WDPN31 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (MEKKHALA)
WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 01W (MEKKHALA), LOCATED APPROXIMATELY 802 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 14
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS SPIRAL BANDING WRAPPING BENEATH AN AREA OF DEEP
CONVECTION DISPLACED TO THE NORTHWEST OF THE LOW-LEVEL CIRCULATION
CENTER (LLCC). A 142242Z SSMIS 91GHZ IMAGE AND A 142127Z WINDSAT
37GHZ IMAGE REVEAL WELL-DEFINED SHALLOW BANDING WRAPPING INTO THE
LLCC WITH THE BULK OF DEEP CONVECTION SHEARED TO THE NORTHWEST. THE
CURRENT POSITION IS BASED ON THE AFOREMENTIONED MICROWAVE IMAGERY
AND THE PGTW AND RJTD FIXES WITH FAIR CONFIDENCE. THE CURRENT
INTENSITY WAS INCREASED TO 35 KTS, HEDGED SLIGHTLY ABOVE DVORAK
INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM ALL AGENCIES, DUE TO THE
SYSTEM'S IMPROVED STRUCTURE. UPPER LEVEL ANALYSIS CONTINUES TO SHOW
THAT TS 01W IS IN A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE
(15-20 KNOTS) VERTICAL WIND SHEAR (VWS) BEING OFFSET BY EXCELLENT
POLEWARD OUTFLOW. TS MEKKHALA IS TRACKING WEST-NORTHWESTWARD ALONG
THE SOUTHERN PERIPHERY OF A LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TS 01W WILL CONTINUE TO TRACK WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR LOCATED TO THE NORTH THROUGH TAU 48.
AFTER TAU 48, THE SYSTEM WILL TURN SLIGHTLY TO THE NORTHWEST TOWARDS
A BREAK IN THE STR. TS MEKKHALA IS FORECAST TO SLOWLY INTENSIFY
THROUGH TAU 48 REACHING A PEAK INTENSITY OF 50 KNOTS PRIOR TO MAKING
LANDFALL OVER THE CENTRAL PHILIPPINES. BEYOND TAU 48, THE TS WILL
WEAKEN AS IT ENCOUNTERS THE PHILIPPINES AND INTERACTS WITH THE
NORTHEASTERLY SURGE EVENT. THE DYNAMIC GUIDANCE IS IN BETTER
AGREEMENT WITH A WESTWARD TRACK THROUGH TAU 48, HOWEVER, THE MODELS
CONTINUE TO SHOW A SIGNIFICANT DIVERGENCE THEREAFTER WITH A SPREAD
OF 365 NM AT TAU 72.
C. AFTER TAU 72, TS MEKKHALA IS EXPECTED TO SHIFT TO A SLIGHT
NORTHWESTWARD TRAJECTORY AND THE SYSTEM WILL CONTINUE TO WEAKEN AS
IT ENCOUNTERS INCREASED VWS AND MORE STABLE AIR ASSOCIATED WITH THE
PERSISTENT NORTHEASTERLY SURGE. AS MENTIONED ABOVE, THE DYNAMIC
MODEL GUIDANCE CONTINUES TO DIVERGE WITH A WIDE RANGE OF SOLUTIONS,
HOWEVER, GFS HAS SHIFTED THEIR TRACK TO COME MORE IN-LINE WITH THE
MAJORITY OF MODEL GUIDANCE. JENS AND EGRR CONTINUE TO RECURVE
THE SYSTEM SHARPLY NORTHWARD AFTER TAU 72 AND GFDN CONTINUES TO
TRACK A MUCH WEAKER SYSTEM (PEAK INTENSITY ONLY 30 KNOTS) WEST-
SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE LOW-LEVEL
NORTHEASTERLY FLOW. THE JTWC FORECAST IS POSITIONED WITHIN THE BULK
OF MODEL GUIDANCE, WHICH TRACKS TS 01W OVER THE CENTRAL TO
NORTHERN PHILIPPINES ALONG THE SOUTHWESTERN PERIPHERY OF THE STR.
BASED ON THE EXPECTED INTENSIFICATION TO NEAR 50 KNOTS, THIS TRACK
IS ASSESSED AS THE MOST LIKELY SOLUTION. DUE TO THE PERSISTENT LOW-
LEVEL RIDGE POSITIONED OVER THE EAST CHINA SEA AND NORTHEASTERLY
FLOW, A RECURVE SCENARIO IS HIGHLY UNLIKELY, THEREFORE, THE REMNANTS
OF TS 01W ARE EXPECTED TO TRACK WEST-SOUTHWESTWARD TO SOUTHWESTWARD
AFTER TAU 120. DUE TO THE LARGE SPREAD IN THE MODEL SOLUTIONS, THERE
IS LOW CONFIDENCE IN THE OFFICIAL JTWC FORECAST.//
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