WDPN31 PGTW 180300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 
23//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 15W (MEGI), LOCATED APPROXIMATELY 130 NM NORTH-
NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WEST-SOUTHWESTWARD AT 
13 KNOTS OVER THE PAST 06 HOURS. THOUGH STRIPPED OF ITS SUPER 
TYPHOON STATUS WHILE TRANSITING THE HIGH PEAKS OF THE SIERRA MADRE 
AFTER MAKING LANDFALL AROUND 0330Z, MEGI REMAINS A FORMIDABLE 
TROPICAL CYCLONE. THE DEEPEST CENTRAL CONVECTION HAS WEAKENED AND 
BECOME FRAGMENTED DUE TO CONTINUED LAND INTERACTION. HOWEVER, MEGI 
IS POSITIONED TO ENTER BACK OVER FAVORABLE WATERS WITHIN THE NEXT 
FEW HOURS AND RE-INTENSIFY. POLEWARD OUTFLOW REMAINS ROBUST AND 
VERTICAL WIND SHEAR IS LOW. THE INITIAL INTENSITY FOR THE PREVIOUS 
TWO FORECASTS HAS BEEN DIFFICULT TO ACCESS DUE TO A LACK OF 
OBSERVATIONAL DATA FROM THE PHILIPPINES AND UNREPRESENTATIVE DVORAK 
ESTIMATES. POSITION CONFIDENCE IS FAIR BASED ON SPIRAL BANDS RINGING 
THE CENTER PART OF THE CIRCULATION IN INFRARED SATELLITE IMAGERY. 
3. FORECAST REASONING.
   A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS 
PROGNOSTIC REASONING BULLETIN.
   B. ONCE MEGI MOVES INTO THE SOUTH CHINA SEA WITHIN THE NEXT FEW 
HOURS AN ADEQUATE INTENSITY ESTIMATE CAN BE DETERMINED WITH THE 
DVORAK METHOD. UNTIL THEN THE INTENSITY FORECAST IS HINGED ON AN 
INITIAL INTENSITY OF 95 KNOTS. NONETHELESS THE SYSTEM WILL LIKELY 
RAMP UP QUICKLY UNDER THE INFLUENCE OF HIGH SEA SURFACE 
TEMPERATURES, STRONG VORTICITY, LOW VERTICAL WIND SHEAR, AND A 
POLEWARD OUTFLOW MECHANISM. THE SYSTEM WILL TRACK DUE WEST FOR THE 
FIRST 24 HOURS, THEN TURN MORE NORTH OF WEST TOWARDS A (SHORT WAVE)
TROUGH-INDUCED BREAK IN THE STEERING RIDGE. GFS, WBAR, AND NOGAPS 
APPEAR TO EXCESSIVELY WEAKEN THE STEERING RIDGE AND STALL THE SYSTEM 
IN THE EASTERN SOUTH CHINA SEA FOR 1 TO 1.5 DAYS THEN PULL THE 
SYSTEM UNREALISTICALLY NORTH TO THE EAST OF HONG KONG. ECMWF WEAKENS 
THE RIDGE SIGNIFICANTLY LESS, CONSISTENT WITH THE MOSTLY ZONAL FLOW 
PROGGED IN THE MID-LATITUDES, AND BUILDS THE RIDGE BACK IN TO THE 
WEST AFTER THE TROUGH PASSES AROUND TAU 72. THIS FORECAST LIES ON 
THE ECMWF SIDE OF THE MODEL CONSENSUS, WHICH TO DATE HAS PERFORMED 
THE BEST AMONG THE CONSENSUS MEMBERS.
   C. THERE IS SIGNIFICANT SPREAD AMONG THE MODELS IN THE LATER 
FORECAST PERIOD. A SLIGHT INCREASE IN VERTICAL WIND SHEAR WILL 
LIKELY MODERATE INTENSIFICATION OR EVEN INCITE SLIGHT WEAKENING AS 
MEGI NEARS CHINA.//
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