Tropical Storm PRAPIROON Advisory sab, 13.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR
23//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 22W (PRAPIROON), LOCATED APPROXIMATELY 350 NM SOUTH-
SOUTHEAST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED
NORTHEASTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED
(IR) SATELLITE IMAGERY AND A 122353Z SSMIS 91 GHZ MICROWAVE IMAGE
DEPICT A LARGE, WELL-DEFINED SYSTEM WITH TIGHTLY CURVED CONVECTIVE
BANDING. BOTH THE IR AND MICROWAVE IMAGERY CONTINUE TO INDICATE
SLIGHT WEAKENING WITH DECREASED CONVECTION ALONG THE NORTHWEST
QUADRANT. THE INITIAL INTENSITY OF 80 KNOTS IS BASED ON DVORAK
CURRENT INTENSITY ESTIMATES RANGING FROM 65 TO 90 KNOTS FROM PGTW,
KNES, AND RJTD. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION
BASED ON AN EYE FEATURE IN THE SSMIS 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,
WEAKENING IS EVIDENT AS CONVECTION HAS CONTINUED TO DECREASE
SLIGHTLY IN THE NORTHERN PORTION OF THE SYSTEM. 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 HAS LIKELY
CONTRIBUTED TO A DECREASE IN THE CURRENT 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 36 HOURS AS THE SYSTEM STEERS ALONG THE NORTHWESTERN
PERIPHERY OF THE NER TO THE SOUTHEAST. AFTER TAU 36, 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. AFTER TAU 48, 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. DECREASING OCEAN HEAT CONTENT AND SEA SURFACE
TEMPERATUES SHOULD COUNTERACT THE FAVORABLE OUTFLOW AND WEAK TO
MARGINAL VWS, RESULTING IN STEADY TO SLIGHTLY WEAKENING INTENSITIES
DURING THE NEXT 48 HOURS. AROUND TAU 72, INCREASED POLEWARD OUTFLOW
AHEAD OF THE APPROACHING TROUGH MAY RESULT IN A SLIGHT INCREASE IN
INTENSITY. 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 DAYS.
BY TAU 48, MODELS BEGIN TO SPREAD BUT ARE CLOSER IN AGREEMENT THAN
PREVIOUS RUNS. CONFIDENCE IS HIGH IN THE JTWC TRACK FORECAST THROUGH
TAU 48.
   C.  AS THE STEERING RIDGE ERODES AFTER TAU 72, TY 22W IS EXPECTED
TO RESUME A MORE NORTHEASTWARD TRACK AND SIGNIFICANTLY INCREASE IN
FORWARD SPEED. INTENSITY IS EXPECTED TO DECREASE 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 AS A VERY STRONG EXTRATROPICAL LOW. 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
CONTINUED TO 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