Tropical Storm PRAPIROON Advisory lun, 08-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (PRAPIROON)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 22W (PRAPIROON), LOCATED APPROXIMATELY
670NM SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WESTWARD
AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR)
SATELLITE IMAGERY DEPICTS A RAPIDLY CONSOLIDATING SYSTEM WITH
MULTIPLE DEEP CONVECTIVE BANDS WRAPPING INTO THE WELL-DEFINED LOW-
LEVEL CIRCULATION CENTER (LLCC). A 072313Z SSMIS 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 45 KNOTS BASED ON
DVORAK ESTIMATES OF 45 KNOTS FROM PGTW AND RJTD AND IS CONSISTENT
WITH RECENT UW-CIMSS AUTOMATED DVORAK ESTIMATES. ANIMATED WATER
VAPOR IMAGERY SHOWS NEAR-RADIAL OUTFLOW WITH IMPROVED POLEWARD
OUTFLOW OVER THE NORTHERN SEMI-CIRCLE ENHANCED BY A TUTT CELL NEAR
28N 150E. 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 03-05 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 02-03
KNOTS. DYNAMIC MODEL GUIDANCE IS CONSISTENT IN DEPICTING THE
MIDLATITUDE SYNOPTIC SITUATION; HOWEVER, THE MODELS ARE CURRENTLY IN
POOR AGREEMENT, DIVERGE SIGNIFICANTLY AFTER TAU 24, AND HAVE BEEN
HIGHLY ERRATIC OVER THE PAST 24 HOURS. THERE ARE ESSENTIALLY TWO
CLUSTERS OF SOLUTIONS: NOGAPS, GFDN AND WBAR SHOW A VERY ABRUPT
NORTHWARD TRACK AFTER 24 WHILE GFS, JGSM, EGRR AND ECMWF SHOW A
WESTWARD TRACK THROUGH TAU 48 THEN MORE GRADUAL, SLOWER
NORTHWESTWARD TURN THROUGH TAU 72. IT APPEARS THAT NOGAPS, GFDN AND
WBAR ARE LIKELY OVER-REACTING TO THE TROUGH/WESTERLIES TO THE NORTH.
THE JTWC FORECAST FAVORS THE ECMWF, JGSM, GFS AND EGRR GROUP AND IS
POSITIONED WEST OF THE MULTI-MODEL CONSENSUS TO OFFSET NOGAPS, GFDN
AND WBAR. TS 22W IS FORECAST TO INTENSIFY TO 95 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. MODEL GUIDANCE IN THE EXTENDED
TAUS CONTINUES TO BE IN POOR AGREEMENT. IN PARTICULAR, GFS AND
NOGAPS TRACK TS 22W QUICKLY EAST-NORTHEASTWARD UNDER THE STEERING
INFLUENCE OF A BUILDING NEAR-EQUATORIAL RIDGE (NER) TO THE SOUTH,
WHICH IS UNLIKELY. THEY ALSO TRACK THE SYSTEM INTO THE STR, WHICH
REMAINS POSITIONED TO THE NORTHEAST. THIS RE-CURVE SCENARIO IS NOT
ASSOCIATED WITH A TYPICAL RE-CURVE SCENARIO AROUND THE STR INTO THE
MIDLATITUDE WESTERLIES, WHICH REMAIN ZONAL NORTH OF 28N, BUT RATHER
IS DUE SOLELY TO THE NER. THE JTWC FORECAST CONTINUES TO FAVOR
ECMWF, EGRR AND JGSM IN THE EXTENDED TAUS. 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 AND
POOR MODEL AGREEMENT. HOWEVER, IT IS IMPORTANT TO EMPHASIZE THAT THE
MODELS ARE VERY CONSISTENT IN DEPICTING THE GENERAL MIDLATITUDE
SYNOPTIC PATTERN.//
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