Advisories

WDPN33 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 35.4N 153.7E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 663 NM EAST-SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 22 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 
(TY) 27W UNDERGOING RAPID DYNAMICAL SHEARING UNDER THE INFLUENCE 
OF VERY HIGH SOUTHWESTERLY VERTICAL WIND SHEAR (VWS). THE VORTEX 
HAS UNDERGONE RAPID DECOUPLING, WITH THE LOW-LEVEL CIRCULATION 
CENTER (LLCC) NOW FULLY EXPOSED ON THE SOUTHWESTERN (UPSHEAR) 
FLANK, WHILE THE MID-TO-UPPER-LEVEL ROTATION AND ASSOCIATED DEEP 
CONVECTION ARE DISPLACED NORTHEASTWARD. A 130544Z SSMIS 91GHZ 
MICROWAVE PASS RESOLVES THE SHALLOW LOW-LEVEL DECOUPLED VORTEX TO 
GOOD EFFECT, EXHIBITING SHALLOW BANDING FEATURES ARRAYED ACROSS 
THE SOUTHWESTERN SEMICIRCLE OF THE CIRCULATION, OVERLAID BY AN 
INTRUSION OF DRY MID-LEVEL AIR, WITH STRONG CONVECTION ORGANIZED 
INTO A COMMA-HEAD CONFIGURATION DISPLACED TO THE NORTHEAST. THE 
DEPICTION IN THE MICROWAVE IMAGE STRONGLY SUGGESTS THE SYSTEM IS 
IN THE INITIAL STAGES OF EXTRATROPICAL TRANSITION (ETT). THE INITIAL 
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED 
LLCC RESOLVED IN THE MSI. THE INITIAL INTENSITY IS ASSESSED WITH 
LOW CONFIDENCE. ANALYSIS OF RECENT ASCAT ULTRA-HIGH RESOLUTION (UHR) 
AND SYNTHETIC APERTURE RADAR (SAR) DATA SUPPORTED A RE-ANALYSIS OF 
INTENSITY AT 121800Z AND 130000Z TO 85 KTS AND 80 KTS, RESPECTIVELY. 
THE INITIAL INTENSITY IS ESTIMATED AT 70 KNOTS, BASED ON A BLEND OF 
THE CIMSS SATCON AND AN EXTRAPOLATION OF THE RECENT REMOTELY SENSED 
DATA. ENVIRONMENTAL CONDITIONS ARE HIGHLY UNFAVORABLE, CHARACTERIZED 
BY EXTREMELY HIGH VWS (30-40 KTS), COOL SEA SURFACE TEMPERATURES (24-
25C), MID-LEVEL DRY AIR ENTRAINMENT, AND VERTICAL VORTEX DECOUPLING.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SAR AND ASCAT
DATA. 

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 80 KTS AT 130510Z
   CIMSS ADT: 41 KTS AT 130540Z
   CIMSS AIDT: 56 KTS AT 130540Z
   CIMSS D-MINT: 56 KTS AT 130544Z
   CIMSS D-PRINT: 54 KTS AT 130540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: RAPID VORTEX DECOUPLING. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 27W IS TRACKING NORTHEASTWARD AT ABOUT 22
KNOTS ALONG THE NORTHWESTERN FLANK OF THE STR TO THE SOUTHEAST. 
NO SIGNIFICANT CHANGE IN TRANSLATION SPEED IS EXPECTED THROUGH 
THE FORECAST PERIOD. AS THE SYSTEM CONTINUES TO SHALLOW OUT, IT 
WILL BECOME STEERED BY LOWER-TROPOSPHERIC FLOW ALONG A WEAK RIDGING 
BRANCH EXTENDING NORTHWARD, WHICH GRADUALLY RETREATS EASTWARD. 
THIS ORIENTATION WILL LIMIT FURTHER ACCELERATION DURING ETT, 
ENFORCING A STEADY 20-KNOT TRANSLATION SPEED. ETT WILL PROGRESS 
SLOWLY AS THE CYCLONE TRANSLATES BENEATH A 200MB RIDGE AXIS THAT 
DISPLACES THE POLAR JET STREAM NORTHWARD OVER THE ALEUTIANS. TY 
27W IS NOT PROJECTED TO INTERSECT THE DIVERGENT SECTOR OF THE JET 
MAX UNTIL TAU 48, COINCIDENT WITH THE PROJECTED COMPLETION OF ETT. 
REGARDING INTENSITY, 27W IS FORECAST TO STEADILY WEAKEN AS THE 
REMNANT VORTEX SPINS DOWN. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
STRONG AGREEMENT, EXHIBITING MINIMAL ALONG-TRACK SPEED BIAS AND A 
GRADUAL INCREASE IN CROSS-TRACK SPREAD TO 150 NM BY TAU 48. THE JTWC 
FORECAST TRACK IS COINCIDENT WITH THE MULTI-MODEL CONSENSUS (CONW) 
MEAN WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN SOLID 
CONSENSUS, WITH ALL MEMBERS DEPICTING A PROGRESSIVE DECAY SHAPE. 
CTCX AND DECAY-SHIPS (GFS-BASED) REPRESENT OUTLIERS IN DEPICTING 
UNREALISTIC SYSTEM DISSIPATION WITHIN THE NEXT 36 HOURS, DISCOUNTED 
IN DEFERENCE TO THE REMAINING GUIDANCE SUITE, WHICH IS CONSISTENT 
WITH THE JTWC FORECAST. 

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