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| #1246251 (Received by flhurricane at: 10:54 AM 27.Sep.2025) TCDAT4 Tropical Depression Nine Discussion Number 4 NWS National Hurricane Center Miami FL AL092025 1100 AM EDT Sat Sep 27 2025 Deep convection has increased over the disturbance this morning, and dropsonde data from a NOAA Hurricane Hunter aircraft indicate pressures are gradually falling between the central Bahamas and eastern Cuba. In addition, dropsonde and flight-level wind data from the aircraft show the low-level circulation has become better defined. Based on these developments, the disturbance is now classified as a 30-kt tropical depression for this advisory. An Air Force Reserve Hurricane Hunter mission is scheduled to investigate the disturbance later today. The initial motion of the depression is an uncertain 320/5 kt. A north-northwestward motion is expected as the system moves between a deep-layer trough over the southeastern U.S. and a subtropical ridge over the Atlantic. The track models are in good agreement through 72 h, and little change was made to this portion of the NHC track forecast. This brings the center over the central and northwestern Bahamas this weekend, moving roughly parallel to but offshore the east coast of Florida. During this time, strengthening is forecast as the system moves over warm waters within a diffluent upper-level environment. However, the aforementioned trough should impart moderate southerly shear over the cyclone, likely resulting in an asymmetric storm structure. The near-term NHC intensity forecast was raised slightly from the previous one and still shows a 65-kt hurricane early next week off the southeastern U.S coast. The track forecast beyond 72 h is still of low confidence, with a bifurcation of solutions noted in the various deterministic models and GFS, ECMWF, and Google DeepMind ensemble members. Much depends on the future track of Hurricane Humberto, the extent to which it erodes the steering ridge over the Atlantic, and the strength and timing of an upper trough expected to dig over the northwestern Atlantic next week. A majority of the deterministic guidance suggests that the system will slow down or briefly stall offshore of the southeast U.S. coast before turning sharply eastward. There remains considerable uncertainty in how quickly this might occur, and it must be noted that some ensemble solutions still show the system reaching the coast. For now, the NHC forecast continues to show an eastward turn at days 4-5, but at a much slower forward speed than most of the models. Given the risk of tropical-storm-force winds along the east coast of Florida, a Tropical Storm Watch has been issued from the Palm Beach/Martin County Line northward to the Flagler/Volusia County Line. Although it is still too early to specify the details of potential impacts along the remainder of the southeast U.S. coast, there remains a risk of heavy rainfall, storm surge, and wind impacts. KEY MESSAGES: 1. The depression is expected to strengthen and bring tropical storm conditions to portions of the central and northwestern Bahamas through Sunday night. Tropical storm conditions are also possible along portions of the east coast of central Florida beginning Monday, where a Tropical Storm Watch has been issued. 2. Rainfall associated with this system will continue to impact eastern Cuba, Hispaniola, Jamaica, and the Bahamas through the weekend, which will likely produce flash and urban flooding. Mudslides are possible in the higher terrain. 3. There is a significant threat of heavy rainfall early next week from coastal Georgia through the Carolinas and into the southern Mid-Atlantic states, which could cause flash, urban, and river flooding. 4. The depression is expected to be at or near hurricane intensity when it approaches the southeast U.S. coast early next week, where there is a risk of storm surge and wind impacts. Although it is too soon to specify the exact location and magnitude of impacts, residents should closely monitor the latest forecast updates and ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 22.0N 76.2W 30 KT 35 MPH 12H 28/0000Z 23.0N 76.7W 35 KT 40 MPH 24H 28/1200Z 24.4N 77.3W 40 KT 45 MPH 36H 29/0000Z 26.1N 77.7W 45 KT 50 MPH 48H 29/1200Z 27.9N 78.2W 55 KT 65 MPH 60H 30/0000Z 29.6N 78.6W 60 KT 70 MPH 72H 30/1200Z 30.7N 78.8W 65 KT 75 MPH 96H 01/1200Z 31.3N 77.5W 65 KT 75 MPH 120H 02/1200Z 31.5N 75.0W 60 KT 70 MPH $$ Forecaster Reinhart |
