Tropical Storm Vance

000
WTPZ42 KNHC 280846
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
 
$$
Forecaster Gibbs