508
WTPZ42 KNHC 260838
TCDEP2
TROPICAL STORM VANCE DISCUSSION NUMBER 20
NWS NATIONAL HURRICANE CENTER MIAMI FL EP222026
300 AM CST MON OCT 26 2026
VANCE HAS NOT CHANGED SIGNIFICANTLY IN ORGANIZATION OVER THE PAST
SEVERAL HOURS. THERE ARE DISORGANIZED BURSTS OF DEEP CONVECTION
NEAR AND EAST OF THE ESTIMATED CENTER, BUT CONVECTIVE BANDING
FEATURES ARE NOT WELL DEFINED. UPPER-LEVEL OUTFLOW IS MAINLY OVER
THE NORTHERN SEMICIRCLE OF THE SYSTEM. THE ADVISORY INTENSITY IS
HELD AT 55 KT FOR NOW, WHICH IS IN AGREEMENT WITH A SUBJECTIVE
DVORAK ESTIMATE FROM TAFB AND A LITTLE HIGHER THAN MOST OF THE
OBJECTIVE ESTIMATES FROM UW-CIMSS.
ALTHOUGH THE CENTER IS DIFFICULT TO LOCATE, IT IS ESTIMATED TO BE
SITUATED NEAR THE WESTERN SIDE OF THE MAIN AREA OF CONVECTION. THE
STORM APPEARS TO STILL BE MOVING SLOWLY NORTHWESTWARD, WITH AN
INITIAL MOTION ESTIMATE OF AROUND 305/5 KT. A SLOW
WEST-NORTHWESTWARD TRACK IS LIKELY OVER THE NEXT 36 HOURS OR SO DUE
TO A WEAK MID-LEVEL RIDGE TO THE NORTH OF THE SYSTEM. IN A COUPLE
OF DAYS, A BROAD MID-LEVEL TROUGH NEAR THE BAJA CALIFORNIA PENINSULA
SHOULD INDUCE A TURN TOWARD THE NORTH, AND THE WEAKENING CYCLONE
SHOULD THEN MOVE NORTHWARD AND APPROACH MAINLAND MEXICO LATER THIS
WEEK. THE OFFICIAL TRACK FORECAST IS SHIFTED SOMEWHAT TO THE WEST
OF THE PREVIOUS ONE, BUT NOT AS FAR WEST AS MUCH OF THE MODEL
GUIDANCE. ADDITIONAL WESTWARD ADJUSTMENTS MAY BE REQUIRED IN
SUBSEQUENT ADVISORY PACKAGES.
VANCE REMAINS IN AN ENVIRONMENT OF STRONG WESTERLY VERTICAL WIND
SHEAR AND IN A SOMEWHAT DRY MID-LEVEL AIR MASS. THE SHIPS GUIDANCE
INDICATES THAT THE STRONG SHEAR SHOULD PERSIST FOR THE NEXT FEW
DAYS. THEREFORE WEAKENING IS ANTICIPATED AS IN THE PREVIOUS NHC
FORECAST. SIMULATED SATELLITE IMAGERY FROM THE ECMWF GLOBAL MODEL
OUTPUT SHOWS VANCE LOSING MOST OF ITS DEEP CONVECTION AFTER 72
HOURS. THUS, THE SYSTEM IS EXPECTED TO BECOME A POST-TROPICAL
REMNANT LOW BY LATE THIS WEEK. THE OFFICIAL FORECAST IS ON THE HIGH
SIDE OF THE INTENSITY MODEL GUIDANCE SUITE.
KEY MESSAGES:
1. ALTHOUGH THE 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.
2. 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 SINALOA AND ALONG WESTERN
PORTIONS OF JALISCO, NAYARIT AND DURANGO, ESPECIALLY IN AREAS ALONG
STEEP TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 26/0900Z 15.3N 105.1W 55 KT 65 MPH
12H 26/1800Z 15.6N 105.9W 50 KT 60 MPH
24H 27/0600Z 16.1N 106.9W 45 KT 50 MPH
36H 27/1800Z 17.2N 107.6W 40 KT 45 MPH
48H 28/0600Z 18.5N 108.0W 40 KT 45 MPH
60H 28/1800Z 19.9N 108.1W 40 KT 45 MPH
72H 29/0600Z 21.4N 108.0W 35 KT 40 MPH
96H 30/0600Z 23.2N 107.9W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 31/0600Z 24.5N 108.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
FORECASTER PASCH
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