Issued at 500 AM AST Tue Sep 30 2025
000 WTNT43 KNHC 300855 TCDAT3 Hurricane Humberto Discussion Number 23 NWS National Hurricane Center Miami FL AL082025 500 AM AST Tue Sep 30 2025 Humberto is a highly sheared hurricane. Strong westerly vertical wind shear has caused the cyclone to continue its weakening trend. This is well-demonstrated by a recent AMSR2 microwave image, which shows that the convection has been sheared off from the western half of Humberto's circulation. Although the low-level center is still underneath the convective area in GOES-19 imagery, it's close to the western edge of the convection. The cyclone has taken on an elongated comma shape, with deep convection extending well off to the southeast. Subjective intensity estimates range from 77-90 kt, and objective intensity estimates from UW-CIMSS range from 70-85 kt. The advisory intensity is adjusted downward to 85 kt based primarily on this data, and also taking into account ASCAT and Air Force Hurricane Hunter data from 8-9 hours ago. Humberto is moving toward the north-northwest, or 340 degrees at 15 kt, in between a subtropical ridge to its east and Tropical Storm Imelda to its west. Humberto has tracked farther west than the previous NHC track forecast. A northward turn is expected over the next few hours as the ridge shifts east and weakens. On Wednesday, a very large mid- to upper-level trough is expected to amplify over the north Atlantic, causing Humberto to turn sharply to the east-northeast and accelerate. The NHC track forecast has been adjusted well to the left of the previous forecast at the 12 and 24 hour points, and is a bit slower than the previous forecast at 36-48 hours. The new NHC forecast is very near the various consensus aids. This track takes the core of Humberto well west and then north of Bermuda. Steady weakening is expected over the next 12 h as northwesterly vertical wind shear and intrusions of dry air persist, followed by more gradual weakening over the next day or two. By late Wednesday, Humberto is expected to merge with a mid-to upper-level trough, and that should cause the system to quickly develop frontal features and complete extratropical transition. The global models agree that Humberto will then become extremely elongated along the front and will likely no longer have a closed circulation by Thursday afternoon, so the new NHC forecast has moved forward the time of dissipation. It is important to convey that Humberto is forecast to be a large and powerful cyclone until it dissipates on Thursday. The large extratropical low in combination with Imelda will cause rough marine conditions over a large portion of the western and central Atlantic. See Key Messages below for more information. KEY MESSAGES: 1. Humberto's outer rainbands could produce gusty winds and heavy rainfall over Bermuda today and Wednesday. Please follow local updates from the Bermuda Weather Service for impacts from both Humberto and Imelda. 2. Dangerous marine conditions, including high surf and life-threatening rip currents, will continue to affect beaches of the northern Caribbean, Bahamas, Bermuda, and much of the east coast of the United States through the week. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 31.6N 69.4W 85 KT 100 MPH 12H 30/1800Z 33.5N 69.4W 75 KT 85 MPH 24H 01/0600Z 35.5N 67.7W 75 KT 85 MPH 36H 01/1800Z 36.5N 63.8W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 02/0600Z 37.3N 57.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 60H 02/1800Z...DISSIPATED $$ Forecaster Hagen
