Tropical Storm MALAKAS Advisory Sa, 17.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 22//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 18W (MALAKAS), LOCATED APPROXIMATELY 249 NM WEST-
SOUTHWEST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWARD AT 12 KNOTS
OVER THE PAST SIX HOURS. ANIMATED HIGH RESOLUTION VISIBLE SATELLITE
IMAGERY INDICATES A CLOUD-FILLED AND RAGGED EYE 10NM EYE. A 162249Z
SSMIS 91 GHZ IMAGE DEPICTS A VERY WEAK EYE FEATURE WITH THE SYSTEM
BECOMING MORE ASYMMETRICAL OVER THE PAST SIX HOURS, WITH DEEP
CONVECTION LIMITED TO THE EASTERN HALF OF THE SYSTEM. THE INITIAL
POSITION IS BASED ON SATELLITE EYE FIXES FROM PGTW AND RJTD, AND
RADAR FIX DATA BASED ON TAIWAN RADAR DATA WITH GOOD CONFIDENCE. THE
INITIAL INTENSITY IS ASSESSED AT 105 KNOTS FROM DVORAK INTENSITY
ESTIMATES FROM RJTD AND PGTW RANGING FROM T5.0 (90 KTS) TO T5.5 (105
KTS). UPPER-LEVEL ANALYSIS INDICATES THAT THE POINT SOURCE
PREVIOUSLY OVER TY 18W HAS MOVED OFF TO THE WEST, AND NOW IS
PRODUCING SOME PRESSURE ON THE WESTERN SIDE OF THE SYSTEM,
SUPPORTING THE WEAKENING TREND. EQUATORWARD OUTFLOW REMAINS STRONG
AND SEA SURFACE TEMPERATURES REMAIN VERY FAVORABLE NEAR 29 TO 30
CELSIUS. TY MALAKAS IS TRACKING NORTHWARD ALONG THE PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE CENTERED TO THE TO THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 18W IS FORECAST TO CONTINUE TO TRACK GENERALLY NORTHWARD
OVER THE NEXT 12 HOURS AS IT APPROACHES THE AXIS OF A DEEP-LAYER
STEERING RIDGE CENTERED TO THE EAST-NORTHEAST. BEYOND TAU 12 THE
SYSTEM WILL ROUND THE RIDGE AXIS AND BEGIN TO TRACK NORTHEASTWARD AS
THE STEERING RIDGE RECEDES EASTWARD AHEAD OF A MAJOR SHORTWAVE
TROUGH APPROACHING FROM THE WEST, ACCELERATING AFTER TAU 48. AS THE
POINT SOURCE CONTINUES TO MOVE WESTWARD AND WEAKEN, POLEWARD OUTFLOW
WILL REMAIN WEAK THROUGH TAU 48, PRODUCING A SINGLE-CHANNEL OUTFLOW
SCENARIO, AND ALLOWING FOR A SLOW WEAKENING TREND THROUGH TAU 48.
BETWEEN TAUS 48 AND 72, THE SYSTEM WILL BEGIN TO TAP INTO THE STRONG
POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH THE MID-LATITUDE WESTERLY
FLOW, ALLOWING THE SYSTEM TO MAINTAIN INTENSITY FOR SHORT PERIOD
THROUGH TAU 72 BEFORE ENCOUNTERING INCREASING VERTICAL WIND SHEAR.
   C. IN THE EXTENDED TAUS, TY 18W WILL ACCELERATE TOWARDS THE
NORTHEAST, MAKING LANDFALL IN SOUTHERN KYUSHU BETWEEN TAU 72 AND 96,
WEAKENING RAPIDLY AS IT ENCOUNTERS HIGH VERTICAL WIND SHEAR
ASSOCIATED WITH THE MID-LATITUDE WESTERLY JET AND LAND INTERACTION
EFFECTS. THE SYSTEM WILL BEGIN TO UNDERGO EXTRA-TROPICAL TRANSITION
BY TAU 96, WHILE SIMULTANEOUSLY DISSIPATING OVER HONSHU. DYNAMIC
MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48, WITH INCREASING
UNCERTAINTY IN THE ALONG-TRACK SPEEDS AFTER TAU 72. THE CURRENT
TRACK FORECAST LIES NEAR THE MULTI-MODEL CONSENSUS GIVEN THE NOTED
MODEL UNCERTAINTY IN TRACK SPEED, THERE IS LOW CONFIDENCE IN THE
EXTENDED TRACK FORECAST.//
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