Tropical Storm MERANTI Advisory сб, 10.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN)
WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 16W (SIXTEEN), LOCATED APPROXIMATELY 205
NM WEST-NORTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY INDICATES DEEP CONVECTION INCREASING IN AREAL EXTENT,
HOWEVER, THE BULK OF THE CONVECTION IS CONFINED TO THE SOUTHERN SEMI-
CIRCLE OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) DUE TO NORTHERLY
VERTICAL WIND SHEAR (VWS). A 091538Z GCOM 36GHZ IMAGE AND A 091720Z
AMSU-B 89GHZ IMAGE BOTH DEPICT AN EXPOSED LLCC WITH A CURVED DEEP
CONVECTIVE BAND OVER THE SOUTHWEST QUADRANT OF THE LLCC. THERE IS
FAIR CONFIDENCE IN THE CURRENT POSITION BASED ON THE GCOM 36GHZ
IMAGE, WHICH SHOWS CONVECTIVE BANDING WRAPPING INTO AN ELONGATED BUT
DEFINED LLCC. THE CURRENT INTENSITY HAS BEEN HELD AT 30 KNOTS BASED
ON THE CONVECTIVE SIGNATURE, A RECENT ASCAT IMAGE AND A PGTW DVORAK
ESTIMATE OF T2.0 (30 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. TD 16W IS FORECAST TO TRACK 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, TD 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
450-NM SPREAD IN MODEL TRACKER SOLUTIONS. WITH THE EXCEPTION OF THE
UKMET, 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 TD 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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