WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
040//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 38.3N 145.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 248 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT
TROPICAL STORM (TS) 12W MAINTAINS A SYMMETRICAL AND WELL-ORGANIZED
STRUCTURE, ALTHOUGH THE ASSOCIATED CONVECTION CONTINUES TO WARM AND
WEAKEN. A 021159Z ASCAT-B BULLSEYE PASS REVEALS AN INCREASINGLY
ASYMMETRIC WIND FIELD, BUT A WELL-DEFINED INNER-CORE OF LIGHT WINDS
AND STORM-FORCE WINDS TO THE SOUTH AND SOUTHEAST OF THE TIGHTLY
DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE LLCC DEFINED IN THE
ASCAT DATA NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE HIGHER PGTW DVORAK CURRENT INTENSITY
ESTIMATE (T3.5), THE CIMSS SATCON AND AIDT, SUPPORTED BY THE ASCAT
DATA. ENVIRONMENTAL CONDITIONS ARE RAPIDLY DETERIORATING, WITH
RAPIDLY COOLING SSTS, THOUGH THE MODERATE TO HIGH SOUTHERLY SHEAR
IS OFFSET FOR THE MOMENT BY THE STRONG POLEWARD OUTFLOW, ALLOWING
THE VORTEX TO REMAIN COUPLED.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED EAST OF IWO TO. 

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: 56 KTS AT 021310Z
   CIMSS ADT: 34 KTS AT 021130Z
   CIMSS AIDT: 62 KTS AT 021130Z
   CIMSS D-MINT: 50 KTS AT 020806Z
   CIMSS D-PRINT: 49 KTS AT 021310Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: RAPIDLY DECREASING SSTS.

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
EAST-NORTHEASTWARD THROUGH THE FORECAST PERIOD, ALONG THE NORTHERN
SIDE OF A DEEP STR THAT SHIFTS SOUTHWESTWARD THROUGH TAU 48, THEN
ALONG THE NORTHERN EDGE OF A SEPARATE STR PUSHING WEST OF THE
DATELINE THROUGH TAU 72. TRACK SPEEDS ARE EXPECTED TO INCREASE UP
TO TAU 48, THEN SLOW SLIGHTLY AS THE SYSTEM MOVES THROUGH A
RELATIVELY WEAKER STEERING GRADIENT AS THE PRIMARY STEERING
INFLUENCE SHIFTS FROM THE RIDGE EAST OF JAPAN TO THE RIDGE MOVING
ACROSS THE DATELINE. AS MENTIONED ABOVE, THE SOUTHWESTERLY SHEAR
VECTOR IS CURRENTLY IN PHASE WITH TRACK OF TS 12W, REDUCING THE
RELATIVE SHEAR, AND ALLOWING THE SYSTEM TO MAINTAIN A RELATIVELY
ALIGNED AND COUPLED VORTEX. THIS HAS ALLOWED TS 12W TO MAINTAIN
INTENSITY OVER THE PAST 24 HOURS EVEN IN THE FACE OF OTHERWISE
UNFAVORABLE DEEP-LAYER SHEAR. THE SYSTEM HAS ALSO BEEN MOVING OVER
A TONGUE OF WARM WATERS BUT HAS NOW MOVED AWAY FROM THOSE AND IS
CURRENTLY MOVING ALONG THE GRADIENT BETWEEN THE KUROSHIO CURRENT
AND MUCH COOLER WATERS TO THE NORTH AND EAST. THE SYSTEM IS
FORECAST TO MAINTAIN INTENSITY FOR ANOTHER 12 HOURS, BUT AS IT
CONTINUES TRACKING NORTHEASTWARD, THE SHEAR VECTOR WILL BECOME
INCREASINGLY OUT OF PHASE WITH THE STORM MOTION, WITH THE RESULT OF
RAPIDLY INCREASING DEEP-LAYER SHEAR. THIS WILL USHER IN DRY AIR
INTO THE CORE OF THE SYSTEM AS WELL, LEADING TO STEADY WEAKENING
THROUGH THE REMAINDER OF THE FORECAST. THE SYSTEM WILL BEGIN
EXTRATROPICAL TRANSITION (ETT) BY TAU 48, WITH ETT EXPECTED TO
COMPLETE NO LATER THAN TAU 72, BUT LIKELY AS EARLY AS TAU 60. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT, BOTH IN TERMS OF ALONG- AND CROSS-TRACK SPREAD THROUGH
TAU 48. CROSS-TRACK SPREAD REMAINS GOOD (NEAR 110NM) BY TAU 72, BUT
ALONG-TRACK SPREAD INCREASES SHARPLY AFTER TAU 48, UP TO 350NM
BETWEEN THE SLOW NAVGEM AND FAST GFS. THE JTWC FORECAST IS
POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS MEAN WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS IN OVERALL GOOD AGREEMENT ON THE
OVERALL SCENARIO; HOWEVER THE MAJORITY OF THE GUIDANCE IS TOO FAST
TO WEAKEN THE SYSTEM. THE HAFS-A AND HWRF ARE SLOWER TO WEAKEN THE
SYSTEM AND LIKELY ARE THE MORE ACCURATE DEPICTION OF THE OVERALL
WEAKENING SCENARIO. THUS THE JTWC FORECAST IS PLACED CLOSE TO THE
HAFS-A AND HWRF SOLUTIONS THROUGH THE FORECAST WITH HIGH
CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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