Tropical Storm MERANTI Advisory Sa, 10.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (SIXTEEN)
WARNING NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (SIXTEEN), LOCATED APPROXIMATELY 294 NM
WEST-NORTHWEST OF NAVSTA GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS AN EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
DISPLACED OVER THE NORTHERN EDGE OF A LARGE AREA OF CURVED DEEP
CONVECTION DUE TO NORTHERLY VERTICAL WIND SHEAR (VWS). A 092352Z
METOP-B 89GHZ IMAGE SHOWS DEEP CONVECTIVE BANDING WRAPPING INTO THE
SOUTHEAST QUADRANT OF THE LLCC. THERE IS GOOD CONFIDENCE IN THE
CURRENT POSITION BASED ON THE MSI. THE CURRENT INTENSITY IS ASSESSED
AT 35 KNOTS BASED ON A PGTW DVORAK ESTIMATE OF T2.5 (35 KNOTS).
ENVIRONMENTAL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT
WITH LOW (5-10 KNOT) VWS, WEAK RADIAL OUTFLOW, AND WARM (29C) SST.
THE SYSTEM HAS STARTED TO TRACK WESTWARD TO WEST-NORTHWESTWARD UNDER
THE STEERING INFLUENCE OF A BUILDING LOW LEVEL SUBTROPICAL RIDGE
(STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 16W IS FORECAST TO TRACK WEST-NORTHWESTWARDB TO
NORTHWESTWARD UNDER THE BUILDING STR THROUGHOUT THE FORECAST PERIOD.
THE GENERALLY FAVORABLE ENVIRONMENTAL CONDITIONS WILL ALLOW FOR A
STEADY INTENSIFICATION OVER THE NEXT 36 HOURS. AFTERWARDS, INCREASED
VWS DUE TO NORTHEASTERLY FLOW ASSOCIATED WITH THE EASTERN EDGE OF AN
UPPER LEVEL STR POSITIONED OVER CHINA WILL TEMPER THE RATE OF
INTENSIFICATION. BEYOND TAU 48, THIS RIDGE WILL WEAKEN, DECREASING
THE VWS ONCE AGAIN. DYNAMIC MODEL GUIDANCE REMAINS IN FAIRLY GOOD
AGREEMENT DURING THIS PORTION OF THE FORECAST, WITH ONLY SMALL
DIFFERENCES IN THE FORWARD SPEED OF THE SYSTEM.
   C. IN THE EXTENDED FORECAST PERIOD, TS 16W WILL BEGIN TO TURN
POLEWARD AS IT TRACKS ALONG THE SOUTHWEST PERIPHERY OF THE STR.
BEYOND TAU 72, IMPROVED VWS AND OUTFLOW ASSOCIATED WITH A MID-
LATITUDE TROUGH APPROACHING FROM THE WEST, COMBINED WITH INCREASED
SSTS AND HIGH OCEAN HEAT CONTENT, WILL SUPPORT AN INCREASED
INTENSIFICATION RATE WITH THE POSSIBILITY OF RAPID INTENSIFICATION.
THERE IS A LARGE DEGREE OF UNCERTAINTY IN THE EXTENDED TAUS WITH A
290-NM SPREAD IN MODEL TRACKER SOLUTIONS. WITH THE EXCEPTION OF THE
UKMET AND COAMPS-TC, ALL THE OTHER MODELS SUPPORT A RE-CURVE
SCENARIO WITH SIGNIFICANT DIFFERENCES IN THE RE-CURVE POINT AND
TRACK SPEEDS. MODEL FIELDS INDICATE AN APPROACHING SHORTWAVE TROUGH
WILL ERODE THE STR OVER EASTERN CHINA ALLOWING TS 16W TO RE-CURVE
POLEWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE EASTERN
STR, POSITIONED SOUTH OF JAPAN. TRACK SPEEDS LIKELY WILL REMAIN SLOW
THROUGH TAU 120 DUE TO THE LACK OF A DYNAMIC, DEEP SHORTWAVE TROUGH
AND WEAK BAROCLINICITY. THE JTWC TRACK FORECAST IS POSITIONED NEAR
THE MULTI-MODEL CONSENSUS (CONW) THROUGH TAU 72 AND THEN RIGHT OF
CONW FAVORING ALL OF THE GLOBAL MODELS WHICH SHOW A RECURVE
SCENARIO. DUE TO INCREASING UNCERTAINTY AND LARGE MODEL SPREAD IN
THE RE-CURVE PHASE, THERE IS NOW LOW CONFIDENCE IN THE JTWC TRACK
FORECAST.//
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