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| #1156095 (Received by flhurricane at: 5:03 PM 05.Oct.2023) TCDAT2 Tropical Storm Philippe Discussion Number 50 NWS National Hurricane Center Miami FL AL172023 500 PM AST Thu Oct 05 2023 Philippe`s convective structure is gradually evolving as it begins to run into an old frontal zone to its north. A band of rain is developing over the northern part of the circulation along the old front and is beginning to move over Bermuda, while other deep convection extends east and southeast of the center. The initial intensity is held at 45 kt based on this morning`s aircraft reconnaissance data. Another mission is scheduled into Philippe this evening. The current motion is a little faster toward the north, or 360/12 kt. The track forecast reasoning has not changed. Philippe should continue accelerating northward over the western Atlantic during the next 60 hours while moving between a mid-level high over the central Atlantic and a deep-layer trough off the southeastern U.S. coast. On this track, the center will approach the coasts of Nova Scotia, New Brunswick, and eastern Maine Saturday night. After that time, Philippe is expected to turn north-northwestward ahead of an approaching mid-latitude trough, and it is forecast to become absorbed by another area of low pressure over eastern Quebec late Sunday. The NHC track forecast generally lies close to the TVCA and HCCA consensus aids during the entire forecast period. Diagnoses from the SHIPS model suggest that southwesterly shear will increase to 30 kt or more over the next 12-24 hours. Because of that, no intensification is anticipated in the short term. Extratropical transition is likely to begin on Friday as Philippe moves into and tightens the thickness gradient to its north, and that process could cause the storm to strengthen a little due to baroclinic influences. This scenario is supported by the GFS and ECMWF global models, as well as LGEM, IVCN, and HCCA consensus aids. Extratropical transition is forecast to be complete by 48 hours (Saturday afternoon) as Philippe becomes fully frontal, but the intensity is unlikely to change much before the center reaches land. Weakening is forecast once Philippe moves inland, and it`s likely that the strongest winds from the system will occur on the eastern side of the circulation, primarily over parts of Atlantic Canada. Based on the forecast for Philippe to become post-tropical by Saturday, and after coordination with National Weather Service offices in New England and the Canadian Hurricane Centre, the current plan is for hazards in New England and Atlantic Canada to be handled via local non-tropical statements and not issue tropical watches or warnings. We will continually assess this plan if the forecast evolves and tropical watches or warnings become warranted. KEY MESSAGES: 1. Tropical storm conditions are expected on Bermuda beginning early Friday morning, and a Tropical Storm Warning remains in effect. Heavy rainfall is expected to affect the island today into early Friday. This could produce flash flooding. 2. Philippe is expected to move over portions of Atlantic Canada and New England as a post-tropical cyclone this weekend. Regardless of Philippe`s intensity or structure, interests in those areas should be prepared for the possibility of strong winds and heavy rainfall and monitor statements from their local weather office. The rainfall could produce isolated to scattered instances of urban and flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 27.0N 66.2W 45 KT 50 MPH 12H 06/0600Z 29.2N 65.8W 45 KT 50 MPH 24H 06/1800Z 32.5N 65.7W 45 KT 50 MPH 36H 07/0600Z 35.5N 66.1W 50 KT 60 MPH 48H 07/1800Z 39.0N 66.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 08/0600Z 43.8N 66.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 08/1800Z 48.6N 71.4W 40 KT 45 MPH...POST-TROP/INLAND 96H 09/1800Z...DISSIPATED $$ Forecaster Berg |
