WDPN31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.7N 143.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1074 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION (TD) 12W IS STRUGGLING UNDER HIGH (30-35 KNOTS)
NORTHERLY VERTICAL WIND SHEAR (VWS) AS EVIDENCED IN ANIMATED WATER
VAPOR IMAGERY, WHICH SHOWS A SHARP UPPER-LEVEL TROUGH DIGGING SOUTHWARD 
TOWARD THE NORTHERN PERIPHERY OF THE SYSTEM. ANIMATED ENHANCED INFRARED 
(EIR) SATELLITE IMAGERY INDICATES THAT THE LOW-LEVEL CIRCULATION CENTER 
(LLCC) HAS DECOUPLED, WITH DEEP CONVECTION CONFINED TO THE EASTERN 
SEMICIRCLE.  THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED 
ON THE EXPOSED CENTER IN EIR IMAGERY. HOWEVER, IT SHOULD BE NOTED THAT 
THE TRACK MOTION IS NOW QUASI-STATIONARY, WITH LITTLE MOVEMENT OVER THE 
PAST FEW HOURS. A 251554Z AMSR2 89GHZ COLOR COMPOSITE MICROWAVE IMAGE
CONTINUES TO REVEAL TIGHTLY WRAPPED SHALLOW BANDING AND A WELL-
ORGANIZED LOW-LEVEL CIRCULATION. HOWEVER, EXTENSIVE DEEP CONVECTIVE 
BANDING IS DISPLACED OVER THE EASTERN AND SOUTHERN SEMICIRCLES. THE 
INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON 
RECENT ASCAT DATA AND THE PGTW, RCTP, KNES DVORAK ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 39 KTS AT 251538Z
   CIMSS ADT: 35 KTS AT 251730Z
   CIMSS AIDT: 35 KTS AT 251730Z
   CIMSS D-MINT: 34 KTS AT 251556Z
   CIMSS D-PRINT: 32 KTS AT 251900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W IS FORECAST TO TRACK
NORTHWARD THROUGH TAU 72 ALONG THE WESTERN PERIPHERY OF THE STR.
AFTER TAU 72, THE SYSTEM WILL TURN NORTHEASTWARD AS THE STR
REORIENTS. THIS IS NOT A RECURVATURE SCENARIO WITH EXTRA-TROPICAL
TRANSITION. THE SYSTEM IS NOT EXPECTED TO ACCELERATE AND WILL NOT
ENCOUNTER THE MIDLATITUDE WESTERLIES UNTIL AFTER THE FORECAST
PERIOD. INSTEAD, THE SYSTEM WILL TRACK ALONG THE NORTHWESTERN
PERIPHERY OF THE STR WITHIN A REVERSE TROUGH FORMATION, WITH THE
SURFACE TROUGH EXTENDING FROM TAIWAIN NORTHEASTWARD TO THE SYSTEM.
ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE, WITH THE HIGH
VWS OFFSET BY VIGOROUS EQUATORWARD OUTFLOW, WHICH IS FUELING THE
RAPIDLY CYCLING DEEP CONVECTIVE BURSTS. THEREFORE, THE INTENSITY IS
EXPECTED TO REMAIN RELATIVELY FLAT THROUGH TAU 72. AFTER TAU 48,
THE VWS SHOULD RELAX, WITH IMPROVED EASTWARD OUTFLOW. HOWEVER, THE
SYSTEM IS EXPECTED TO ENTRAIN DRY AIR ASSOCIATED WITH THE DEEP
MIDLATITUDE TROUGH. AFTER TAU 72, ENVIRONMENTAL CONDITIONS WILL
IMPROVE, WITH A RE-MOISTENING PHASE, ENHANCED POLEWARD OUTFLOW AND
INTENSIFICATION TO TYPHOON STRENGTH BY TAU 120.       

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN GOOD
AGREEMENT THROUGH TAU 72, WITH A 100NM CROSS-TRACK SPREAD AT TAU
72. AFTER TAU 72, GUIDANCE DIVERGES, WITH SIGNIFICANT DIFFERENCES
IN TRACK SPEEDS AND THE EXACT RECURVE POINT. RELIABLE INTENSITY
GUIDANCE SUGGESTS INTENSIFICATION THROUGH TAU 36, WHICH DOESN'T
MAKE SENSE CONSIDERING THE CLEARLY EVIDENT HIGH VWS IMPACTING THE
SYSTEM. AFTER TAU 36, THE INTENSITY GUIDANCE SHOWS A WEAKENING
TREND THEN FLAT TREND THROUGH TAU 84. AFTER TAU 84, THE INTENSITY
GUIDANCE REVEALS A SHARP INTENSIFICATION TREND. THE 251200Z
COAMPS-TC ENSEMBLE ALSO SHOWS POTENTIAL FOR MODERATE
INTENSIFICATION AFTER TAU 72, WITH 40-60 PERCENT PROBABILITIES.   

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