Tropical Storm PRAPIROON Advisory Cts, 13.10.

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.//
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