Tropical Storm PRAPIROON Advisory vie, 12-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR
19//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 22W (PRAPIROON), LOCATED APPROXIMATELY 390 NM SOUTH
OF KADENA AIR BASE, OKINAWA, JAPAN, HAS MADE A TURN TO THE NORTHEAST
AND TRACKED AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) AND A 120006Z SSMIS 91GHZ
MICROWAVE IMAGE DEPICT A WELL-DEFINED SYSTEM WITH TIGHTLY WRAPPED
CONVECTIVE BANDING AND A RAGGED EYE. THE INITIAL INTENSITY IS BASED
ON DVORAK INTENSITY ESTIMATES OF 102 KNOTS FROM PGTW AND RJTD. THERE
IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON THE EYE FEATURE
IN THE MSI AND SSMIS IMAGERY. UPPER-LEVEL ANALYSIS AND ANIMATED
WATER VAPOR IMAGERY INDICATE 22W IS 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 HAS NOW TAKEN ON A MORE
NORTHEASTWARD TRACK 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. BETWEEN TAUS 48 AND 72 A
BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST OF TY PRAPIROON WILL
BECOME THE PREDOMINANT STEERING FEATURE. A NORTHERLY TURN IS
EXPECTED NEAR TAU 72 AS THIS STR BUILDS WESTWARD. WITH THE EXCEPTION
OF JGSM AND EGRR, THE SLOWEST AND LEFTMOST OUTLIERS, DYNAMIC MODEL
GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT THROUGH TAU 36. BY TAU
72, MODELS BEGIN TO SPREAD CONSIDERABLY AS THE STEERING REGIME
TRANSITIONS. TY 22W IS EXPECTED TO INTENSIFY SLIGHTLY DURING THE
NEXT 12 HOURS IN A FAVORABLE ENVIRONMENT. AS OCEAN HEAT CONTENT
BEGINS TO DECREASE NEAR 22 DEGREES NORTH INTENSITY IS EXPECTED TO
GRADUALLY DECREASE AFTER TAU 36. CONFIDENCE IS HIGH IN THE JTWC
TRACK AND INTENSITY FORECASTS UNTIL TAU 72, WITH NO SIGNIFICANT
CHANGES FROM THE PREVIOUS FORECAST.
   C. AFTER TAU 72, TY 22W IS EXPECTED TO TURN NORTHWARD AS THE STR
TO THE EAST BUILDS WESTWARD AND REORIENTS IN A MORE NORTH-SOUTH
DIRECTION. THE WESTWARD EXTENSION OF THE STR WILL BE FAIRLY SHORT-
LIVED AS A VIGOROUS MID-LATITUDE TROUGH EMERGES EAST OF JAPAN. NEAR
TAU 120 TY PRAPIROON IS EXPECTED TO SLOWLY TAKE ON A MORE EASTWARD
TRACK AS THE STR ERODES. BY TAU 120, DYNAMIC MODEL GUIDANCE IS
SPREAD UPWARDS OF 500NM, WITH EGRR TRACKING THE SYSTEM WESTWARD
AFTER TAU 72 AND WBAR INDICATING A CONTINUOUS NORTHEASTERLY TRACK.
MOST MODELS INDICATE A TURN TO THE NORTH AFTER TAU 72 IN RESPONSE TO
THE BUILDING STR TO THE EAST. GRADUAL WEAKENING IS EXPECTED AS TY
22W SLOWLY GAINS LATITUDE IN A LESS FAVORABLE ENVIRONMENT. FORECAST
CONFIDENCE AFTER TAU 72 REMAINS LOW DUE TO HIGH VARIANCE IN TRACK
SPEEDS AND DIRECTION.//
NNNN
NNNN