Tropical Storm Vance

000
WTPZ42 KNHC 262034
TCDEP2
 
Tropical Storm Vance Discussion Number  22
NWS National Hurricane Center Miami FL       EP222026
200 PM MST Mon Oct 26 2026
 
The structure of Vance hasn't changed much since the previous 
advisory.  Visible satellite imagery is consistent with recent 
microwave fixes that the center is near the western edge of the main 
convective area.  The initial intensity will again be held at 55 kt, 
which is supported by the latest TAFB current intensity estimate and 
recent DMINT intensity estimates.

Vance has been jogging toward the west today, with the current 
motion estimated at 280/5 kt.  A slow west-northwestward track is 
expected over the next 24 hours or so due to a weak mid-level ridge 
to the north of the system.  By Wednesday, a broad mid-level trough 
near the Baja California peninsula should induce a turn toward the 
north.  The NHC track forecast has again been shifted slightly to 
the west of the previous one, and is in between the latest GDMI and 
HCCA forecasts.  It should be noted that there is considerable 
spread/uncertainty in the timing/forward speed of Vance after it 
makes the northward turn, with the HAFS and ECMWF faster to the 
north, while the GFS and GDMI show a slower northward motion.  The 
NHC forecast is a little on the slower side compared to some of the 
guidance but is faster than the GDMI.
 
Although Vance remains in a favorable thermodynamic environment with 
warm water and enough atmospheric moisture, the cyclone is 
experiencing moderate to strong west-southwesterly wind shear.  The 
wind shear is forecast to increase a bit more (to near 25 kt) by 
hour 12, and this should be enough to cause gradual to steady 
weakening over the next day or so.  On Wednesday, as Vance turns 
northward and gets closer to the broad trough over Baja California 
and the subtropical jet, the west-southwesterly vertical wind shear 
increases to over 35 kt, and is forecast to increase further on 
Thursday.  Surprisingly, most of the models hold onto this system as 
a tropical storm for a couple more days.  The NHC intensity forecast 
is similar to the previous one, and lies in the middle to lower 
portion of the guidance envelope.  It is likely that Vance's 
convection will be sheared off by 72 hours, and the NHC forecast 
shows Vance degenerating to a post-tropical remnant low around that 
time.  All of the models show the low-level circulation of Vance 
dissipating before day 4, so the timing of dissipation has been 
moved up to day 4 in the official forecast, which is before the 
circulation reaches the coast of Mexico.

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 southern Sinaloa,
southwest Durango and coastal sections of Nayarit, Jalisco, Colima
and Michoacan, especially in areas along steep terrain.
 
2. Although the wind 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.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 15.4N 106.1W   55 KT  65 MPH
 12H  27/0600Z 15.6N 106.9W   50 KT  60 MPH
 24H  27/1800Z 16.7N 107.9W   45 KT  50 MPH
 36H  28/0600Z 18.1N 108.4W   40 KT  45 MPH
 48H  28/1800Z 19.8N 108.6W   40 KT  45 MPH
 60H  29/0600Z 21.3N 108.4W   35 KT  40 MPH
 72H  29/1800Z 22.6N 108.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  30/1800Z...DISSIPATED
 
$$
Forecaster Hagen