Issued at 500 PM AST Mon Oct 02 2023
000 WTNT42 KNHC 022056 TCDAT2 Tropical Storm Philippe Discussion Number 38 NWS National Hurricane Center Miami FL AL172023 500 PM AST Mon Oct 02 2023 The center of Philippe remains exposed this afternoon with some convection firing closer to the center over the last few hours. Heavy rainfall and thunderstorms remain displaced to the south and southeast of the center as high northwesterly vertical wind shear persists. The initial intensity is again held steady at 45 kt for this advisory, consistent with SFMR data from the Air Force Reserve reconnaissance aircraft mission showing a large area of 40-45 surface winds mostly on the east and southeast side of the system earlier this afternoon. Another Air Force Reserve mission is scheduled for this evening. The storm continues to move to the northwest (305 degrees) at 6 kt this afternoon. Philippe refuses to gain much vertical depth as a tropical cyclone and has been steered more by the lower-level ridge. Thus, the track forecast is again adjusted westward to match recent satellite trends and in line with the weaker model guidance. The cyclone is forecast to pass near Barbuda tonight before turning north-northwest north of the Leeward Islands. Around mid-week, Philippe should turn northward due to flow between a mid-level trough in the southwest Atlantic and the subtropical ridge. Uncertainty greatly increases after that point, with huge differences showing up between the GFS- and ECMWF-based guidance. The differences in model track forecasts are related to whether this trough captures Philippe's circulation, causing Philippe to move more to the north-northwest, or whether it is shunted more to the northeast ahead of the trough. Consistent with model guidance, the track forecast has shifted farther west from the previous advisory and is in line with the consensus aids and mean ensemble track guidance. Further adjustments to the west may be necessary. Strong northwesterly vertical wind shear is expected to prevent significant strengthening in the short term. Shear is forecast to decrease a bit for a short period of time in the next 2 to 3 days and could allow for some strengthening. However, almost all of the guidance is showing a less conducive environment, and the NHC forecast reflects this trend, lying on the high end of model guidance but in line with HCCA. The uncertainty is extremely large at the end of the forecast period as some models are now showing an extratropical transition due to the mid-latitude trough, but a lot depends on how strong Philippe eventually becomes, which has clearly not been very predictable during this storm's lifetime. KEY MESSAGES: 1. Tropical storm conditions are expected across Barbuda and Antigua beginning this evening while Philippe passes near and north of the area. Interests elsewhere in the northern Leeward Islands should continue to monitor this system. 2. Heavy rainfall from Philippe could produce isolated to scattered flash flooding over the northern Leeward Islands, particularly across Barbuda and Antigua, through Tuesday. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 17.6N 61.5W 45 KT 50 MPH 12H 03/0600Z 18.2N 62.2W 45 KT 50 MPH 24H 03/1800Z 19.1N 62.6W 45 KT 50 MPH 36H 04/0600Z 20.6N 63.0W 45 KT 50 MPH 48H 04/1800Z 22.2N 63.4W 45 KT 50 MPH 60H 05/0600Z 23.9N 63.8W 50 KT 60 MPH 72H 05/1800Z 26.0N 63.8W 55 KT 65 MPH 96H 06/1800Z 30.6N 62.2W 60 KT 70 MPH 120H 07/1800Z 35.0N 60.0W 65 KT 75 MPH $$ Forecaster Blake/Stevenson