903
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
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