Tropical Storm PRAPIROON Advisory mar, 09.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 22W (PRAPIROON) WARNING NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 22W (PRAPIROON), LOCATED APPROXIMATELY 585 NM SOUTH-
SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD AT 05
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS DEEP CONVECTIVE BANDS STEADILY WRAPPING TOWARDS
THE CENTER OF THE LOW LEVEL CIRCULATION CENTER (LLCC). APPARENT IN
THE MSI IS THE POSSIBLE BEGINNINGS OF AN EYE FEATURE, WHICH IS
SUPPORTED BY A 082301Z SSMIS 91H MICROWAVE PASS. THE CURRENT
POSITION IS BASED ON THE MSI LOOP AND IS SUPPORTED BY A PGTW FIX AND
THE SSMIS PASS. THE CURRENT INTENSITY IS BASED ON 4.0/4.0 DVORAK
ESTIMATES FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS INDICATES RADIAL
OUTFLOW ASSOCIATED WITH A POINT SOURCE ANTICYCLONE OVER THE LLCC
CONTINUES TO PROVIDE GOOD VENTILATION AND A LOW VERTICAL WIND SHEAR
(VWS) ENVIRONMENT (05 TO 10 KNOTS). TY 22W HAS SLOWED SLIGHTLY AND
HAS DRIFTED SOUTH BY ABOUT 0.2 DEGREES OVER THE PAST 12 HOURS, WHICH
INDICATES THE SUBTROPICAL RIDGE (STR) IS STARTING TO WEAKEN SLIGHTLY
AS THE SYSTEM BUILDS; BOTH OF WHICH ARE LIKELY CAUSING THE SLOWING
OBSERVED. THE SOUTHERLY DRIFT SUGGESTS THE APPROACHING MID-LATITUDE
TROUGH OVER THE YELLOW SEA HAS NOT MODIFIED THE STR ENOUGH TO ALLOW
THE SYSTEM TO BEGIN TRACKING NORTHWARD.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY PRAPIROON IS FORECAST TO CONTINUE ON A GENERAL WESTWARD
TRACK FOR THE NEXT 12 HOURS BUT WILL START MOVING MORE NORTHWARD AS
THE APPROACHING MID-LATITUDE TROUGH WEAKENS THE WESTERN EXTENT OF
THE STR AND A BUILDING NEAR EQUATORIAL RIDGE (NER) LINKS TO THE STR,
CAUSING TY 22W TO MOVE NORTHWESTWARD THROUGH TAU 36. FURTHER
MODIFICATION OF THE STR BY THE TROUGH AND NER WILL EVENTUALLY LEAD
TO A RECURVE TO THE NORTHEAST BETWEEN TAU 48 AND 72. FAVORABLE UPPER
LEVEL AND LOW LEVEL ENVIRONMENTS WILL ALLOW TY 22W TO INTENSIFY
THROUGH TAU 72.
   C. IN THE EXTENDED TAUS, TY 22W IS FORECAST TO TRACK
NORTHEASTWARD AS THE NER AMPLIFIES THE STR, CAUSING THE STR TO
REORIENT NORTHEAST TO SOUTHWEST. A SLIGHT DECREASE IN SEA SURFACE
TEMPERATURES AND INCREASING VWS WILL SLIGHTLY WEAKEN THE SYSTEM
BEYOND TAU 96. HOWEVER, THE ENVIRONMENT WILL REMAIN FAVORABLE FOR
THE SUSTAINMENT OF THE SYSTEM BEYOND THE FORECAST PERIOD. MODEL
GUIDANCE REMAINS CONSISTENT WITH A RECURVATURE SCENARIO, BUT STILL
HAS SIGNIFICANT TIMING/SPEED ISSUES TO RESOLVE. THE FORECAST FAVORS
ECMF AND GFS WITH A LATER TIMING ON THE RECURVATURE DUE TO NGPS,
WBAR, AND GFDN ALL SHOWING A SHARP TURN NORTHWARD AT THE INITIAL
POSITION. THOSE PARTICULAR MODELS HAVE BEEN INDICATING THIS TURN
OVER SEVERAL FORECAST CYCLES, THUS THE PREFERENCE FOR ECMF AND GFS.
THE CONFIDENCE IN THE FORECAST REMAINS LOW, BASED ON THE WIDE
VARIATION IN MODEL GUIDANCE.//
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