Tropical Storm MERANTI Advisory Sat Sep 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (MERANTI)
WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 16W (MERANTI), LOCATED APPROXIMATELY 380 NM NORTH-
NORTHWEST OF ULITHI, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A CONVECTIVE STRUCTURE THAT IS GRADUALLY BECOMING
BETTER ORGANIZED. ALTHOUGH A 100948Z SSMIS 91GHZ MICROWAVE IMAGE
CONTINUES TO INDICATE A LOW-LEVEL CIRCULATION CENTER (LLCC) THAT
REMAINS DISPLACED TO THE NORTHWEST OF THE DEEPEST CONVECTION, THE
VERTICAL WIND SHEAR APPEARS TO BE RELAXING. THE CURRENT
POSITION IS PLACED WITH GOOD CONFIDENCE WITH THE 101148Z ASCAT PASS,
WHICH ALSO DEPICTS A WIND FIELD THAT IS STILL BROADER TO THE EAST OF
THE LLCC. THE SYSTEM REMAINS UNDER THE STEERING INFLUENCE OF A
BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTH, MODULATED BY THE
GRADUAL WEAKENING OF A TUTT CELL. ENVIRONMENTAL CONDITIONS ARE
MARGINALLY FAVORABLE FOR CONTINUED DEVELOPMENT WITH WARM SSTS AND
MODERATE EQUATORIAL OUTFLOW.
3. FORECAST REASONING.
   A. THE FORECAST TRACK AT EXTENDED TAUS HAS BEEN SHIFTED FURTHER
WESTWARD.
   B. TS 16W IS FORECAST TO CONTINUE TRACKING TOWARD THE WEST-
NORTHWEST UNDER THE INFLUENCE OF A BUILDING STR THROUGH THE FORECAST
PERIOD. SOME SLOW INTENSIFICATION IS EXPECTED FOR THE NEXT 12 TO 36
HOURS. THEREAFTER, THE TUTT CELL TO THE NORTH-NORTHEAST OF TS 16W
SHOULD WEAKEN AND ENABLE THE DEVELOPMENT OF A MUCH MORE FAVORABLE
UPPER-TROPOSPHERIC OUTFLOW PATTERN OVER THE SYSTEM. MORE RAPID
INTENSIFICATION IS LIKELY BEYOND TAU 36. DYNAMIC MODEL GUIDANCE
REMAINS IN FAIRLY GOOD AGREEMENT IN BOTH TRACK AND SPEED DURING THIS
PORTION OF THE FORECAST.
   C. IN THE EXTENDED FORECAST PERIOD, DYNAMICAL MODEL GUIDANCE
CONTINUES TO SHIFT TOWARD THE WEST, GUIDANCE NOW SPLIT BETWEEN AN
IMPACT TO TAIWAN AND A TRACK FURTHER SOUTH OVER THE LUZON STRAIT.
THE JTWC FORECAST SUGGESTS A TURN TOWARD THE NORTHWEST AT TAUS 96
AND 120, BUT THERE IS LARGE UNCERTAINTY IN THE TRACK FORECAST BEYOND
72 HOURS. THE EVENTUAL EVOLUTION OF THE STEERING FLOW WILL DEPEND IN
PART ON THE RATE AT WHICH THE TUTT CELL TO THE NORTH-NORTHEAST OF TS
16W WEAKENS. THE INTENSITY FORECAST SUBSEQUENTLY DEPENDS ON THE
EVENTUAL TRACK OF TS 16W, WITH AN IMPACT TO TAIWAN IMPLYING
SIGNIFICANT WEAKENING BEGINNING AROUND TAU 96. THE ALTERNATE
SCENARIO OF A TRACK FURTHER TO THE SOUTH WOULD RESULT IN A STRONGER
INTENSITY AT THE EXTENDED RANGE. DUE TO THE LARGE MODEL SPREAD
BEYOND 72 HOURS, THERE IS LOW CONFIDENCE IN THE JTWC TRACK
FORECAST.//
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