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| #1156163 (Received by flhurricane at: 5:14 AM 06.Oct.2023) TCDAT2 Tropical Storm Philippe Discussion Number 52 NWS National Hurricane Center Miami FL AL172023 500 AM AST Fri Oct 06 2023 Philippe`s structure this morning is consistent of a cyclone in the initial stages of extratropical transition. While the low-level circulation center appears better defined than yesterday at this time, most of the deep convection remains displaced well east of the center, a result likely caused by nearly 30 kt of SSW vertical wind shear. There is another cloud band of linear convection to the northwest of the center, but this appears more related to synoptic forcing caused by an upper-level cutoff low triggering non-tropical surface cyclogenesis west of Philippe. The interaction of this low with Philippe will likely dictate how quickly its completion of extratropical transition is. The initial intensity this advisory remains at 45 kt, which remains on the high end of the satellite estimates. Philippe appears to be taking a jog to the north-northeast this morning with some acceleration, estimated at 15/16 kt. The storm is caught in the flow between the aforementioned cutoff low to its west, and a amplified mid-level ridge to its east. An additional complication is the non-tropical surface cyclone forming to the west of Philippe that may also interact with it over the next day or so. The end result of this interaction is that there might be a short-term north-northeastward deviation in Philippe`s motion, but then pivots back north-northwest as the two systems undergo some binary interaction with each other. The track guidance this cycle shows this short-term deviation, but end up roughly along the previous forecast track after 24 hours. The NHC track forecast is thus only shifted some early on, showing a bit more of short-term eastward bend before Philippe resumes a northward and then north-northwestward track, close to the simple and corrected consensus aids. While environmental conditions are becoming increasingly hostile for intensification as a tropical cyclone, Philippe`s winds may still increase slightly over the next 24-36 h as it gets some baroclinic enhancement from the aforementioned upper-level trough interaction with the system. This trough interaction is also likely responsible for initiating its extratropical transition, and the latest forecast now shows Philippe completing this process and becoming a post-tropical cyclone in 36 h. Given the current structure, this could occur sooner after passing by north of Bermuda. Another even more amplified trough should fully capture this post-tropical cyclone, and weakening is expected after Philippe moves inland over New England and Atlantic Canada on Sunday. Whats left of Philippe will be absorbed by a much larger mid-latitude cyclone that is expected to occlude over Quebec. The official NHC intensity continues to lie near the middle of the guidance envelope. Based on the forecast for Philippe to become post-tropical on 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 beginning on Bermuda and expected to continue today, where a Tropical Storm Warning remains in effect. Heavy rainfall is expected to affect the island 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 may produce isolated to scattered instances of urban and flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 29.5N 65.3W 45 KT 50 MPH 12H 06/1800Z 31.9N 64.9W 45 KT 50 MPH 24H 07/0600Z 35.0N 65.6W 50 KT 60 MPH 36H 07/1800Z 38.1N 66.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 08/0600Z 42.3N 67.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 08/1800Z 48.1N 71.6W 35 KT 40 MPH...POST-TROP/INLAND 72H 09/0600Z...ABSORBED BY LARGER EXTRATROPICAL CYCLONE $$ Forecaster Papin |
