Tropical Storm FENGSHEN Advisory Per, 14.11.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (FENGSHEN)
WARNING NR 010//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 26W (FENGSHEN), LOCATED APPROXIMATELY 328 NM EAST
OF ALAMAGAN, HAS TRACKED WESTWARD AT 14 KNOTS OVER THE PAST SIX
HOURS. THE CURRENT POSITION IS BASED ON A 131800Z PGTW SATELLITE FIX
AND RECENT MICROWAVE SATELLITE IMAGERY INCLUDING A 131513Z AMSR2 PASS
AND A 131844Z SSMIS PASS. TS 26W IS TRACKING ALONG THE PERIPHERY OF A
SUBTROPICAL STEERING RIDGE SITUATED TO THE NORTH. DEEP CONVECTIVE
BANDING IS PRESENT ALONG THE EASTERN PORTION OF THE SYSTEM, AND THE
LOW-LEVEL CIRCULATION PARTIALLY EXPOSED TO THE NORTHWEST OF THE
PRIMARY CONVECTION. TS 26W IS LOCATED IN AN AREA OF LOW TO MODERATE
(10-15 KNOTS) VERTICAL WIND SHEAR, WARM SEA SURFACE TEMPERATURES
(28-29C) AND MODERATE WESTWARD AND EQUATORWARD DIFFLUENCE ALOFT.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS CHANGED SIGNIFICANTLY FOR THE
EXTENDED FORECAST PERIOD. THE PREVIOUS FORECAST CALLED FOR CONTINUED
EASTWARD MOTION AND EXTRATROPICAL TRANSITION ASSOCIATED WITH MID-
LATITUDE TROUGH INTERACTION. THE CURRENT FORECAST CALLS FOR WEAKENING
FOLLOWED BY A WESTWARD TURN DURING THE EXTENDED FORECAST PERIOD. THE
SYSTEM IS NOW EXPECTED TO WEAKEN UNDER STRONG VERTICAL WIND SHEAR
BETWEEN TAU 72 AND TAU 120, REMAIN SEPARATED FROM THE MID-LATITUDE
FLOW PATTERN AND BACKTRACK AS IT FOLLOWS THE LOWER-LEVEL FLOW.
   B. TS 26W IS EXPECTED TO CONTINUE TRACKING AROUND THE CURRENT
STEERING RIDGE PERIPHERY THROUGH TAU 72. LOW VERTICAL WIND SHEAR,
PASSAGE OVER WARM WATER AND MODERATE DIVERGE ALOFT WILL LIKELY FUEL
STEADY INTENSIFICATION IN THE NEAR TERM. HOWEVER, AFTER THE
CIRCULATION ROUNDS THE STEERING RIDGE, WESTERLY VERTICAL WIND SHEAR
IS EXPECTED TO INCREASE SIGNIFICANTLY AND DRIVE A SUSTAINED WEAKENING
TREND. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT WITH THIS
OVERALL SCENARIO THROUGH TAU 72, LENDING HIGH CONFIDENCE TO THAT
PORTION OF THE TRACK FORECAST.
   C. IN THE EXTENDED FORECAST PERIOD, TS 26W IS EXPECTED TO WEAKEN
STEADILY UNDER STRONG WESTERLY VERTICAL WIND SHEAR. ALL AVAILABLE
NUMERICAL MODEL GUIDANCE NOW INDICATES THAT THE SYSTEM WILL REMAIN
SEPARATED FROM A MID-LATITUDE TROUGH PASSING TO THE NORTH DURING THIS
TIME FRAME. THE PRIMARY STEERING INFLUENCE WILL SHIFT TO A LOWER-
LEVEL RIDGE AS TS 26W WEAKENS, RESULTING IN A HOOK BACK TO THE WEST.
NUMERICAL MODELS VARY WIDELY IN THEIR DEPICTIONS OF THE RATE OF
WEAKENING AND TRACK SHIFT DURING THE EXTENDED PERIOD. THE CURRENT
TRACK FORECAST LIES NEAR THE MULTI-MODEL CONSENSUS, WITH LOW
CONFIDENCE IN THE EXTENDED PERIOD BASED ON THE NOTED MODEL SPREAD.//
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