cause life-threatening surf and rip current conditions along portions of the east coast of the United States through Labor Day weekend. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 31.6N 63.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 12H 03/0000Z 31.7N 62.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 03/1200Z 32.9N 60.6W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 04/0000Z 34.7N 58.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 04/1200Z 36.8N 57.4W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 05/0000Z 39.0N 56.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 05/1200Z 40.8N 57.4W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 06/1200Z 42.3N 58.7W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 07/1200Z 44.3N 58.6W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg |
