Issued at 1100 AM EDT Mon Sep 29 2025
000 WTNT44 KNHC 291459 TCDAT4 Tropical Storm Imelda Discussion Number 12 NWS National Hurricane Center Miami FL AL092025 1100 AM EDT Mon Sep 29 2025 Imelda is strengthening this morning. We have had plenty of data from both the NOAA and Air Force Reserve Hurricane Hunters, and both of their observations show that the tropical storm is becoming better organized. This matches the improving structure on satellite which shows a bursting central dense overcast. However, Tail Doppler Radar (TDR) analysis still shows some modest tilt north with height between the 1 km and 5 km centers. The peak 750 mb flight level winds from the NOAA-P3 was up to 59 kt to the northeast of the center, and the most recent dropsonde from the C-130 center fix was 990 mb with 20 kt of wind. Thus, the initial intensity for Imelda has been raised to 50 kt this advisory, with a minimum pressure of 988 mb. The northwest Bahamas continue to get tropical storm conditions, and there was a recent wind gust to 72 kt at Treasure Cay. The tropical storm continues to move northward at about 7 kt. This motion is forecast to continue today due to steering along the western side of the subtropical ridge and eastern side of a mid to upper-level trough located over the southeastern U.S. The steering from the subtropical ridge is about to become interrupted by Hurricane Humberto's large circulation as the upstream trough starts to dig in behind Imelda. The combination of these changes will cause the tropical cyclone's track to shift abruptly east-northeastward as it accelerates. The latest track guidance is fairly similar to the previous cycle, though there remains a substantial amount of along-track spread over the 36-60 h period, where the ECMWF is on the slow end of the guidance envelope, and the GFS and Google DeepMind ensemble mean (GDMI) are on the faster end. The latest NHC track forecast is along the prior forecast track, but a little faster after 36 h, blending the HCCA and GDMI track guidance. On the current forecast track, the center of Imelda is forecast to pass near Bermuda in about 60-h, though the exact timing of this remains low confidence. Evidence from both the aircraft and satellite observations show that Imelda is beginning to develop an inner core, and further intensification is expected in a low to moderate vertical wind shear environment along with sufficient mid-level moisture and plenty warm sea-surface temperatures. In 48-60 h, the shear begins to increase dramatically and the storm could pass near the cold wake of Humberto. However, Imelda is also likely to get a intensity boost from a favorable trough interaction, which could enhance the winds along the cyclone's northwestern flank, and a higher 85 kt peak is now shown during this time. This enhancement could evolve into a "sting jet" like feature as the system becomes extratropical. The timing of this transition remains difficult to determine, since the ECMWF forecast is much slower and further south, keeping the cyclone over warmer SSTs. My best guess is that this process will be complete between the 72 to 96 h forecast points. The official forecast remains at the higher end of the model guidance, but is pretty close to the HCCA consensus aid. KEY MESSAGES: 1. Imelda is expected to continue to bring tropical storm conditions to portions of the northwestern Bahamas today. 2. Rainfall associated with Tropical Storm Imelda will continue to impact the Bahamas through Tuesday, which will likely produce flash and urban flooding. Heavy rainfall across the coastal Carolinas could cause isolated flash and urban flooding through Tuesday. 3. Interests in Bermuda should monitor the progress of Imelda as a Hurricane Watch could be required this afternoon. 4. Swells and high surf from both Humberto and Imelda are expected to produce dangerous marine conditions and rip currents along much of the East Coast of the United States during the next several days. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 26.9N 77.1W 50 KT 60 MPH 12H 30/0000Z 28.0N 77.0W 60 KT 70 MPH 24H 30/1200Z 29.0N 75.9W 70 KT 80 MPH 36H 01/0000Z 29.7N 73.6W 75 KT 85 MPH 48H 01/1200Z 30.8N 70.2W 80 KT 90 MPH 60H 02/0000Z 32.3N 65.4W 85 KT 100 MPH 72H 02/1200Z 33.7N 60.0W 80 KT 90 MPH 96H 03/1200Z 38.0N 53.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 04/1200Z 43.0N 49.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin
