775
WTPZ42 KNHC 280235
TCDEP2

Tropical Storm Vance Discussion Number  27
NWS National Hurricane Center Miami FL       EP222026
800 PM MST Tue Oct 27 2026

The structure of Vance continues to be heavily sheared and ragged
based on the current visible satellite imagery. Some of the most
recent images have shown that a small convective burst has occurred
near the center, however it is also being blown away by the westerly
wind shear at this point. In addition to the shear, there is dry air
that is getting into the core of the storm, which is keeping the
center of Vance fully exposed. The most recent objective intensity
estimates from UW-CIMSS are in the range of 28-33 kt, while the
latest TAFB Dvorak fix is a T2.0/30 kt. Given the available data the
initial intensity has been held at 35 kt for this advisory.

Vance is moving northwestward at 310/07 kt, as the storm is being
steered by a low-level ridge centered over the south-central United
States. A gradual turn toward the north is forecast over the next
few days due to a strong mid-level trough moving across the U.S.
West Coast. As a result, Vance should move toward the Gulf of
California by Thursday. The current NHC track forecast is very
similar to the previous one, with some minor adjustments being made
based on the latest HCCA and GDMI forecast aids.

The intensity portion of the forecast has plenty of uncertainties
due to a variety of variables. The cyclone is over warm waters of
29-30 C for the next several days, but the wind shear is expected to
be around 40 kt based on the GFS and ECMWF SHIPS guidance. This
could allow for convection to develop near the center, but that
convection will then be blown away by the shear. This could also
mean that there could be brief fluctuations in intensity at times
due to the convection. The most recent GFS and ECMWF simulated
satellite guidance shows that there could be one or two more
convective bursts from Vance due to some upper-level divergence
sometime tomorrow. However, the impacts that this convection could
have on the storm are still uncertain. At this point, the cyclone is
still expected to become post-tropical around 36 h. By 60 h, it is
expected to be a post-tropical remnant low, and finally by 72 h the
circulation of Vance is forecast to dissipate. If the storm cannot
maintain organized deep convection, it is possible that Vance could
transition to a post-tropical cyclone sooner than currently
forecast.


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  28/0300Z 17.3N 108.4W   35 KT  40 MPH
 12H  28/1200Z 18.5N 108.7W   35 KT  40 MPH
 24H  29/0000Z 20.2N 108.5W   35 KT  40 MPH
 36H  29/1200Z 21.7N 108.1W   35 KT  40 MPH...POST-TROPICAL
 48H  30/0000Z 23.5N 107.7W   35 KT  40 MPH...POST-TROPICAL
 60H  30/1200Z 25.3N 107.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  31/0000Z...DISSIPATED

$$
Forecaster Katz/Beven