110
WTPZ42 KNHC 261434
TCDEP2
TROPICAL STORM VANCE DISCUSSION NUMBER 21
NWS NATIONAL HURRICANE CENTER MIAMI FL EP222026
900 AM CST MON OCT 26 2026
VANCE IS EXPERIENCING 15 TO 20 KT OF WEST-SOUTHWESTERLY VERTICAL
WIND SHEAR. IT APPEARS THAT THE SURFACE CENTER IS NEAR THE
WEST-SOUTHWEST EDGE OF THE MAIN CONVECTIVE AREA. THE LATEST TAFB
CURRENT INTENSITY NUMBER REMAINS 3.5/55 KT. RECENT OBJECTIVE
INTENSITY ESTIMATES FROM UW-CIMSS HAVE BEEN RUNNING IN THE 45-55 KT
RANGE. THE INITIAL INTENSITY IS HELD AT 55 KT FOR THIS ADVISORY.
VANCE'S ESTIMATED MOTION IS WEST-NORTHWESTWARD OR 295/6 KT, AIDED BY
GPMI AND AMSR-3 MICROWAVE PASSES FROM AROUND 0800 UTC. THIS SLOW
WEST-NORTHWESTWARD TRACK IS EXPECTED TO CONTINUE 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 TO THE WEST OF THE PREVIOUS
ONE, BUT NOT AS FAR WEST AS THE GOOGLE DEEPMIND ENSEMBLE MEAN. THE
OFFICIAL FORECAST IS IN GOOD AGREEMENT WITH THE LATEST HFIP
CORRECTED CONSENSUS APPROACH (HCCA).
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) OVER
THE NEXT 12 TO 24 HOURS, AND THIS SHOULD BE ENOUGH TO CAUSE 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 FORECAST IS
SLIGHTLY LOWER THAN THE PREVIOUS FORECAST, AND LIES IN THE MIDDLE OF
THE GUIDANCE ENVELOPE THROUGH 48 HOURS, NEAR THE HCCA MODEL. FROM
60 HOURS ONWARD, THE NHC INTENSITY FORECAST IS NEAR THE LOWER END OF
THE MODEL GUIDANCE SUITE, NEAR THE AVERAGE OF THE GDMI AND HCCA
MODELS. IT IS LIKELY THAT VANCE'S CONVECTION WILL BE SHEARED OFF BY
72 HOURS, AND THE NEW FORECAST HAS MOVED UP POST-TROPICAL TIMING TO
THIS PERIOD. NEARLY ALL OF THE MODELS SHOW THE CIRCULATION
DISSIPATING BY DAY 5, SO THE NHC FORECAST SHOWS DISSIPATION BY THIS
TIME, JUST BEFORE IT 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 26/1500Z 15.4N 105.7W 55 KT 65 MPH
12H 27/0000Z 15.7N 106.6W 45 KT 50 MPH
24H 27/1200Z 16.4N 107.6W 40 KT 45 MPH
36H 28/0000Z 17.6N 108.2W 40 KT 45 MPH
48H 28/1200Z 19.2N 108.4W 40 KT 45 MPH
60H 29/0000Z 20.7N 108.4W 35 KT 40 MPH
72H 29/1200Z 22.0N 108.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 30/1200Z 24.1N 108.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 31/1200Z...DISSIPATED
FORECASTER HAGEN
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