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| #1150914 (Received by flhurricane at: 10:50 PM 01.Sep.2023) TCDAT5 Post-Tropical Cyclone Idalia Discussion Number 26 NWS National Hurricane Center Miami FL AL102023 1100 PM AST Fri Sep 01 2023 Satellite images and surface observations indicate that Idalia remains an extratropical cyclone with frontal features extending through the center. However, deep convection has recently formed just to the northeast of the center, and that could signal the beginning of a transition to a subtropical or tropical cyclone. The initial intensity is held at 45 kt. The cyclone is still moving eastward, or 100 degrees, at about 14 kt. A continued eastward motion, but at a much slower pace, is expected on Saturday as the system separates from a deep-layer trough. After that time, a turn to the northeast and then the north is forecast as the cyclone cuts off from the progressive flow over the north Atlantic. The NHC track forecast is a little slower than the previous one to be in better agreement with the latest consensus models. GFS and ECMWF simulated satellite images suggest that deep convection will continue to increase near the center overnight, and that could influence Idalia`s transition to a tropical or subtropical cyclone on Saturday. There could also be some increase in strength during that time. However, by late in the weekend, very strong southwesterly shear is expected to affect the system and that should end the opportunity for strengthening and cause the system to transition back to an extratropical cyclone. The NHC intensity forecast is similar to the previous one and near the middle of the guidance envelope. KEY MESSAGES: 1. Tropical storm conditions are expected in Bermuda on Saturday. Heavy rainfall will likely cause areas of flash and urban flooding on the island through the weekend. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 31.8N 65.3W 45 KT 50 MPH...POST-TROPICAL 12H 02/1200Z 31.6N 64.3W 50 KT 60 MPH...TROPICAL CYCLONE 24H 03/0000Z 31.8N 62.9W 50 KT 60 MPH 36H 03/1200Z 32.8N 61.2W 50 KT 60 MPH 48H 04/0000Z 34.5N 59.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 04/1200Z 36.7N 58.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 05/0000Z 38.8N 58.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 06/0000Z 41.1N 58.8W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 07/0000Z 42.6N 58.9W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi |
