WDPN31 PGTW 150300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (MEGI) WARNING NR 09// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TYPHOON 15W (MEGI), LOCATED APPROXIMATELY 940 NM EAST- SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTI-SPECTRAL IMAGERY, AIRCRAFT DROPSONDES, AND MICROWAVE SOUNDINGS ALL CONFIRM SUBSTANTIAL INTENSIFICATION DURING THE PAST 12 HOURS, ALTHOUGH THE RATE OF DEEPENING HAS SLOWED SLIGHTLY DURING THE PAST THREE HOURS WITH INFRARED READINGS OF THE CENTRAL DENSE OVERCAST (CDO) SHOWING TEMPERATURES BELOW NEGATIVE 80 CELSIUS. A 142112Z 37GHZ SSMI-S MICROWAVE IMAGE SHOWS A WELL-DEFINED EYE. CONFIDENCE IN THE CURRENT POSITION IS BOLSTERED BY AIRCRAFT RECONNAISSANCE DATA. THE CURRENT INTENSITY IS BASED ON AIRCRAFT OBSERVATIONS FROM VARIOUS POINTS WITHIN THE STORM AS WELL AS A DVORAK ESTIMATE OF 90 KNOTS FROM PGTW. WATER VAPOR ANIMATION SHOWS VIGOROUS POLEWARD AND EQUATORWARD OUTFLOW CHANNELS HAVE DEVELOPED. SOME SUBSIDENCE ASSOCIATED WITH A TUTT CELL REMAINS JUST EAST OF THE VISAYAS, BUT IN THE NEAR TERM MEGI'S TRACK EXISTS IN A REGION OF VERY FAVORABLE CONDITIONS FOR FURTHER INTENSIFICATION. 3. FORECAST REASONING. A. THE FORECAST PHILOSOPHY REMAINS UNCHANGED. B. TS 15W IS CURRENTLY TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE MID-LEVEL SUBTROPICAL RIDGE (STR). THERE IS A WEAKNESS IN THE STR ALONG THE 130TH MERIDIAN THAT IS TEMPORARILY INDUCING SOME POLEWARD TRAJECTORY IN THE TRACK BUT THAT WEAKNESS IS EXPECTED TO FILL AS A MAJOR SHORT-WAVE TROUGH CURRENTLY TRACKING OVER THE EAST CHINA SEA PASSES DOWNSTREAM, ALLOWING THE STR RE-BUILD. THE BUILDING RIDGE IS THEN EXPECTED TO DRIVE THE STORM TO THE WEST-SOUTHWEST TOWARDS NORTHERN LUZON. MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH THAT SCENARIO THROUGH TAU 48, THEN NOGAPS AND GFDN SUSTAIN THE WEST- NORTHWEST TRACK, POINTING THE STORM AT TAIWAN, WHILE ECMWF, EGRR, AND THE JTWC CONSENSUS MODEL STEER THE STORM WESTWARD TOWARD NORTHERN LUZON. BECAUSE THE GFDN TRACKER IS NESTED IN NOGAPS, THE OPERATIVE ASSUMPTION IS THAT NOGAPS IS CAUSING THE GFDN SOLUTION TO SHIFT POLEWARD. THE CURRENT TRACK FORECAST IS BASED ON THE SOUTHERN SOLUTION DUE TO A LACK OF MERIDIONAL FLOW ALOFT THAT WOULD BE NECESSARY TO WEAKEN THE RIDGE ENOUGH TO DRAW THE STORM POLEWARD. C. AFTER TAU 72, TY 15W IS FORECAST TO MAKE LANDFALL OVER LUZON AT OR NEAR SUPER TYPHOON STRENGTH. THE SYTEM SHOULD WEAKEN CONSIDERABLY WHILE CROSSING THE MOUNTAINOUS TERRAIN OF LUZON BUT IS EXPECTED TO MAINTAIN ENOUGH ENERGY TO RE-EMERGE INTO THE SOUTH CHINA SEA AT TYPHOON STRENGTH WITH A SLIGHT POLEWARD DEFLECTION.//