Tropical Storm JELAWAT Advisory Sat Sep 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (JELAWAT) WARNING NR 37//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 18W (JELAWAT), LOCATED APPROXIMATELY 160 NM NORTHEAST OF
KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 18
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY (EIR) SHOWS TY 18W HAS UNDERGONE A SLIGHT WEAKENING TREND
ABOUT FIVE HOURS PREVIOUSLY, BUT HAS RECENTLY SEEN A PINHOLE EYE RE-
DEVELOP IN THE LAST HOUR. THE CURRENT POSITION IS BASED ON THE EIR
AND PGTW FIX. THE CURRENT INTENSITY OF 85 KNOTS IS BASED ON A
VARIETY OF DVORAK FIXES FROM PGTW, KNES AND RJTD RANGING FROM 77 TO
90 KNOTS. UPPER LEVEL ANALYSIS INDICATES THE EQUATORWARD OUTFLOW
CHANNEL REMAINS HINDERED, WITH THE POLEWARD CHANNEL CONTINUES
PROVIDING AMPLE EXHAUST FOR THE SYSTEM. A RECENT SEA SURFACE
TEMPERATURE (SST) ANALYSIS INDICATED WEAK UPWELLING ALONG THE
EASTERN COAST OF THE RYUKYU ISLANDS COULD BE A FACTOR IN BRIEF
WEAKENING OBSERVED. TY 18W CONTINUES TO TRACK ALONG THE NORTHWESTERN
PERIPHERY OF AN EXTENSION OF THE SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 18W WILL CONTINUE TO TRACK ALONG THE NORTHWESTERN PERIPHERY
OF THE STR TOWARDS THE SOUTHERN COAST OF HONSHU, MAKING LANDFALL
AROUND 30/09Z BASED ON THE CURRENT TRACK SPEEDS. INCREASING VERTICAL
WIND SHEAR, DECREASING SSTS, AND EVENTUALLY INTERACTION WITH LAND
WILL CAUSE A STEADY WEAKENING OF THE SYSTEM. BY TAU 24 TY 18W IS
EXPECTED TO BEGIN EXTRA-TROPICAL TRANSITION, AND WILL BE A FULLY
COLD-CORE SYSTEM BY TAU 48. LAND INTERACTION AFTER TAU 24 AND
INCREASING MID-LATITUDE INTERACTION WILL BE THE PRIMARY FACTORS
LEADING TO THE QUICK TRANSITION OF THE SYSTEM. MODEL GUIDANCE
REMAINS CONSISTENT WITH A MORE NORTHWARD TRACK OVER THE MOUNTAINOUS
REGION OF HONSHU. THE CURRENT FORECAST KEEPS THE TRACK SOUTH OF
CONSENSUS AND SLIGHTLY FASTER. CONFIDENCE IN THE FORECAST TRACK
REMAINS HIGH.//
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