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Tropical Storm Philippe Forecast Discussion Number 6
2017-10-29 03:41:32| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat Oct 28 2017 000 WTNT43 KNHC 290241 TCDAT3 Tropical Storm Philippe Discussion Number 6 NWS National Hurricane Center Miami FL AL182017 1100 PM EDT Sat Oct 28 2017 Philippe has a very non-classical structure for a tropical cyclone this evening. A combination of satellite imagery, radar data, and surface observations show that the circulation center is elongated northwest-southeast from southwest of Naples, Florida, to central Cuba with at least three vorticity centers present in this area. The estimated center position is a mean of the multiple vorticity centers, with this position near the region of lowest pressure suggested by the surface observations. Currently, the primary deep convection is located from the northwestern Bahamas southwestward across Cuba into the Caribbean, with a smaller area of convection over the southeastern Gulf of Mexico. The initial intensity remains 35 kt, based mainly on continuity from the previous advisory. The initial motion is a rather uncertain 015/21. A deep-layer trough and developing surface low over the eastern United States should cause Philippe to turn northeastward soon, followed by a rapid northeastward motion across the southern end of the Florida Peninsula into the Atlantic. The cyclone should continue to move around the large baroclinic system until it is absorbed after the 48 h point. The new forecast track is a blend of the previous forecast and the current guidance, and it is shifted to the north of the previous track based mainly on the current initial position. It is unclear how much additional strengthening Philippe can do as a tropical cyclone, as the shear is increasing over the system and water vapor imagery shows dry air entrainment in the southwestern quadrant. However, the upper-level divergence over the system is very strong, and the large-scale models forecast deepening as the center crosses southern Florida and the Bahamas. In addition, the increasing forward speed may increase the maximum winds as well. Based on these factors, the intensity forecast calls for some increase in strength during the next 24-36 h. Philippe is likely to merge with a frontal system associated with the eastern U. S. trough in about 36 h, and the mid-latitude cyclone should completely absorb Philippe after 48 h, if not sooner. KEY MESSAGES: 1. Although the center of Philippe is now forecast to move across the Florida Keys or extreme south Florida, most of the strongest winds are expected to remain well east and southeast of the center. However, tropical-storm-force winds, mainly in gusts, could occur in brief heavy squalls across the upper Florida Keys and southeast Florida overnight. For that reason, a tropical storm watch remains in effect for these areas. 2. Regardless of the exact track of Philippe, the primary threat from this system will be heavy rainfall that can cause localized flooding across portions of Cuba, the Florida Keys, and South Florida. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 24.8N 82.1W 35 KT 40 MPH 12H 29/1200Z 27.6N 78.9W 40 KT 45 MPH 24H 30/0000Z 33.9N 74.0W 50 KT 60 MPH 36H 30/1200Z 40.3N 69.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 31/0000Z 48.0N 67.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 01/0000Z...ABSORBED BY EXTRATROPICAL LOW $$ Forecaster Beven
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