WDPN31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (KROVANH) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.8N 127.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 199 NM NORTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH
PERSISTENT CONVECTION DISPLACED TO THE EASTERN PERIPHERY. THE
CONVECTION IS BEING ENHANCED BY A STRONG POLEWARD OUTFLOW CHANNEL
ASSOCIATED WITH A 160-KT JET STREAK AHEAD OF A FAST-MOVING TROUGH
OVER THE SEA OF JAPAN. CONCURRENTLY, AN UPPER-LEVEL RIDGE IS
BUILDING IN BEHIND THE TROUGH, RESULTING IN MODERATE TO HIGH
NORTHWESTERLY VERTICAL WIND SHEAR (VWS). VERY DRY, COOL AIR FROM
THE YELLOW SEA IS ADVECTING SOUTHWARD AND INTO THE CIRCULATION. IN
COMBINATION WITH THE SHEAR, THIS DRY-AIR INTRUSION EXPLAINS THE
ABSENCE OF CONVECTION OVER THE WESTERN SEMICIRCLE. DESPITE THE
UNFAVORABLE ENVIRONMENT, RECENT SHIP OBSERVATIONS IN THE
NORTHWESTERN QUADRANT REPORTED WINDS OF 33 TO 42 KTS, AND A 040144Z
ASCAT-C PASS REVEALED A BROAD AREA OF GALE-FORCE WINDS IN THE
NORTHERN SEMICIRCLE. A VIGOROUS NORTHEASTERLY COOL SURGE
INTERACTING WITH THE BROAD CIRCULATION OF TROPICAL STORM (TS) 22W
IS MAINTAINING THE ASYMMETRIC WIND FIELD AND ENHANCING THE SURFACE
PRESSURE GRADIENT. THESE OBSERVATIONS SUPPORT HOLDING THE INITIAL
INTENSITY AT 40 KTS WITH HIGH CONFIDENCE, WHICH IS A LITTLE HIGHER
THAN THE SUBJECTIVE DVORAK ESTIMATES. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE MSI.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT
RESULTING FROM A RIDGE OVER NORTHEAST CHINA BUILDING SOUTHEASTWARD
AND A SUBTROPICAL RIDGE (STR) EAST OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 42 KTS AT 040610Z
   CIMSS ADT: 33 KTS AT 040610Z
   CIMSS AIDT: 35 KTS AT 040610Z
   CIMSS D-MINT: 34 KTS AT 040610Z
   CIMSS D-PRINT: 32 KTS AT 040610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR INTRUSION

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 22W HAS SLOWED CONSIDERABLY AND WILL TURN
EQUATORWARD IMMINENTLY AS A RIDGE OVER NORTHEAST CHINA BUILDS
SOUTHEASTWARD. THE SYSTEM WILL CONTINUE SOUTHWARD THROUGH TAU 36 IN
RESPONSE. AT THAT TIME, TS 22W WILL TURN EASTWARD AS IT ENCOUNTERS
THE SOUTHERN PERIPHERY OF A LARGE CYCLONIC CAULDRON OF THE MONSOON
TROUGH SOUTH OF HONSHU. BETWEEN TAU 60 AND TAU 72, A STR EAST OF
HONSHU WILL STEER TS 22W POLEWARD. AFTER TAU 96, AN APPROACHING
TROUGH NEAR HONSHU WILL FLATTEN THE STR, ALLOWING FOR THE
MID-LATITUDE WESTERLIES TO CARRY THE CIRCULATION EASTWARD. FORECAST
CONFIDENCE IS LOW AFTER TAU 72 DUE TO UNCERTAINTY IN THE EVOLUTION
OF TROPICAL DISTURBANCE 97W, ITS POTENTIAL INTERACTION WITH TS 22W
AND THE SURROUNDING STEERING ENVIRONMENT, AND THE EFFECTS OF THE
APPROACHING TROUGH ON THE STR. A WEAKER OR MORE RAPIDLY ERODING STR
COULD RESULT IN AN EARLIER EASTWARD TURN TOWARD THE KANTO PLAIN,
WHILE A STRONGER RIDGE WOULD SUPPORT A MORE POLEWARD TRACK. THE
40-KT FORECAST INTENSITY WILL PERSIST THROUGH TAU 12 DUE TO THE
STRONG PRESSURE GRADIENT BETWEEN TS 22W AND THE NORTHEASTERLY COOL
SURGE. THEREAFTER, THE SYSTEM WILL WEAKEN AS THE SURGE EASES AND
THE PRESSURE GRADIENT RELAXES. AS TS 22W WEAKENS TO 30 KTS, IT WILL
MOVE INTO A MORE FAVORABLE ENVIRONMENT OF LOWER SHEAR AND HIGHER
MOISTURE CONTENT. HOWEVER, THE INTENSITY WILL REMAIN AT 30 KTS FOR
A TIME AS IT MIXES OUT THE ENTRENCHED DRY AIR AND REORGANIZES ITS
INNER-CORE STRUCTURE. IF SUFFICIENT ORGANIZATION OCCURS, SLIGHT
REINTENSIFICATION IS POSSIBLE LATE IN THE FORECAST PERIOD AS THE
SYSTEM MAY BENEFIT FROM ENHANCED OUTFLOW ASSOCIATED WITH AN
UPPER-LEVEL JET STREAK AHEAD OF A PASSING TROUGH TO THE NORTH.

MODEL DISCUSSION: MODEL AGREEMENT HAS MARGINALLY IMPROVED, WITH
SUBSTANTIAL CROSS-TRACK SPREAD PERSISTING IN THE LONG RANGE. GFS,
HAFS-A, AND AI-GFS REPRESENT THE FASTEST AND MOST EQUATORWARD
SOLUTIONS, BRINGING TS 22W NEAR THE KANTO PLAIN. A SECOND CLUSTER,
INCLUDING AIFS, THE AI-GEFS ENSEMBLE MEAN, AND THE EXPERIMENTAL
GOOGLE DEEPMIND MODEL, TRACKS THE SYSTEM INTO WAKAYAMA PREFECTURE.
A THIRD GROUP, CONSISTING OF ECMWF, THE ECENS ENSEMBLE MEAN, THE
UK-MET ENSEMBLE MEAN, AND NAVGEM, FAVORS MOVEMENT TOWARD WESTERN
HONSHU. THE JTWC FORECAST TRACK HAS CHANGED LITTLE FROM THE
PREVIOUS FORECAST THROUGH TAU 72. AFTER TAU 72, THE FORECAST HAS
BEEN SLIGHTLY SHIFTED TOWARD THE CENTRAL GUIDANCE CLUSTER AS THE
GUIDANCE ENVELOPE HAS MODESTLY TIGHTENED AROUND THAT SCENARIO. THE
JTWC INTENSITY FORECAST IS LARGELY UNCHANGED AND LIES NEAR THE
CONSENSUS. IT FOLLOWS THE GENERAL WEAKENING TREND FROM TAU 12 TO
TAU 36 DEPICTED BY HAFS-A, GFS, COAMPS-TC, AND DEEPMIND. GUIDANCE
INDICATES A SLIGHT INTENSITY INCREASE AS TS 22W APPROACHES HONSHU,
WHICH IS REFLECTED IN THE FORECAST.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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