Advisories

WDPN33 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.9N 151.7E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 598 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
27W (KOGUMA) ACCELERATING NORTHEASTWARD WITH A PARTIALLY EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) AND FLARING PUFFS OF CENTRAL 
CONVECTION THAT ARE QUICKLY SHEARED AWAY. A 122007Z RCM-3 SAR PASS
REVEALS A SLIGHTLY ASYMMETRICAL WIND FIELD ERODED ON THE NORTHERN
QUADRANT, SUPPORTED BY A LATER 122334Z METOP-B ASCAT PASS THAT
REFLECTS THE SAME WEAKNESS. ENVIRONMENTAL CONDITIONS ARE ASSESSED
AS HIGHLY UNFAVORABLE AS 27W IS WITHIN COOL (25-26 C) SEA SURFACE
TEMPERATURES AND EXPERIENCES HIGH (OVER 30 KTS) VERTICAL WIND SHEAR
AS IT NEARS THE UPPER LEVEL WESTERLIES, CAUSING DRY AIR ENTRAINMENT, 
VISIBLE ON THE EASTERN FLANK OF THE SYSTEM IN MSI. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE TIMELY
ASCAT DATA. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE
BASED ON THE WIDENING SPREAD OF INTENSITY GUIDANCE, BUT HEDGED
CLOSER TO THE AFOREMENTIONED WIND SPEED DATA WHICH SUGGEST 65-85
KTS, WHILE THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE ESTIMATES
LISTED BELOW ARE LOWER AS 27W APPROACHES EXTRATROPICAL
TRANSITION (ETT), WHICH THE DVORAK METHOD IS KNOWN TO STRUGGLE
WITH.

INITIAL WIND RADII BASIS: 122007Z RCM-3 SAR DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE
SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 58 KTS AT 122115Z
   CIMSS ADT: 45 KTS AT 122330Z
   CIMSS AIDT: 46 KTS AT 122330Z
   CIMSS D-MINT: 52 KTS AT 122316Z
   CIMSS D-PRINT: 50 KTS AT 130010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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 FORECAST TO CONTINUE ACCELERATING
NORTHEASTWARD UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE
(STR) CENTERED TO THE SOUTHEAST. KOGUMA IS RAPIDLY APPROACHING THE
BAROCLINIC ZONE AND UPPER-LEVEL WESTERLIES, AND EXTRATROPICAL
TRANSITION (ETT) IS FORECAST TO BEGIN NO LATER THAN TAU 24 AND
COMPLETE NO LATER THAN TAU 48, ALTHOUGH THERE IS A POSSIBILITY FOR
ONSET TO BEGIN SOONER AS THE SYSTEM ACCELERATES TOWARDS THE
UPPER-LEVEL JET. REGARDING INTENSITY, TY 27W IS EXPECTED TO
CONTINUE TO STEADILY WEAKEN AS VWS CONTINUES TO INCREASE, CAUSING
FURTHER DRY AIR ENTRAINMENT. KOGUMA IS EXPECTED TO REMAIN ABOVE
TROPICAL STORM INTENSITY AT THE TIME IT COMPLETES ETT.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE
REMAINDER OF THE FORECAST PERIOD, WITH A CROSS-TRACK SPREAD OF 100
NM AND AN ALONG-TRACK SPREAD OF 65 NM AT TAU 48. THE OFFICIAL JTWC
FORECAST IS ASSESSED WITH HIGH CONFIDENCE, CLOSELY IN LINE WITH THE
MULTI-MODEL CONSENSUS. MODEL INTENSITY GUIDANCE IS ALSO IN GOOD
AGREEMENT ON A STEADY WEAKENING PHASE FOR THE REMAINDER OF THE
FORECAST PERIOD, WITH THE ONLY OUTLIERS BEING THE NAVGEM BASED
COAMPS-TC WHICH DEPICTS A SHARPER WEAKENING TREND. THE OFFICIAL
JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE FOR THE
REMAINDER OF THE FORECAST PERIOD, CLOSELY IN LINE WITH THE
MULTI-MODEL CONSENSUS AND GOOGLE DEEPMIND.

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