MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 22// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 22W (PRAPIROON), LOCATED APPROXIMATELY 360 NM SOUTH- EAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED NORTHEASTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR) SATELLITE IMAGERY AND A 121120Z SSMIS 91 GHZ MICROWAVE IMAGE DEPICT A LARGE, WELL-DEFINED SYSTEM WITH TIGHTLY CURVED CONVECTIVE BANDING. BOTH THE IR AND MICROWAVE IMAGERY INDICATE A WEAKENING SYSTEM WITH DECREASED CONVECTION ALONG THE NORTHERN SEMICIRCLE. THE INITIAL INTENSITY OF 85 KNOTS IS BASED ON DVORAK CURRENT INTENSITY ESTIMATES RANGING FROM 77 TO 90 KNOTS FROM PGTW, KNES AND RJTD. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON AN EYE FEATURE IN THE AMSU-B IMAGERY. UPPER-LEVEL ANALYSIS INDICATES 22W IS LOCATED IN A REGION OF WEAK (5-10 KNOT) VERTICAL WIND SHEAR (VWS) SLIGHTLY WEST OF A POINT SOURCE ANTICYCLONE. ANIMATED WATER VAPOR IMAGERY SHOWS GOOD RADIAL OUTFLOW. HOWEVER, DECREASED CONVECTION ALONG THE NORTHERN PORTION OF OF THE SYSTEM IS EVIDENT. DUE TO THE SLOW MOVEMENT OF 22W DURING THE PAST 48 HOURS SEA SURFACE TEMPERATURES IN THE VICINITY OF THE SYSTEM HAVE SLIGHTLY DECREASED. THIS IS LIKELY A DRIVING FACTOR IN THE CURRENT DECREASE IN INTENSITY. TY 22W IS CURRENTLY TRACKING SLOWLY 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 48 HOURS AS THE SYSTEM STEERS ALONG THE NORTHWESTERN PERIPHERY OF THE NER TO THE SOUTHEAST. AFTER TAU 48, A BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST OF TY 22W WILL BECOME THE DOMINANT STEERING INFLUENCE, TRACKING THE SYSTEM ALONG A SLIGHTLY MORE NORTHWARD COMPONENT. DECREASING OCEAN HEAT CONTENT AND SEA SURFACE TEMPERATUES SHOULD ACT TO COUNTERACT THE FAVORABLE OUTFLOW AND WEAK TO MARGINAL VWS, RESULTING IN STEADY TO SLIGHTLY WEAKENING INTENSITIES DURING THE NEXT 72 HOURS. DYNAMIC MODEL GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT THROUGH TAU 48, WITH THE EXCEPTION OF EGRR AND JGSM WHICH HAVE BOTH TAKEN A MUCH SLOWER AND ERRATIC TRACK DURING THE PAST SEVERAL RUNS. BY TAU 72, MODELS BEGIN TO SPREAD BUT ARE MUCH CLOSER IN AGREEMENT THAN PREVIOUS RUNS. CONFIDENCE IS HIGH IN THE JTWC TRACK FORECAST THROUGH TAU 72. C. AFTER TAU 72, TY 22W IS EXPECTED TO CONTINUE TRACKING ALONG THE WESTERN PERIPHERY OF THE STR TO THE EAST WHILE GAINING FORWARD TRACK SPEED. THE WESTWARD EXTENSION OF THE STR WILL BE FAIRLY SHORT- LIVED AS A MID-LATITUDE TROUGH DIGS IN EAST OF JAPAN. AS THE STEERING RIDGE ERODES, TY 22W IS EXPECTED TO RESUME A MORE NORTHEASTWARD TRACK AROUND TAU 96. INTENSITY IS EXPECTED TO CONTINUE DECREASING AS SEA SURFACE TEMPERATURES DECREASE AND VWS INCREASES. BY TAU 96 TY 22W WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE AND COMPLETE EXTRATROPICAL TRANSITION BY TAU 120. DYNAMIC MODEL GUIDANCE CONTINUES TO SPREAD AFTER TAU 72, WITH DISCREPANCIES IN BOTH TRACK SPEED AND DIRECTION BASED ON THE INFLUENCE OF THE APPROACHING TROUGH. HOWEVER, THE SPREAD IN THE MODEL GUIDANCE HAS DECREASED DURING THE PAST SEVERAL RUNS. FORECAST CONFIDENCE CONTINUES TO IMPROVE DUE TO THE DECREASING SPREAD BUT REMAINS LOW AFTER TAU 72 DUE TO HIGH VARIANCE IN TRACK SPEEDS.// NNNN NNNN