WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 
21//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 22W (PRAPIROON), LOCATED APPROXIMATELY 370 NM SOUTH 
OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED EAST-NORTHEASTWARD 
AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY (EIR) AND A 121120Z SSMIS 91 GHZ MICROWAVE IMAGE 
DEPICT A LARGE WELL-DEFINED SYSTEM WITH A RAGGED EYE. THE INITIAL 
INTENSITY OF 90 KNOTS IS SLIGHTLY LOWER THAN AN AVERAGE OF DVORAK 
CURRENT INTENSITY ESTIMATES RANGING FROM 90 TO 102 KNOTS FROM PGTW 
AND RJTD DUE TO WARMING CLOUD TOPS SEEN IN THE EIR, INDICATIVE OF A 
SLIGHT WEAKENING TREND. THERE IS HIGH CONFIDENCE IN THE INITIAL 
POSITION BASED ON THE EYE FEATURE IN THE EIR AND SSMIS IMAGERY. 
UPPER-LEVEL ANALYSIS AND ANIMATED WATER VAPOR IMAGERY INDICATE 22W 
CONTINUES TO BE LOCATED BENEATH A POINT SOURCE ANTICYCLONE IN AN 
AREA OF LOW (05 TO 10 KNOT) VERTICAL WIND SHEAR (VWS) WITH GOOD 
RADIAL OUTFLOW. TY 22W IS CURRENTLY TRACKING SLOWLY EAST-
NORTHEASTWARD UNDER THE INFLUENCE OF A WEAK NEAR EQUATORIAL RIDGE 
(NER) TO THE SOUTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 22W IS EXPECTED TO CONTINUE TRACKING SLOWLY NORTHEASTWARD 
DURING THE NEXT 72 HOURS AS THE SYSTEM STEERS ALONG THE 
NORTHWESTERN PERIPHERY OF THE NER TO THE SOUTHEAST. AFTER TAU 72, A 
BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST OF TY 22W WILL BECOME 
THE DOMINANT STEERING INFLUENCE GIVING A MORE SLIGHTLY MORE 
NORTHERN COMPONENT. DYNAMIC MODEL GUIDANCE CONTINUES TO BE IN GOOD 
AGREEMENT THROUGH TAU 48, WITH THE EXCEPTION OF EGRR AND JGSM WHICH 
BOTH CONTINUE TO TAKE A MUCH SLOWER AND ERRATIC TRACK. BY TAU 72, 
MODELS SPREAD CONSIDERABLY AS THE STEERING INFLUENCE TRANSITIONS TO 
THE STR. DESPITE THE RECENT WEAKENING TREND, TY 22W IS EXPECTED TO 
INTENSIFY SLIGHTLY DURING THE NEXT 24 HOURS IN A FAVORABLE 
ENVIRONMENT. OCEAN HEAT CONTENT DECREASES NEAR 22 DEGREES NORTH 
WHICH WILL BEGIN TO SLOWLY WEAKEN TY 22W AS IT GAINS LATITUDE. 
CONFIDENCE IS HIGH IN THE JTWC TRACK FORECASTS THROUGH TAU 72.
   C. AFTER TAU 72, TY 22W IS EXPECTED TO TURN SLIGHTLY MORE 
NORTHWARD AS THE STR TO THE EAST BUILDS WESTWARD AND REORIENTS. THE 
WESTWARD EXTENSION OF THE STR WILL BE FAIRLY SHORT-LIVED AS A MID-
LATITUDE TROUGH DIGS IN EAST OF JAPAN. NEAR TAU 120 TY 22W IS 
EXPECTED TO SLOWLY TAKE  A MORE NORTHEASTWARD TRACK AS THE STR 
REORIENTS IN RESPONSE TO THE TROUGH. DYNAMIC MODEL GUIDANCE 
CONTINUES TO SPREAD AFTER TAU 72, WITH A DISAGREEMENT AMONGST 
MODELS IN THE SPEED  AND HOW MUCH OF A WESTWARD COMPONENT THE 
BUILDING STR WILL PROVIDE TO THE MORE NORTHERN TRACK, BUT THE 
SPREAD IS LESS THAN PREVIOUS RUNS. AFTER TAU 120, MODELS INDICATE 
TY 22W WILL RESUME ITS NORTHEAST TRACK AND ACCELERATE CONSIDERABLY 
BETWEEN THE STR AND THE PREVIOUSLY MENTIONED MID-LATITUDE TROUGH. 
GRADUAL WEAKENING THROUGH TAU 120 AS TY 22W SLOWLY TRACKS NORTH IN 
A LESS FAVORABLE ENVIRONMENT. FORECAST CONFIDENCE IS IMPROVING DUE 
TO LESS SPREAD IN THE MODELS BUT REMAINS LOW AFTER TAU 72 DUE TO 
HIGH VARIANCE IN TRACK SPEEDS AND DIRECTION.//
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