Tropical Storm MERANTI Advisory lun, 12-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 16W (MERANTI) WARNING NR
15//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON 16W (MERANTI), LOCATED APPROXIMATELY 493 NM SOUTH
OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 11 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY AND A
120551Z MHS 89GHZ MICROWAVE IMAGE DEPICT AN INTENSE SUPER TYPHOON
WITH DEEP CONVECTION, MULTIPLE SPIRAL BANDS, AND A SMALL EYE LESS
THAN 10NM IN DIAMETER. THERE IS EXCELLENT CONFIDENCE IN THE CURRENT
POSITION AND RECENT TRACK MOTION. UPPER-LEVEL ANALYSIS INDICATES AN
ENVIRONMENT OF LOW VERTICAL WIND SHEAR AND EXCELLENT RADIAL OUTFLOW.
TOGETHER WITH AMPLE WARM OCEAN WATER, STY 16W HAS UNDERGONE RAPID
INTENSIFICATION. THE CURRENT INTENSITY OF 130 KNOTS IS BASED ON
DVORAK INTENSITY ESTIMATES OF T6.5 FROM ALL AGENCIES. STY 16W
CONTINUES TO TRACK TOWARD THE WEST-NORTHWEST UNDER THE STEERING
INFLUENCE OF A SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE IN THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 72, STY 16W WILL TRACK GENERALLY WEST-
NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE DEEP-LAYERED
SUBTROPICAL RIDGE (STR). THE MAJORITY OF DYNAMIC MODEL GUIDANCE
SUGGEST A MORE WESTWARD TRACK THROUGH THE LUZON STRAIT. HOWEVER, THE
OFFICIAL JTWC FORECAST LIES ON THE POLEWARD SIDE OF THE ENVELOPE OF
TRACK GUIDANCE GIVEN THE RECENT MOTION BEING MORE TOWARD THE
NORTHWEST. FURTHER INTENSIFICATION IS POSSIBLE, AND STY 16W IS
EXPECTED TO REACH A PEAK INTENSITY OF 140 KNOTS FROM TAU 12 TO 24,
FOLLOWED BY SOME FLUCTUATIONS IN INTENSITY AND SOME WEAKENING AS THE
CIRCULATION INTERACTS WITH THE TOPOGRAPHY OF SOUTHERN TAIWAN. MORE
SIGNIFICANT CHANGES TO THE TRACK FORECAST MAY BE NECESSARY WITH
FUTURE ADJUSTMENTS TO THE TRACK FORECAST.
   C. AFTER TAU 72, THE MAJORITY OF DYNAMIC MODEL GUIDANCE TAKES STY
16W THROUGH THE LUZON STRAIT AND TAIWAN STRAIT TOWARD A SECOND
LANDFALL IN MAINLAND CHINA, UNDER THE STEERING INFLUENCE OF THE STR
AXIS TO THE NORTH. AFTER LANDFALL, THERE ARE DIFFERENCES IN TIMING
OF A POTENTIAL TURN TOWARD THE NORTH, WITH SOME MODELS CONTINUING TO
SUGGEST A MORE WESTWARD MOTION. REGARDLESS, THE CIRCULATION OF STY
16W SHOULD WEAKEN QUICKLY, PARTICULARLY IF IT EXPERIENCES
SIGNIFICANT STRUCTURAL DISRUPTIONS FROM THE CENTRAL MOUNTAIN RANGE
OF TAIWAN. DISSIPATION IS EXPECTED TO OCCUR AROUND TAU 96. DUE TO
THE LARGE MODEL SPREAD BEYOND 48 HOURS, THERE IS LOW CONFIDENCE IN
THE JTWC TRACK FORECAST BEYOND THAT TIME.//
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