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| #1246390 (Received by flhurricane at: 10:54 AM 28.Sep.2025) TCDAT4 Tropical Depression Nine Discussion Number 8 NWS National Hurricane Center Miami FL AL092025 1100 AM EDT Sun Sep 28 2025 Structurally, the depression continues to gradually become better organized, with an attempt at more bursting convection closer to the estimated center. However, recent observations from the ongoing Air Force Reserve Reconnaissance aircraft mission have been rather underwhelming, which still shows a broad wind field and a peak 850-mb wind of only 37 kt. Based on this information, the system will remain a depression for this advisory with maximum sustained wind of 30 kt, which is a little under the satellite-based intensity estimates. The depression has not really accelerated much yet this morning, and it appears to be moving slowly northward at 350/6 kt. A general north-northwest to northward motion is expected to continue for the next 24-36 hours as southerly steering persists from both an upper trough over the southeastern United States and the subtropical ridge centered just east of Bermuda. After that period of time, the subtropical ridge's steering influence decreases as Hurricane Humberto's larger outer circulation creates a large weakness. Given the slow motion of the depression so far, it has also remained south of a track bifurcation point that was seen yesterday in the ensemble guidance. The tropical cyclone now appears more likely to turn sharply east-northeastward starting on Tuesday and continuing through the remainder of the forecast. The track guidance this cycle has made another south and eastward shift, and the NHC track forecast has been moved in that direction. In particular, the track guidance continues to show much more east-northeastward acceleration at the end of the forecast, requiring large speed changes in days 4 and 5, and this still might not be fast enough. The latest track forecast is very close to the HCCA consensus aid, but blends it with a little more of the Google DeepMind ensemble mean (GDMI) by the day 5 forecast. While the depression has not yet developed an inner core, one is expected to form in the next 12-24 hours. Some southerly vertical wind shear is expected to persist, though it never gets prohibitively strong, remaining under 20 kt for the next 48-72 h in the GFS-based SHIPS. Therefore, intensification is expected and the latest NHC intensity forecast is roughly in line with the intensity guidance consensus aids. In 3-4 days, the cyclone is expected to find itself in the right entrance region of an intensifying upper-level jet, and the enhanced upper-level divergence in that time may help support additional intensification even as the shear begins to increase towards the end of the forecast. After the system passes Bermuda, a strong baroclinic zone is expected to interact with the system, resulting in extratropical transition by day 5 as it gets tangled up with a frontal boundary. However, as stressed previously, this is a low confidence forecast at long range given the recent large track changes, especially since the southward shift in track keeps the cyclone over warmer sea-surface temperatures. KEY MESSAGES: 1. The depression is expected to strengthen and bring tropical storm conditions to portions of the central and northwestern Bahamas through Monday. Tropical storm conditions are also possible along portions of the east coast of central Florida beginning Monday. 2. Rainfall associated with the system will continue to impact eastern Cuba and the Bahamas through Tuesday, which will likely produce flash and urban flooding. Mudslides are possible in the higher terrain. Heavy rainfall across the coastal Carolinas could cause flash, urban, and river flooding into Wednesday morning. 3. The risk of significant wind impacts along the southeastern United States coast is decreasing, but interests in that area should continue to monitor the latest forecast updates. 4. Swells and high surf from both Humberto and Tropical Depression Nine are expected to produce dangerous marine conditions and rip currents along the east coast of Florida and the Georgia coast through Monday. These conditions are expected to spread northward along much of the east coast of the United States early this week. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 23.5N 77.3W 30 KT 35 MPH 12H 29/0000Z 24.5N 77.4W 40 KT 45 MPH 24H 29/1200Z 26.2N 77.6W 50 KT 60 MPH 36H 30/0000Z 27.7N 77.6W 60 KT 70 MPH 48H 30/1200Z 28.8N 77.1W 65 KT 75 MPH 60H 01/0000Z 29.3N 75.7W 70 KT 80 MPH 72H 01/1200Z 29.9N 73.5W 75 KT 85 MPH 96H 02/1200Z 31.0N 68.0W 80 KT 90 MPH 120H 03/1200Z 32.5N 61.5W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin |
