Tropical Storm MALAKAS Advisory lun, 19-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 30//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
    TYPHOON 18W (MALAKAS), LOCATED APPROXIMATELY 262 NM SOUTH-
SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON
SATELLITE EYE FIXES FROM RJTD AND PGTW WITH HIGH CONFIDENCE. THE
INTENSITY OF 105 KNOTS IS CONSISTENT WITH SUBJECTIVE DVORAK
INTENSITY ESTIMATES FROM THE SAME REPORTING AGENCIES, AS WELL AS
RECENT OBJECTIVE SATELLITE INTENSITY CONSENSUS ESTIMATES FROM CIMSS.
TY 18W HAS MAINTAINED INTENSITY OVER THE PAST SIX HOURS WHILE
TRACKING NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF A
SUBTROPICAL STEERING RIDGE. RECENT MULTISPECTRAL SATELLITE IMAGERY
SHOWS THE PRESENCE OF A 12 NM DIAMETER EYE. STRONG POLEWARD OUTFLOW
AND PASSAGE OVER WARM WATER HAVE ENABLED TY 18W TO MAINTAIN
INTENSITY OVER THE PAST SIX HOURS. ALTHOUGH THE SYSTEM HAS BEGUN TO
ENCOUNTER STRONG UPPER-LEVEL WESTERLY FLOW, STORM MOTION IN PHASE
WITH THE SHEAR VECTOR HAS PREVENTED NEGATIVE IMPACTS TO THE
CIRCULATION THUS FAR.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 18W WILL ACCELERATE NORTHEASTWARD ALONG THE POLEWARD
PERIPHERY OF THE CURRENT STEERING RIDGE THROUGH THE FORECAST PERIOD.
INTENSITY IS EXPECTED TO REMAIN FAIRLY STEADY OVER THE NEXT 12 HOURS
AS STRONG POLEWARD OUTFLOW CONTINUES TO COUNTERACT THE POTENTIALLY
NEGATIVE IMPACT OF INCREASING WESTERLY FLOW ALOFT. HOWEVER,
INCREASING VERTICAL WIND SHEAR AND PASSAGE OVER LAND AFTER TAU 12
WILL LEAD TO RAPID WEAKENING. THE SYSTEM WILL BEGIN EXTRATROPICAL
TRANSITION AROUND TAU 36 AS IT PASSES ALONG THE SOUTHERN COAST OF
HONSHU. HOWEVER, TY 18W IS EXPECTED TO DISSIPATE BELOW THE WARNING
THRESHOLD INTENSITY OF 25 KNOTS AS IT COMPLETES EXTRATROPICAL
TRANSITION AROUND TAU 72. NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT REGARDING THE FORECAST TRACK, WITH THE EXCEPTION OF THE
JAPANESE ENSEMBLE TRACKER, JENI, WHICH DEPICTS A TRACK ACROSS HONSHU
AND INTO THE SEA OF JAPAN, AND HWRF, WHICH DEPICTS A TRACK INTO
CENTRAL HONSHU AND INLAND DISSIPATION. THE CURRENT FORECAST FAVORS
THE MAJORITY TRACK GROUPING, AND LIES NEAR THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE.//
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