WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (MEKKHALA) WARNING 
NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (MEKKHALA), LOCATED APPROXIMATELY 262 NM 
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 
09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY 
SHOWS THE SYSTEM HAS MAINTAINED A CENTRAL DENSE OVERCAST FEATURE 
THROUGHOUT LANDFALL IN NORTHERN SAMAR. A 171243Z METOP-A AND 171109Z 
SSMIS MICROWAVE IMAGES REVEAL THAT THE DEEPEST CONVECTION IS 
CONCENTRATED ON THE WESTERN HALF OF THE SYSTEM, WITH A LARGE WIND 
FIELD AS SHOWN IN THE 170940Z WINDSAT MICROWAVE. THE INITIAL 
INTENSITY OF 55 KNOTS IS BASED ON OBSERVATIONS AND THE WEAKENING 
STATE OF THE SYSTEM DUE TO LAND INTERACTION. UPPER-LEVEL ANALYSIS 
CONTINUES TO DEPICT A FAVORABLE ENVIRONMENT WITH MODERATE (10 TO 20 
KNOTS) EASTERLY VERTICAL WIND SHEAR IN-PHASE WITH THE SYSTEM MOTION 
AND GOOD UPPER-LEVEL DIVERGENCE. THE CYCLONE IS CURRENTLY TRACKING 
ALONG THE SOUTHWESTERN PERIPHERY OF AN ELONGATED SUBTROPICAL RIDGE 
(STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS MEKKHALA WILL CONTINUE TO TRACK TO THE NORTHWEST UNDER THE 
INFLUENCE OF THE STR. EXPECT FURTHER DECAY OF THE SYSTEM AS IT RUNS 
ALONG THE BICOL REGION AND INTO CENTRAL LUZON PAST TAU 24. EXPECT 
STEADY DEGENERATION DUE TO LAND INTERACTION FOR THE DURATION OF THE 
FORECAST WITH THE SYSTEM EMERGING FROM LUZON AS A DISSIPATED 
TROPICAL DEPRESSION. THERE IS A BIFURCATION IN THE FORECAST PAST TAU 
36 WITH MANY MODELS RE-CURVING THROUGH EASTERN LUZON AND A FEW MORE 
FLAT SCENARIOS. DUE TO THIS LARGE SPREAD, THE JTWC TRACK IS LAID 
WITH LOW CONFIDENCE AND CLOSE TO THE MULTI-MODEL CONSENSUS.//
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