Tropical Cyclone Discussion
664 WTPZ42 KNHC 260237 TCDEP2 Tropical Storm Vance Discussion Number 19 NWS National Hurricane Center Miami FL EP222026 900 PM CST Sun Oct 25 2026 Vance's structure continues to degrade as seen in visible satellite imagery and the GPM and AMSR3 microwave passes, due to strong vertical wind shear and relatively dry mid-level air. Convection continues to develop to the northeast of the center, but it is mostly limited to that quadrant. The TAFB Dvorak fix was T3.5/55 kt and the objective intensity estimates from UW-CIMSS are in 37-52 kt range. Based on that data, the initial intensity has been lowered to 55 kt. Vance is currently moving toward the northwest, 305/6 kt. The tropical storm is being steered by a mid-level ridge centered over the south-central United States, along with a closed upper-level low moving across the southwestern United States. The cyclone is expected to continue to move toward the northwest to west-northwest with a decrease in forward speed as the steering currents weaken. A turn back to the north is expected by the middle of the week as an amplified mid to upper-level trough moves over the eastern Pacific. The current NHC track forecast has been adjusted a little to the west of the previous one. Future adjustments to the west are likely if the guidance trends continue. The combination of southwesterly wind shear and relatively dry mid-level air are expected to continue to gradually weaken the storm. By the middle of this week, an upper-level trough will further enhance the wind shear, resulting in additional weakening. Both the GFS and ECMWF simulated satellite imagery suggest that Vance will struggle to hold on to organized deep convection by late this week. The current intensity forecast still calls for Vance to become post-tropical at 96 h and degenerate into a remnant low by 120 h. However, the current intensity forecast is on the upper end of the guidance envelope, as most of the guidance shows the rate of weakening much faster than what is currently forecast. It is certainly possible that the cyclone could weaken faster, which will mean that it could become a remnant low sooner than what is forecasted. Key Messages: 1. Although the threat to southwest Mexico is decreasing as the forecast track shifts westward away from the coast, interests there should continue to monitor Vance's progress. 2. Periods of heavy rainfall associated with Vance will impact portions of western Mexico during much of this week. This rainfall may produce flooding and mudslides across Colima, Nayarit, and Sinaloa, along with western portions of Michoacán, Jalisco, and Durango, especially in areas along steep terrain. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 15.0N 104.7W 55 KT 65 MPH 12H 26/1200Z 15.3N 105.3W 50 KT 60 MPH 24H 27/0000Z 15.7N 106.0W 45 KT 50 MPH 36H 27/1200Z 16.5N 106.8W 40 KT 45 MPH 48H 28/0000Z 17.4N 107.3W 40 KT 45 MPH 60H 28/1200Z 18.5N 107.6W 40 KT 45 MPH 72H 29/0000Z 20.0N 107.7W 40 KT 45 MPH 96H 30/0000Z 22.0N 107.8W 35 KT 40 MPH...POST-TROPICAL 120H 31/0000Z 24.0N 107.9W 30 KT 35 MPH...POST-TROP/REMNT LOW