WDPN31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA)        
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 144.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 996 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CENTRAL 
DENSE OVERCAST FEATURE OBSCURING THE LOW-LEVEL CIRCULATION. HOWEVER, A 
261844Z SSMIS 37GHZ MICROWAVE IMAGE REVEALS A WELL-DEFINED MICROWAVE 
EYE FEATURE, WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. 
ANIMATED WATER VAPOR RGB IMAGERY INDICATES IMPROVING POLEWARD OUTFLOW 
AND ROBUST EQUATORWARD OUTFLOW. ADDITIONALLY, THE SYSTEM IS OVERCOMING 
THE STRONG NORTHERLY FLOW ASSOCIATED WITH A SHARP UPPER-LEVEL TROUGH, 
WITH EXPANDING 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 55 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE HEDGED BELOW THE AGENCY DVORAK ESTIMATES BASED ON
THE MICROWAVE EYE FEATURE AND OVERALL CONVECTIVE STRUCTURE.

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: T4.5 - 77 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 45 KTS AT 261800Z
   CIMSS AIDT: 40 KTS AT 261800Z
   CIMSS D-MINT: 49 KTS AT 261843Z
   CIMSS D-PRINT: 50 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 25-30 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: SYSTEM IS MOISTENING FASTER THAN
EXPECTED; THEREFORE, THE JTWC INTENSITY FORECAST IS ADJUSTED HIGHER
IN THE EARLY FORECAST PERIOD.

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 
TO 36 HOURS 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 216NM, WHICH INDICATES THE 
INCREASING UNCERTAINTY IN THE JTWC TRACK FORECAST. AFTER TAU 72, 
GUIDANCE DIVERGES WITH LOW CONFIDENCE IN THE JTWC TRACK FORECAST. THE 
261200Z ECENS AND GEFS ENSEMBLES 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 57 TO 67 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 75 TO 85 
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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