Tropical Storm MERANTI Advisory Mon Sep 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 16W (MERANTI) WARNING NR
16//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON 16W (MERANTI), LOCATED APPROXIMATELY 457 NM SOUTH
OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 12 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY HAS
INDICATED CONTINUED RAPID INTENSIFICATION SINCE 120600Z, WITH CLOUD
TOPS CONTINUING TO COOL AND THE DEEP CONVECTION SURROUNDING THE WELL-
DEFINED EYE BECOMING EVEN MORE SYMMETRIC. EYE TEMPERATURES HAVE ALSO
WARMED SIGNIFICANTLY, WITH THERMOMETRIC ESTIMATES OF OVER 18C IN THE
CENTER OF THE EYE. A 121247Z AMSU-B 89GHZ MICROWAVE IMAGE DEPICTS
THE PRESENCE OF MULTIPLE SPIRAL BANDS OF DEEP CONVECTION WRAPPING
INTO A WELL-DEFINED EYE. CONVECTIVE SYMMETRY AND BANDING CONTINUES
TO IMPROVE AS OF THIS WRITING. DVORAK INTENSITY ESTIMATES FROM BOTH
PGTW AND RJTD HAVE RISEN TO T7.5. GIVEN THE ABOVE ANALYSIS, THE
CURRENT INTENSITY IS ASSESSED AT 155 KNOTS. STY 16W IS CURRENTLY IN
AN EXTREMELY FAVORABLE ENVIRONMENT FOR THE MAINTENANCE OF AN INTENSE
SUPER TYPHOON, WITH EXCELLENT RADIAL OUTFLOW IN ALL QUADRANTS, VERY
LOW VERTICAL WIND SHEAR (LESS THAN 5 TO 10 KNOTS), AND WARM SSTS (30
TO 31C). CURRENT WIND RADII WERE ADJUSTED OUTWARD BASED ON A 120928
WINDSAT PASS. 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 STR. THE MAJORITY
OF MODEL GUIDANCE HAS NOW SETTLED ON A TRACK THAT TAKES THE SYSTEM
TOWARD SOUTHERN TAIWAN OR ACROSS THE NORTHERN PORTION OF THE LUZON
STRAIT. THE ONLY EXCEPTIONS ARE THE EGRR, JGSM, AND JENS TRACKERS,
WHICH INDICATE A MORE SOUTHERN TRACK. THE CURRENT JTWC FORECAST
PREFERS THE SLIGHTLY MORE NORTHERN SOLUTION, GIVEN THE RECENT MOTION
TOWARD THE NORTHWEST. BEYOND TAU 36, TRACK SHIFTS DUE TO VORTEX
INTERACTION WITH THE CENTRAL MOUNTAIN RANGE OF TAIWAN ARE POSSIBLE,
AND THE INTENSITY FORECAST WILL DEPEND ON THESE TRACK SHIFTS. STY
16W IS LIKELY APPROACHING IS THERMODYNAMIC MAXIMUM POTENTIAL
INTENSITY, SO SHORT-TERM FLUCTUATIONS IN INTENSITY ARE LIKELY OVER
THE NEXT 24 HOURS, DRIVEN PREDOMINANTLY BY EYEWALL REPLACEMENT
CYCLES. A SLOW WEAKENING IS FORECAST AFTER TAU 24 AS SSTS BEGIN TO
GRADUALLY COOL AND LAND INTERACTION WITH TAIWAN COMMENCES.
   C. AFTER TAU 72, DYNAMIC MODEL GUIDANCE SUGGEST THAT STY 16W WILL
CROSS THE TAIWAN STRAIT AS A WEAKER SYSTEM AND MAKE A SECOND
LANDFALL OVER MAINLAND CHINA BY AROUND TAU 60. WEAKENING AND
DISSIPATION OVER LAND IS EXPECTED THEREAFTER, WITH A POLEWARD TURN
DUE TO A WEAKNESS IN THE STR. 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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