Tropical Cyclone Discussion
195 WTPZ42 KNHC 280833 TCDEP2 Tropical Storm Vance Discussion Number 28 NWS National Hurricane Center Miami FL EP222026 200 AM MST Wed Oct 28 2026 Vance's low-level circulation remains partially exposed due to strong westerly vertical wind shear affecting the cyclone. However, satellite imagery indicates that deep convection has expanded near the center and across the eastern semicircle of the circulation early this morning, with cloud-top temperatures as cold as -85 C. This increase in convection could be partly associated with the nocturnal convective maximum, despite the persistent strong westerly shear. A 0411 UTC Metop-C scatterometer pass indicated that Vance's low-level circulation was not as well defined and had become elongated from east to west, with peak winds of 30 to 35 kt east of the center. Given these observations and the recent convective presentation, the initial intensity is held at 35 kt. The initial motion is northward, or 360/10 kt. A gradual turn toward the north-northeast is expected today as the low- to mid-level ridge to the northeast of Vance erodes in response to a series of shortwave troughs rotating through a broad mid- to upper-level trough deepening over the West Coast of the United States. The track guidance remains in good agreement with this scenario, bringing Vance west of the Islas Marias tonight or early Thursday, followed by a forecast landfall along the coast of Mexico north of Mazatlan on Thursday. The latest NHC track forecast is essentially unchanged from the previous prediction and lies near the GDMI and HCCA aids. Strong westerly to southwesterly vertical wind shear associated with the subtropical jet is expected to increase further as Vance moves northward toward the deepening upper-level trough. This shear, combined with dry mid-level air, should continue to inhibit sustained organization of deep convection near the center despite warm sea surface temperatures along the forecast track. Global model guidance generally supports this scenario, depicting intermittent convective bursts primarily displaced east of the circulation. However, some intensity guidance suggests that Vance could maintain its strength or even strengthen slightly during the next day or so, possibly due to enhanced upper-level divergence associated with the interaction between the subtropical jet and upper trough. Given this possibility, the NHC forecast maintains Vance's intensity at 35 kt through 24 h, followed by gradual weakening thereafter. The increasingly elongated and less well-defined low-level circulation suggests that Vance could degenerate into a post-tropical remnant low sooner than previously forecast, and the latest forecast indicates this transition by 36 h. Given the forecast weakening and expected loss of tropical characteristics, the threat of tropical storm conditions over land remains low at this time. The latest NHC intensity forecast is very similar to the previous prediction and lies near the middle of the guidance envelope. Key Messages: 1. 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 central and southern Sinaloa, western Durango, and northwestern Nayarit, especially in areas along steep terrain. 2. Interests along the southwestern and west-central coasts of Mexico and the southern Baja California Peninsula should monitor the progress of Vance. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 18.6N 108.6W 35 KT 40 MPH 12H 28/1800Z 20.0N 108.7W 35 KT 40 MPH 24H 29/0600Z 21.6N 108.3W 35 KT 40 MPH 36H 29/1800Z 23.1N 108.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 30/0600Z 25.2N 107.1W 25 KT 30 MPH...POST-TROP/INLAND 60H 30/1800Z...DISSIPATED