WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 22W (PRAPIROON), LOCATED APPROXIMATELY 585 NM SOUTH-
SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD AT 05 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS DEEP CONVECTIVE BANDS STEADILY WRAPPING TOWARDS 
THE CENTER OF THE LOW LEVEL CIRCULATION CENTER (LLCC). APPARENT IN 
THE MSI IS THE POSSIBLE BEGINNINGS OF AN EYE FEATURE, WHICH IS 
SUPPORTED BY A 082301Z SSMIS 91H MICROWAVE PASS. THE CURRENT 
POSITION IS BASED ON THE MSI LOOP AND IS SUPPORTED BY A PGTW FIX AND 
THE SSMIS PASS. THE CURRENT INTENSITY IS BASED ON 4.0/4.0 DVORAK 
ESTIMATES FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS INDICATES RADIAL 
OUTFLOW ASSOCIATED WITH A POINT SOURCE ANTICYCLONE OVER THE LLCC 
CONTINUES TO PROVIDE GOOD VENTILATION AND A LOW VERTICAL WIND SHEAR 
(VWS) ENVIRONMENT (05 TO 10 KNOTS). TY 22W HAS SLOWED SLIGHTLY AND 
HAS DRIFTED SOUTH BY ABOUT 0.2 DEGREES OVER THE PAST 12 HOURS, WHICH 
INDICATES THE SUBTROPICAL RIDGE (STR) IS STARTING TO WEAKEN SLIGHTLY 
AS THE SYSTEM BUILDS; BOTH OF WHICH ARE LIKELY CAUSING THE SLOWING 
OBSERVED. THE SOUTHERLY DRIFT SUGGESTS THE APPROACHING MID-LATITUDE 
TROUGH OVER THE YELLOW SEA HAS NOT MODIFIED THE STR ENOUGH TO ALLOW 
THE SYSTEM TO BEGIN TRACKING NORTHWARD. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY PRAPIROON IS FORECAST TO CONTINUE ON A GENERAL WESTWARD 
TRACK FOR THE NEXT 12 HOURS BUT WILL START MOVING MORE NORTHWARD AS 
THE APPROACHING MID-LATITUDE TROUGH WEAKENS THE WESTERN EXTENT OF 
THE STR AND A BUILDING NEAR EQUATORIAL RIDGE (NER) LINKS TO THE STR, 
CAUSING TY 22W TO MOVE NORTHWESTWARD THROUGH TAU 36. FURTHER 
MODIFICATION OF THE STR BY THE TROUGH AND NER WILL EVENTUALLY LEAD 
TO A RECURVE TO THE NORTHEAST BETWEEN TAU 48 AND 72. FAVORABLE UPPER 
LEVEL AND LOW LEVEL ENVIRONMENTS WILL ALLOW TY 22W TO INTENSIFY 
THROUGH TAU 72. 
   C. IN THE EXTENDED TAUS, TY 22W IS FORECAST TO TRACK 
NORTHEASTWARD AS THE NER AMPLIFIES THE STR, CAUSING THE STR TO 
REORIENT NORTHEAST TO SOUTHWEST. A SLIGHT DECREASE IN SEA SURFACE 
TEMPERATURES AND INCREASING VWS WILL SLIGHTLY WEAKEN THE SYSTEM 
BEYOND TAU 96. HOWEVER, THE ENVIRONMENT WILL REMAIN FAVORABLE FOR 
THE SUSTAINMENT OF THE SYSTEM BEYOND THE FORECAST PERIOD. MODEL 
GUIDANCE REMAINS CONSISTENT WITH A RECURVATURE SCENARIO, BUT STILL 
HAS SIGNIFICANT TIMING/SPEED ISSUES TO RESOLVE. THE FORECAST FAVORS 
ECMF AND GFS WITH A LATER TIMING ON THE RECURVATURE DUE TO NGPS, 
WBAR, AND GFDN ALL SHOWING A SHARP TURN NORTHWARD AT THE INITIAL 
POSITION. THOSE PARTICULAR MODELS HAVE BEEN INDICATING THIS TURN 
OVER SEVERAL FORECAST CYCLES, THUS THE PREFERENCE FOR ECMF AND GFS. 
THE CONFIDENCE IN THE FORECAST REMAINS LOW, BASED ON THE WIDE 
VARIATION IN MODEL GUIDANCE.//
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