WDPN31 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (MEKKHALA) WARNING 
NR 09//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (MEKKHALA), LOCATED APPROXIMATELY 277 NM
NORTH-NORTHWEST OF KOROR, PALAU, HAS TRACKED WESTWARD AT 08 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY (EIR) REVEALS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION 
CENTER (LLCC) WITH THE BULK OF THE DEEP CONVECTION CONFINED TO THE 
WESTERN SEMI-CIRCLE. A 150925Z SSMIS 37GHZ MICROWAVE PASS REVEALED A 
LOOSELY WRAPPING LLCC AS THE OVERALL CONVECTIVE STRUCTURE REMAINS 
UNCHANGED. THE CURRENT POSITION IS BASED ON THE EIR ANIMATION AND 
PERSISTENCE FROM THE MICROWAVE PASS WITH FAIR CONFIDENCE. THE 
CURRENT INTENSITY REMAINS AT 35 KTS BASED ON THE UNCHANGED STRUCTURE 
AND DVORAK INTENSITY ESTIMATES OF THE SAME VALUE FROM PGTW AND KNES. 
UPPER LEVEL ANALYSIS CONTINUES TO SHOW THAT TS 01W REMAINS IN A 
MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE (15-20 KNOTS) 
VERTICAL WIND SHEAR (VWS) WHICH IS BEING OFFSET BY GOOD POLEWARD 
OUTFLOW. TS MEKKHALA IS TRACKING WEST-NORTHWESTWARD ALONG THE 
SOUTHERN PERIPHERY OF A LOW- TO MID-LEVEL REFLECTION OF THE 
SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 36, TS 01W WILL CONTINUE TO TRACK GENERALLY WEST 
UNDER THE SOUTHERN PERIPHERY OF THE STR. AFTER TAU 36, A BREAK IN 
THE STR WILL ALLOW THE SYSTEM TO TURN SLIGHTLY MORE WEST-NORTHWEST 
AS IT MAKES LANDFALL ACROSS THE CENTRAL PHILLIPINE ISLANDS. TS 
MEKKHALA IS FORECAST TO SLOWLY INTENSIFY THROUGH TAU 36 REACHING A 
PEAK INTENSITY OF 50 KNOTS PRIOR TO MAKING LANDFALL. AFTER TAU 36, 
THE SYSTEM WILL WEAKEN DUE TO THE FRICTIONAL EFFECTS OF LAND, 
INCREASED VWS, AND ENCOUNTERING MORE STABLE AIR ASSOCIATED WITH THE 
PERSISTENT NORTHEASTERN SURGE. THERE IS A FAIR AMOUNT OF UNCERTAINTY 
IN THE TRACK AFTER LANDFALL AS THE NUMERIC MODEL GUIDANCE REMAINS 
SPREAD DUE TO DISAGREEMENT IN THE INTENSITY OF THE SYSTEM AND THE 
ORIENTATION OF THE STR. THERE IS A POSSIBILITY THAT THIS SYSTEM MAY 
DISSIPATE OVER THE ISLANDS BY TAU 72.
   C. AFTER TAU 72, TS MEKKHALA IS EXPECTED TO TRACK WEST INTO THE 
SOUTH CHINA SEA AS A WEAKENED TROPICAL DEPRESSION. THE NUMERIC MODEL 
GUIDANCE REMAINS WIDELY SPREAD AND ERRATIC AS PREVIOUSLY MENTIONED. 
GFS HAS SWITCHED BACK TO THE NORTH, ALONG WITH EGRR AND THE JAPANESE 
ENSEMBLE IN A HIGHLY UNLIKELY NORTHWARD TURN INTO THE SURGE. COAMPS-
TC AND GFDN REMAIN ON A WEST-SOUTHWEST TRACK AS THEY REVEAL A WEAKER 
THAN FORECAST SYSTEM. THE JTWC TRACK LIES IN CLOSE AGREEMENT WITH 
THE ECMWF AND GFS ENSEMBLE SOLUTION AS THEY BEST REPRESENT THE 
INTENSITY FORECAST. DUE TO THIS LARGE VARIATION IN MODEL SOLUTIONS, 
THE CONFIDENCE IN THE JTWC FORECAST TRACK REMAINS LOW.//
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