WDPN31 PGTW 250300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NESAT) WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 20W (NESAT), LOCATED APPROXIMATELY 560 NM EAST OF 
MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST 
SIX HOURS.  ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS SURGING 
CONVECTION AND TIGHTER SYSTEM ORGANIZATION DURING THE PAST SIX 
HOURS. TY 20W DOES NOT SHOW AN EYE YET, BUT A 242003Z SSMI IMAGE 
SHOWS A MICROWAVE EYE AND A 242353Z SSMIS SERIES SHOWS TIGHTLY 
CURVED BANDING WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC) 
IN ALL QUADRANTS. ANIMATED INFRARED IMAGERY SHOWS THE AREA OF COLD 
CLOUD TOPS EXPANDING AND SPREADING OUTWARDS FROM THE STORM. DVORAK 
INTENSITY ESTIMATES HAVE INCREASED TO 65 KNOTS FROM PGTW AND KNES, 
AND 55 KNOTS FROM RJTD. SATELLITE ANIMATION ALSO CONFIRMS THAT TY 
20W IS TRACKING JUST TO THE SOUTH OF WEST AS THE SUBTROPICAL RIDGE 
BUILDS OVER THE NORTHERN PHILIPPINE SEA. THE 241200Z PGTW UPPER 
LEVEL STREAMLINE ANALYSIS DEPICTS AN ANTICYCLONE EAST OF THE LLCC 
AND A DIFFLUENT ASYMPTOTE OVER THE TOP OF THE SYSTEM. TY 20W EXISTS 
IN A HIGHLY DIFFLUENT REGION WITH ONLY 5 TO 10 KNOTS OF VERTICAL 
WIND SHEAR OVER THE SYSTEM. SEA SURFACE TEMPERATURES ARE 30 DEGREES 
AND INCREASING SLIGHTLY ALONG TRACK. ANIMATED WATER VAPOR IMAGERY 
SHOWS UNIMPEDED OUTFLOW IN ALL QUADRANTS. A BROAD EQUATORWARD 
CHANNEL IS VENTING ALL THE WAY INTO THE SOUTHERN HEMISPHERE. 
3. FORECAST REASONING.
   A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS 
PROGNOSTIC REASONING BULLETIN.
   B. TY 20W WILL SUSTAIN A TRACK ALONG THE EXTREME SOUTHWESTERN 
PERIMETER OF THE SUBTROPICAL RIDGE UNTIL IT MAKES LANDFALL OVER 
LUZON. THE INFLUENCE OF THE RIDGE WILL WEAKEN SLIGHTLY AFTER TAU 12, 
ALLOWING MORE POLEWARD MOVEMENT. TY 20W IS ENTERING THE FERTILE 
GROUNDS OF THE PHILIPPINE SEA AND SHOWING SIGNS OF RAPID 
INTENSIFICATION. THE STORM HAS ATTAINED EXCELLENT OUTFLOW CONDITIONS 
THAT WILL ALLOW UNIMPEDED DEVELOPMENT UNTIL LAND INTERACTION 
PROVIDES A WEAKENING EFFECT.  THE INTENSITY RAMP-UP OVER THE NEXT 24 
HOURS IS A LITTLE MORE THAN ONE DVORAK VALUE PER DAY, WHICH IS NOT 
AGGRESSIVE CONSIDERING THE CURRENT SYNOPTIC SITUATION. TY 20W WILL 
ENCOUNTER EVEN WARMER SEA WATER OFF THE NORTHEAST COAST OF LUZON 
WHILE REMAINING IN A LOW SHEAR ENVIRONMENT AND NEAR TAU 42, IT WILL 
PEAK AT SUPER TYPHOON INTENSITY. THE LATEST GUIDANCE INDICATES THE 
ENTRY POINT WILL BE BETWEEN AUBAREDE POINT AND CASIGURAN. ONCE 
INLAND, TOPOGRAPHY WILL FORCE THE TRACK A LITTLE MORE WESTWARD AND 
DRIVE THE STORM ACROSS THE RUGGED TERRAIN OF THE SIERRA MADRES. 
RECENT GUIDANCE HAS COME A LITTLE SOUTH REGARDING BOTH ENTRY AND 
EXIT POINTS, BUT SUCH UNCERTAINTY IS TO BE EXPECTED UNTIL THE TIME 
TO LANDFALL SHORTENS. EACH SUCCESSIVE FIX WILL RESULT IN BETTER 
FOCUS ON THE TRACK FORECAST. DESPITE THE SLIDE TO THE SOUTH, 
HOWEVER, TIME OVER LAND STILL WORKS OUT TO ROUGHLY 15 HOURS.  
ACCORDING TO STATISTICAL ANALOGUES, A 15 HOUR OVER-LAND TRACK 
RESULTS IN A FORTY PER CENT REDUCTION IN STORM INTENSITY, WHICH 
WOULD RESULT IN TY NESAT EJECTING INTO THE SOUTH CHINA SEA (SCS) AT 
80 KNOTS. ONCE IN THE SCS, TY 20W WILL BE OVER WARM WATERS BUT IN A 
HIGHER SHEAR ENVIRONMENT, AND THUS UNDERGO ONLY MODERATE RE-
INTENSIFICATION.
    C. THE EXTENDED RANGE TRACK POINTS THE STORM CLOSE TOWARDS HONG 
KONG, BUT WITH EACH SUCCESSIVE RUN, GUIDANCE HAS SHIFTED SOUTH. THE 
MOST RECENT TRACK POINTS TO LANDFALL BETWEEN HONG KONG AND HAINAN, 
WITH THE STORM STILL AT TYPHOON STRENGTH. WHILE INTENSITY GUIDANCE 
IS STILL NOT KEEPING UP WITH THE STORM'S ACTUAL DEVELOPMENT, TRACK 
GUIDANCE HAS BEEN IN EXCELLENT AGREEMENT ON THE OVERALL SCENARIO. 
THE TRACK FORECAST STAYS CLOSE TO AND SLIGHTLY FASTER THAN 
CONSENSUS, WHILE THE INTENSITY FORECAST IS BASED ON OBSERVED 
ENVIRONMENTAL CONDITIONS FACTORED WITH A RAPID INTENSIFICATION 
SCENARIO, WHICH IS TYPICAL OF A SYSTEM OF THIS TYPE, TRACK, AND 
SEASON.//
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