Issued at 1100 AM AST Sun Sep 24 2023
000 WTNT42 KNHC 241442 TCDAT2 Tropical Storm Philippe Discussion Number 5 NWS National Hurricane Center Miami FL AL172023 1100 AM AST Sun Sep 24 2023 Philippe is a challenging tropical cyclone to analyze this morning. On one hand, the overall satellite presentation has improved since yesterday, and a 0907Z SSMIS microwave pass shows a possible mid-level eye. Yet the 1-min GOES16 imagery reveals a weak low-level swirl southwest of the main convective blob, and ASCAT-B near 12Z showed a disorganized inner core with less wind than one might expect (albeit very contaminated with rain). Overall, intensity estimates have risen since the last advisory, so the initial wind speed is set to 45 kt, similar to the TAFB/SAB values, but this should be considered fairly uncertain. Little change in intensity is forecast with the storm during the next couple of days as increasing shear is forecast to otherwise counteract a conducive environment. There are a variety of solutions after that point, with some models showing a stronger Philippe after finding a lower-shear environment, while others suggesting that the storm succumbs to the shear from an upper-level trough. There are no easy answers here with moderate shear cases in high SST/moisture conditions well known to have higher errors due to an inherent lack of predictability. The new forecast splits the difference in the model guidance, lying near the consensus and the previous forecast, and we will just have to see if a trend emerges for the eventual intensity of Philippe. The long-term motion of the storm is westward or 280/10 kt. The subtropical ridge to the north of Philippe is forecast to gradually weaken and slide eastward in a day or two, allowing the tropical storm to move more west-northwestward and northwestward by the middle of the week. Uncertainty grows after that point, with the track seemingly dependent on the intensity. A stronger system would probably turn northward, like the GFS/HWRF/HMON models, while a weaker one, like the UKMET/ECMWF solutions, would take a left turn under the low-level subtropical ridge. For now, little change was made to the long-range forecast given all of the uncertainty. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 16.2N 41.7W 45 KT 50 MPH 12H 25/0000Z 16.5N 43.3W 45 KT 50 MPH 24H 25/1200Z 16.9N 45.6W 45 KT 50 MPH 36H 26/0000Z 17.4N 47.8W 45 KT 50 MPH 48H 26/1200Z 18.0N 49.7W 45 KT 50 MPH 60H 27/0000Z 18.9N 51.0W 50 KT 60 MPH 72H 27/1200Z 20.0N 52.5W 50 KT 60 MPH 96H 28/1200Z 22.5N 54.5W 55 KT 65 MPH 120H 29/1200Z 24.0N 55.5W 55 KT 65 MPH $$ Forecaster Blake