WDPN31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.6N 142.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 434 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY DEPICTS A
WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC), WITH BANDS OF
SHALLOW CONVECTION WRAPPING INTO A SMALL CENTER. THE SYSTEM HAS
BEEN WOBBLING AROUND RATHER AIMLESSLY INSIDE THE WEAK STEERING
PATTERN AND REMAINED FOR THE MOST PART QUASI-STATIONARY OVER THE
PAST SIX HOURS. THIS HAS INDUCED SIGNIFICANT OCEANIC UPWELLING,
REDUCING SSTS UNDER THE SYSTEM, DEPRIVING IT OF ENERGY. A 291048Z
ASCAT-B PASS REVEALED A FAIRLY SYMMETRICAL WIND FIELD, WITH
GALE-FORCE WINDS PRESENT AROUND MOST OF THE LLCC, WITH SOME 45 KNOT
WINDS IN THE NORTHEAST QUADRANT. THE ULTRA-HIGH RESOLUTION (UHR)
VERSION OF THE SCATTEROMETER PASS REVEALED SOME 50 KNOT WINDS TO
THE NORTHEAST. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED CENTER IN THE PROXYVIS IMAGERY
AND THE SCATTEROMETER DATA. THE INITIAL INTENSITY IS ALSO ASSESSED
WITH HIGH CONFIDENCE BASED ON THE SCATTEROMETER DATA. ENVIRONMENTAL
CONDITIONS ARE MARGINAL, WITH LOW VWS OFFSET BY OCEANIC UPWELLING
AND THE PRESENCE OF THE AN UPPER-LEVEL CYCLONE OVER TOP OF THE
SYSTEM, LIMITING AVAILABLE OUTFLOW ALOFT, AS WELL AS DRY AIR
INTRUSION INTO THE CORE OF THE SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK AND COMPETING STEERING PATTERN,
WITH A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE
SOUTHEAST, AND ANOTHER STR CENTERED OVER CENTRAL HONSHU. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 34 KTS AT 291130Z
   CIMSS AIDT: 37 KTS AT 291130Z
   CIMSS D-PRINT: 38 KTS AT 291300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EASTWARD
   OTHER FACTORS: SIGNIFICANT OCEANIC UPWELLING AND DRY AIR
INTRUSION.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W WILL REMAIN STUCK
BETWEEN THE TWO RIDGES COMPETING FOR STEERING DOMINANCE AND IS
EXPECTED TO REMAIN QUASI-STATIONARY FOR THE NEXT 24 HOURS. AFTER
TAU 24, THE SYSTEM SHOULD BEGIN TO MOVE NORTHWARD A BIT AS THE STR
CURRENTLY TO THE SOUTHEAST SHIFTS NORTHWARD A BIT AND GIVES IT ONE
LAST PUSH. THE LATEST RUNS OF BOTH THE ECMWF AND GFS HAVE BACKED
OFF ON THE STRENGTH OF THE RIDGING OVER JAPAN, WHILE AT THE SAME
TIME BUILDING THE STR TO THE EAST AND EXPANDING IT NORTHWARD, WITH
THE GFS BEING THE MOST AGGRESSIVE IN DOING THIS. HENCE, AFTER TAU
36, TS 12W IS FORECAST TO MOVE QUICKLY OUT OF ITS QUASI-STATIONARY
AREA AND TRACK TOWARDS THE NORTHWEST ALONG THE SOUTHWESTERN SIDE OF
THIS BUILDING RIDGE TO THE EAST. THE QUESTION REMAINS, HOW STRONG
WILL THE RIDGE GET AND HOW FAR WEST WILL TS 12W TRACK. THE GFS
SHOWS THE STRONGEST TURN WEST-NORTHWEST, WHILE THE ECMWF INDICATES
A MORE NORTHWEST TRACK. BY TAU 72, THE SYSTEM REACHES AN INFLECTION
POINT, WITH ALL OF THE TRACK GUIDANCE INDICATING IT WILL TAKE A
SHARP RIGHT TURN, TOWARDS THE NORTHEAST, AFTER THIS TIME AS THE
RIDGE TO THE EAST SLIDES SOUTHWEST AND TS 12W ROUNDS THE RIDGE AXIS
WHILE AT THE SAME TIME BEING PICKED UP BY A MINOR SHORTWAVE TROF
OVER JAPAN. THE QUESTION AGAIN IS WHERE THIS TURN WILL OCCUR. THE
GFS DEPICTS THE FURTHEST SOUTHWEST STARTING POINT AND THE SHARPEST
TURN, KEEPING THE SYSTEM WELL OFFSHORE. THE ECMWF MEANWHILE MAKES
IT CLOSER TO HONSHU, OR EVEN MAKING LANDFALL BRIEFLY, BEFORE MAKING
A SHALLOWER TURN NORTHEASTWARD. REGARDLESS OF THE STARTING POINT,
BY TAU 120, THE SYSTEM WILL BE RACING OFF THE NORTHEAST INTO THE
OPEN WESTERN PACIFIC ALONG THE TIGHT GRADIENT ON THE NORTHWEST SIDE
OF THE STR TO THE SOUTHEAST.  IN TERMS OF INTENSITY, THE SYSTEM IS
FORECAST TO WEAKEN AS IT REMAINS QUASI-STATIONARY AND SUFFERS UNDER
PERSISTENT DRY AIR INTRUSION AND OCEANIC UPWELLING. BY TAU 48, AS
THE SYSTEM MOVES AWAY FROM ITS CURRENT POSITION, SSTS WILL INCREASE
SHARPLY, AND DEVELOPMENT OF A TUTT-CELL TO THE WEST WILL ENHANCE
UPPER-LEVEL OUTFLOW, ALLOWING THE SYSTEM TO INTENSIFY AS IT
APPROACHES HONSHU. THE SYSTEM WILL RAPIDLY WEAKEN AFTER TAU 96 DUE
TO DECREASING SSTS AND STEADILY INCREASING SHEAR.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERAL
AGREEMENT ON THE OVERALL TRACK SCENARIO, BUT DIFFERS SIGNIFICANTLY
IN BOTH THE TIMING AND STRENGTH OF THE TURN TOWARDS THE NORTHWEST,
AS WELL AS THE TURN BACK TO THE NORTHEAST AFTER TAU 72. AS
MENTIONED ABOVE, THE GFS MARKS THE WESTERN-MOST OUTLIER, REACHING A
POSITION ALMOST SOUTH OF KYOTO BEFORE TURNING BACK TO THE NORTHEAST
AND SHIFTING TO THE SOUTH EDGE OF THE GUIDANCE ENVELOPE BY TAU 120.
THE ECMWF MARKS THE EASTERN EDGE OF THE GUIDANCE PACKAGE THROUGH
TUA 72, THEN TRACKS STRAIGHT INTO HONSHU, MAKING LANDFALL EAST OF
TOKYO, BEFORE TURNING NORTHEASTWARD. THE REMAINDER OF THE GUIDANCE
IS ROUGHLY EVENLY SPREAD BETWEEN THE TWO OUTLIERS. THE JTWC
FORECAST IS PLACED EAST OF THE CONSENSUS MEAN, HEDGED TOWARDS THE
ECMWF, THROUGH TAU 72, THEN SHIFTS TO THE NORTH OF THE MEAN AND
CLOSE TO THE EC-AIFS TRACK THROUGH THE REMAINDER OF THE FORECAST.
ENSEMBLE GUIDANCE CONTINUES TO SHOW A LARGE AMOUNT OF UNCERTAINTY,
WITH INDIVIDUAL MEMBERS SHOWING POTENTIAL TRACKS EITHER DUE WEST
THROUGH NORTHEAST. HOWEVER, THE ENSEMBLE MEANS OF BOTH THE GEFS AND
ECENS KEEP THE SYSTEM OFFSHORE OF HONSHU AS THEY REACH THE
INFLECTION POINT AROUND TAU 72 AND SHIFT SHARPLY NORTHEAST.
INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH ALL AVAILABLE
GUIDANCE KEEPING THE PEAK INTENSITY BELOW 65 KNOTS THROUGHOUT THE
FORECAST PERIOD. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72 - 120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72 - 120 HR: MEDIUM//
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