911
WTPZ42 KNHC 252035
TCDEP2
TROPICAL STORM VANCE DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL EP222026
300 PM CST SUN OCT 25 2026
VERTICAL WIND SHEAR AND RELATIVELY DRY MID-LEVEL AIR ARE NEGATIVELY
IMPACTING VANCE'S STRUCTURE TODAY. AN EARLIER RCM-2 MICROWAVE PASS
INDICATED THAT THE CENTER WAS SLIGHTLY ELONGATED, WITH AN OPENING
ON THE SOUTHEASTERN SIDE. DEEP CONVECTION HAS BEEN INTERMITTENT OVER
THE PAST 6 H OR SO, AND HAS BEEN CONCENTRATED PRIMARILY NORTH AND
EAST OF THE CENTER. HOWEVER, AN ASCAT-C PASS INDICATED PEAK WINDS
OF 50-53 KT TO THE WEST AND NORTHWEST OF THE CENTER. SUBJECTIVE AND
OBJECTIVE INTENSITY ESTIMATES HAVE CONTINUED TO TREND DOWNWARD,
RANGING FROM 46-65 KT. THE INITIAL INTENSITY IS SET AT 60 KT FOR
THIS ADVISORY, BASED ON A BLEND OF THESE ESTIMATES AND THE AVAILABLE
SATELLITE DATA.
VANCE IS MOVING AT 330/06 KT, STEERED BY A MID-LEVEL RIDGE CENTERED
OVER THE SOUTH-CENTRAL UNITED STATES, ALONG WITH A CLOSED
UPPER-LEVEL LOW MOVING ACROSS THE SOUTHWESTERN U.S. THE TROPICAL
STORM IS EXPECTED TO MOVE TOWARD THE NORTHWEST OR WEST-NORTHWEST AT
A SLOWER FORWARD SPEED OVER THE NEXT COUPLE OF DAYS AS STEERING
CURRENTS WEAKEN. A TURN TOWARD THE NORTH IS FORECAST AROUND MIDWEEK
AS AN AMPLIFIED UPPER-LEVEL TROUGH MOVES ACROSS THE EASTERN PACIFIC.
THE LATEST NHC TRACK FORECAST HAS BEEN ADJUSTED WESTWARD ONCE AGAIN
TO REFLECT TRENDS IN THE GLOBAL AND REGIONAL HURRICANE MODEL
GUIDANCE. HOWEVER, THE TRACK STILL REMAINS NEAR THE EASTERN EDGE OF
THE GUIDANCE ENVELOPE, AND ADDITIONAL WESTWARD ADJUSTMENTS MAY BE
NEEDED IN SUBSEQUENT FORECAST CYCLES.
WESTERLY TO SOUTHWESTERLY WIND SHEAR AND RELATIVELY DRY MID-LEVEL
AIR ARE EXPECTED TO SUPPORT GRADUAL WEAKENING OVER THE NEXT SEVERAL
DAYS. BY MIDWEEK, THE UPPER-LEVEL TROUGH IS FORECAST TO PRODUCE A
SIGNIFICANT INCREASE IN WIND SHEAR, LEADING TO FURTHER WEAKENING. BY
LATE THIS WEEK, SIMULATED SATELLITE IMAGERY FROM THE ECMWF AND GFS
SUGGESTS THAT VANCE MAY STRUGGLE TO SUSTAIN ORGANIZED DEEP
CONVECTION. THE FORECAST CALLS FOR VANCE TO BECOME POST-TROPICAL BY
96 H AND DEGENERATE INTO A REMNANT LOW BY 120 H.
KEY MESSAGES:
1. ALTHOUGH THE THREAT OF IMPACTS TO MEXICO IS TRENDING DOWNWARD AS
THE FORECAST TRACK CONTINUES TO SHIFT WESTWARD AND AWAY FROM THE
COAST, UNCERTAINTY REMAINS IN BOTH THE TRACK AND INTENSITY
FORECASTS. INTERESTS IN SOUTHWESTERN MEXICO SHOULD CONTINUE TO
MONITOR THE PROGRESS OF VANCE.
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 COLIMA, NAYARIT, AND
SINALOA, ALONG WITH WESTERN PORTIONS OF MICHOACáN, JALISCO, AND
DURANGO, ESPECIALLY IN AREAS ALONG STEEP TERRAIN.
FORECAST POSITIONS AND MAX WINDS
INIT 25/2100Z 14.9N 104.2W 60 KT 70 MPH
12H 26/0600Z 15.0N 104.8W 60 KT 70 MPH
24H 26/1800Z 15.4N 105.5W 55 KT 65 MPH
36H 27/0600Z 16.0N 106.2W 50 KT 60 MPH
48H 27/1800Z 16.9N 106.6W 45 KT 50 MPH
60H 28/0600Z 17.7N 107.0W 45 KT 50 MPH
72H 28/1800Z 19.0N 107.2W 45 KT 50 MPH
96H 29/1800Z 21.0N 107.4W 40 KT 45 MPH...POST-TROPICAL
120H 30/1800Z 23.3N 107.2W 30 KT 35 MPH...POST-TROP/REMNT LOW
FORECASTER ADAMS
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