WDPN31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA)         
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8N 143.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 121 NM WEST OF ALAMAGAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 24 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 MULTISPECTRAL 
SATELLITE IMAGERY DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION, 
WITH AN OBLONG AREA OF DEEP CONVECTION SHEARED OVER THE SOUTHEAST 
QUADRANT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON 
A 252349Z ASCAT-C BULLS-EYE IMAGE REVEALING A BROAD DEFINED CENTER, 
WITH A BAND OF 40-50 KNOT WINDS OVER THE SOUTHEASTERN AND EASTERN 
QUADRANTS. THE INITIAL INTENSITY OF 50 KNOTS IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE ASCAT-C DATA. THE 34-KNOT AND 50-KNOT WIND 
RADII ARE BASED ON A DETAILED ANALYSIS OF THE ASCAT-C IMAGE.

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: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 39 KTS AT 252148Z
   CIMSS ADT: 35 KTS AT 260000Z
   CIMSS AIDT: 35 KTS AT 260000Z
   CIMSS D-PRINT: 35 KTS AT 260100Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 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 TAIWAN 
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 IS IN OVERALL FAIR 
AGREEMENT THROUGH TAU 72, WITH A 250NM CROSS-TRACK SPREAD AT TAU
72. AFTER TAU 72, GUIDANCE DIVERGES FURTHER, WITH A CLEAR BIFURCATION.
NAVGEM AND AFUM TRACK THE SYSTEM SLOWLY NORTHWESTWARD THEN WESTWARD 
WHILE THE REMAINDER OF THE GUIDANCE RECURVES THE SYSTEM NORTHEASTWARD 
AT VARYING TRACK SPEEDS. RELIABLE INTENSITY GUIDANCE SUGGESTS 
INTENSIFICATION THROUGH TAU 36, WHICH DOESN'T MAKE SENSE CONSIDERING 
THE CLEARLY EVIDENT HIGH VWS IMPACTING THE SYSTEM AND THE PERSISTENT 
HIGH VWS THROUGH AT LEAST TAU 24. AFTER TAU 36, THE INTENSITY GUIDANCE 
SHOWS A WEAKENING TREND THEN FLAT TREND THROUGH TAU 72. AFTER TAU 72, 
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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