Tropical Storm PRAPIROON Advisory Pzt, 08.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON)
WARNING NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY
680NM SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD
AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR)
SATELLITE IMAGERY DEPICTS A RAPIDLY CONSOLIDATING SYSTEM WITH
IMPROVED DEEP CONVECTIVE BANDING WRAPPING FROM THE SOUTHWEST
QUADRANT INTO THE EAST QUADRANT OF THE LOW-LEVEL CIRCULATION CENTER
(LLCC). IR IMAGERY ALSO SHOWS A WEAK CONVECTIVE BAND OVER THE
NORTHEAST QUADRANT. A 071715Z TRMM 37GHZ IMAGE ALSO DEPICTS TIGHTLY-
CURVED BANDING AND A WELL-DEFINED LLCC, THEREFORE, THERE IS GOOD
CONFIDENCE IN THE CURRENT POSITION AND RECENT MOTION WESTWARD. THE
INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON DVORAK ESTIMATES
OF 35 KNOTS FROM PGTW AND RJTD AND IS CONSISTENT WITH BOTH STRUCTURE
AND AUTOMATED DVORAK ESTIMATES. ANIMATED WATER VAPOR IMAGERY
SHOWS IMPROVING POLEWARD OUTFLOW OVER THE NORTHERN SEMI-CIRCLE
ENHANCED BY A TUTT CELL NEAR 26N 148E. THE 07/12Z 500MB ANALYSIS
DEPICTS A BROAD LONG-WAVE TROUGH OVER ASIA WITH A MAJOR SHORTWAVE
TROUGH NEAR 90E AND ANOTHER TROUGH CURRENTLY TRACKING OVER EASTERN
JAPAN. ADDITIONALLY, THE 200MB ANALYSIS SHOWS A STRONG POLAR JET
OVER CENTRAL ASIA EXTENDING EASTWARD OVER SOUTH KOREA AND CENTRAL
HONSHU WITH MODERATE WESTERLY FLOW AS FAR SOUTH AS THE RYUKYUS;
UPPER-AIR DATA AT MINAMIDAITO-JIMA INDICATES UPPER-LEVEL WESTERLY
WINDS AT 20-25 KNOTS WHILE NAZE SHOWS 40-50 KNOTS. THESE SYNOPTIC
FEATURES ARE IMPORTANT FACTORS IN, AND SUPPORT, THE JTWC FORECAST
PHILOSOPHY.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. AS THE TROUGH CURRENTLY LOCATED OVER EASTERN JAPAN PROPAGATES
EASTWARD, THE SUBTROPICAL RIDGE (STR) IS FORECAST TO RE-BUILD
BRIEFLY ALLOWING TS 22W TO CONTINUE TRACKING WESTWARD AT 06-08 KNOTS
(CLIMATOLOGICALLY SLOW SPEEDS) THROUGH TAU 36. AFTER TAU 36, THE STR
WILL GRADUALLY ERODE AS A MAJOR SHORTWAVE TROUGH (NEAR 90E NOW) DIGS
INTO THE EAST CHINA SEA AROUND TAU 48 AND TS 22W WILL SLOW TO 02-04
KNOTS. DYNAMIC MODEL GUIDANCE IS CONSISTENT IN DEPICTING THE
SYNOPTIC SITUATION; HOWEVER, THE MODELS DIFFER ON THE EXACT TRACK.
THERE ARE ESSENTIALLY TWO CLUSTERS OF SOLUTIONS: NOGAPS AND WBAR
SHOW A VERY ABRUPT, UNREALISTIC CLOCKWISE LOOP AROUND 135-137E AND
LIKELY ARE OVER-REACTING TO THE TROUGH/WESTERLIES TO THE NORTH. THE
REMAINDER OF THE GUIDANCE (JGSM, ECMWF, GFS AND EGRR) IS MORE
REALISTIC AND DEPICTS A SLOW WESTWARD TO WEST-NORTHWESTWARD TRACK
THROUGH TAU 72. THE JTWC FORECAST FAVORS THE LATTER GROUP AND IS
POSITIONED EQUATORWARD OF THE MULTI-MODEL CONSENSUS TO OFFSET NOGAPS
AND WBAR. GFDN CONTINUES TO HANDLE THE INTENSITY POORLY AND IS
TRUNCATED AT TAU 24. TS 22W IS FORECAST TO INTENSIFY TO 85 KNOTS BY
TAU 72 UNDER IMPROVING UPPER-LEVEL CONDITIONS.
   C. IN THE EXTENDED TAUS, TS 22W IS FORECAST TO TURN WEST-
NORTHWESTWARD TO NORTHWESTWARD AND TO SLOW SIGNIFICANTLY. THERE IS
SOME POTENTIAL FOR THE SYSTEM TO LOOP OR BECOME QUASI-STATIONARY AS
WELL. THIS MOTION IS DUE TO THE PERSISTENT, STRONG (AND ZONAL)
WESTERLY FLOW EXPECTED TO MAINTAIN OVER KOREA AND JAPAN AS WELL AS
THE LACK OF A DEEP, DYNAMIC TROUGH AFTER TAU 96. TS 22W WILL LIKELY
RE-CURVE SLOWLY UNTIL IT TRACKS NORTH OF 28-30N. FORTUNATELY, DUE TO
THE STRONG WESTERLY FLOW, THE SYSTEM IS UNLIKELY TO AFFECT KOREA AND
JAPAN WITH THE EXCEPTION OF OKINAWA. AFTER TAU 120, THE MAJORITY OF
THE DYNAMIC MODELS INDICATE INCREASED EAST-NORTHEASTERLY WINDS (GALE-
FORCE) OVER OKINAWA DUE TO AN ENHANCED GRADIENT BETWEEN TS 22W AND
AN EAST-WEST ORIENTED FRONTAL SYSTEM. A DIRECT HIT ON OKINAWA
APPEARS UNLIKELY AT THIS POINT. TS 22W IS FORECAST TO CONTINUE
INTENSIFYING AND WILL PEAK AT 105 KNOTS AND POSSIBLY HIGHER DUE TO
IMPROVING POLEWARD OUTFLOW; VERTICAL WIND SHEAR IS ALSO EXPECTED TO
REMAIN FAVORABLE DUE, AGAIN, TO THE LACK OF A DEEP SHORTWAVE TROUGH.
OVERALL, THERE IS LOW CONFIDENCE IN THE EXACT FORECAST TRACK DUE TO
THE WEAK STEERING INFLUENCE AFTER TAU 48. HOWEVER, IT IS IMPORTANT
TO EMPHASIZE THAT THE MODELS ARE VERY CONSISTENT IN DEPICTING THE
GENERAL SYNOPTIC PATTERN.//
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