WDPN31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA)        
WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2N 145.1E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 950 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAPIDLY 
CYCLING, INTENSE CONVECTION ASSOCIATED WITH THE CENTRAL DENSE OVERCAST 
(CDO) FEATURE. EIR IMAGERY SHOWS VORTICAL HOT TOWERS FLARING WITHIN 
THE CDO, WITH CLOUD TOP TEMPERATURES NEAR -88C. A 262102Z WSFM 37GHZ 
COLOR COMPOSITE MICROWAVE IMAGE REVEALS CONVECTIVE BANDING WRAPPING 
INTO A BROAD, DEFINED LOW-LEVEL CIRCULATION CENTER POSITIONED ON THE 
SOUTHWEST EDGE OF THE SYMMETRIC CORE CONVECTION. THE INITIAL POSITION 
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE WSFM IMAGE. ANIMATED 
WATER VAPOR RGB IMAGERY INDICATES ROBUST POLEWARD AND EQUATORWARD 
OUTFLOW, WITH SOME PRESSURE OVER THE NORTHWESTERN PERIPHERY OF THE 
SYSTEM. DESPITE PERSISTENT HIGH (30 KNOTS) VERTICAL WIND SHEAR, TS 12W 
IS OVERCOMING THIS PRESSURE, WITH EXPANDING WESTWARD AND NORTHWESTWARD 
OUTFLOW. EXTENSIVE DRY AIR IS PRESENT OVER THE WESTERN PERIPHERY BUT 
IS NO LONGER HAVING A SIGNIFICANT IMPACT ON THE SYSTEM. THE INITIAL 
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE HEDGED BELOW 
THE AGENCY DVORAK ESTIMATES BASED ON THE CONVECTIVE STRUCTURE EVIDENT 
IN MICROWAVE IMAGERY. CIMSS OBJECTIVE ESTIMATES RANGE FROM 47 TO 64 
KNOTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 61 KTS AT 270000Z
   CIMSS ADT: 53 KTS AT 270000Z
   CIMSS AIDT: 47 KTS AT 270000Z
   CIMSS D-PRINT: 64 KTS AT 262300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR OVER THE WESTERN PERIPHERY

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

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
POLEWARD THROUGH TAU 72 ALONG THE WESTERN PERIPHERY OF THE DEEP-
LAYERED STR TOWARD A BREAK IN THE STR MAINTAINED BY A SERIES OF 
MIDLATITUDE SHORTWAVE TROUGHS. TS 12W WILL INTENSIFY OVER THE NEXT
24 HOURS TO A PEAK OF 75 KNOTS AS THE SYSTEM CONTINUES TO REMOISTEN 
AND CONSOLIDATE WITH PERSISTENT CORE CONVECTION. HOWEVER, HIGH 
NORTHERLY VERTICAL WIND SHEAR COULD CONTINUE TO HINDER MORE 
SIGNIFICANT DEVELOPMENT. AFTER TAU 36, DRY AIR ENTRAINMENT IS 
ANTICIPATED, WHICH WILL LIKELY LEAD TO A BRIEF PERIOD OF SLIGHT 
WEAKENING. AFTER TAU 72, A STR WILL BUILD TO THE NORTH EFFECTIVELY 
SLOWING THE POLEWARD PROGRESSION. CURRENTLY, THE SYSTEM IS EXPECTED TO 
TURN NORTHEASTWARD. HOWEVER, THE EXACT TRACK MOTION IS UNCERTAIN DUE 
TO COMPETING STEERING INFLUENCES THAT DEVELOP IN THE LATER FORECAST 
PERIOD. THE SYSTEM IS FORECAST TO REACH ITS PEAK INTENSITY DURING THIS 
EXTENDED PERIOD AS THE CORE REMOISTENS, VERTICAL WIND SHEAR DECREASES, 
AND POLEWARD OUTFLOW IMPROVES INTO A DEEP MIDLATITUDE MAJOR SHORTWAVE 
TROUGH TO THE NORTHEAST.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT AGREEMENT 
THROUGH TAU 48. HOWEVER, GUIDANCE DIVERGES QUICKLY BY TAU 72. THE 
CROSS-TRACK SPREAD AT TAU 72 IS ABOUT 135NM, WHICH INDICATES THE 
INCREASING UNCERTAINTY IN THE JTWC TRACK FORECAST. AFTER TAU 72, 
GUIDANCE DIVERGES FURTHER WITH LOW CONFIDENCE IN THE JTWC TRACK 
FORECAST. THE 261200Z ECENS ENSEMBLE AND 261800Z GEFS ENSEMBLE ALSO 
INDICATE LARGE SPREAD IN THE PROBABILISTIC GUIDANCE AFTER TAU 48, WITH 
ABOUT 30 PERCENT OF THE SOLUTIONS TRACKING THE SYSTEM WESTWARD TO 
NORTHWESTWARD. HOWEVER, THE LARGE MAJORITY OF SOLUTIONS INDICATE A 
NORTHWARD TO NORTHEASTWARD TRACK, WHICH SUPPORTS THE JTWC EXTENDED 
PERIOD FORECAST WITH LOW CONFIDENCE. RELIABLE INTENSITY GUIDANCE 
INDICATES A SHORT-TERM PEAK INTENSITY OF 62 TO 73 KNOTS WHILE THE 
MAJORITY OF THE GUIDANCE SHOWS A PERIOD OF WEAKENING FROM TAU 24 TO 
TAU 84. AFTER TAU 84, THE INTENSITY GUIDANCE INDICATES 
REINTENSIFICATION TO A SECONDARY PEAK OF 80 TO 95 KNOTS.   

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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