Advisories

WDPN33 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 154.1E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 558 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
27W (KOGUMA), SURPRISINGLY, UNDERGOING AN EYEWALL REPLACEMENT CYCLE
(ERC) WITH AN EXPANDING CENTRAL DENSE OVERCAST (CDO) AND A
GENERALLY BROADENING APPEARANCE. THE ERC WAS CAPTURED BY 090731Z
WSFM 89 GHZ AND 090759Z GMI 89 GHZ MICROWAVE IMAGES. THE IMAGES
SHOW THE DEGRADING EXTREMELY COMPACT INNER-CORE SURROUNDED BY A
STRONGER, OUTER EYEWALL. ADDITIONALLY, A 090752Z RCM-3 SAR PASS
REVEALED DUAL WIND MAXIMUMS, FURTHER SUPPORTING THE ASSESSMENT OF
AN ONGOING ERC. THE SAR MEASURED A VMAX OF 104 KTS WITHIN THE
NORTHEASTERN QUADRANT OF THE INNER EYEWALL. CLOUD TOPS ALSO STARTED
WARMING AT 091000Z, THOUGH THE SYSTEM APPEARS TO BE REORGANIZING
RIGHT AROUND 091200Z WITH A WARMING EYE AND IMPROVING SYMMETRY. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN
ANIMATED EIR. THE INITIAL INTENSITY OF 100 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED SAR PASS ALONG WITH
THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED BELOW. IT IS
WORTH NOTING THAT ADT HAS BEEN CONSISTENTLY UNDERESTIMATING THE
INTENSITY FOR 27W.

INITIAL WIND RADII BASIS: 090752Z RCM-3 SAR DATA 

CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS ADT: 61 KTS AT 091200Z
   CIMSS AIDT: 85 KTS AT 091200Z
   CIMSS D-MINT: 103 KTS AT 090959Z
   CIMSS D-PRINT: 93 KTS AT 091200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

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 TRACKING
NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH
TAU 48. 27W WILL THEN APPROACH THE RIDGE AXIS, CAUSING THE
TRAJECTORY TO BECOME GENERALLY NORTHWARD THROUGH TAU 72. FOLLOWING
TAU 72, TRACK SPEEDS WILL START TO INCREASE AS THE SYSTEM TRAVERSES 
THE NORTHWESTERN EXTENT OF THE STR AND ACCELERATES NORTHEASTWARD 
THROUGH TAU 120. EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 
120 WITH COMPLETION OCCURRING JUST OUTSIDE OF THE 5-DAY FORECAST 
PERIOD. IN TERMS OF INTENSITY, 27W IS FORECAST TO RECOVER FROM THE 
ERC 
AND CONTINUE INTENSIFYING THROUGH TAU 24 TO A PEAK OF AROUND 120 KTS.
AFTER TAU 24, 27W IS EXPECTED TO LOSE THE ROBUST EQUATORWARD
OUTFLOW CHANNEL AND SEA SURFACE TEMPERATURES WILL START TO DROP,
CAUSING THE INTENSIFICATION TREND TO COME TO A HALT. AS A RESULT,
27W IS FORECAST TO MAINTAIN OR SLIGHTLY WEAKEN FROM TAU 24 TO TAU
48. AROUND TAU 60, SOUTHWESTERLY SHEAR WILL START TO INCREASE,
INITIATING A STEADY WEAKENING TREND THAT WILL PERSIST THROUGH THE
REMAINDER OF THE FORECAST PERIOD. BY TAU 96, SHEAR WILL INCREASE TO
OVER 50 KTS AND DRY AIR WILL BEGIN GREATLY IMPACTING THE SYSTEM.
HOWEVER, 27W WILL TAP INTO AN EXTREME POLEWARD OUTFLOW CHANNEL,
SUPPORTED BY A STRONG JET MAXIMUM TO THE NORTHEAST, WHICH IS
EXPECTED TO ALLOW THE SYSTEM TO MAINTAIN TYPHOON STRENGTH THROUGH
TAU 96 DESPITE THE OTHERWISE HIGHLY UNFAVORABLE ENVIRONMENT.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT THE ENTIRE FORECAST PERIOD WITH THE EXCEPTION OF JGSM
AND NAVGEM. JGSM IS SIGNIFICANTLY SLOWER WHILE NAVGEM IS
SIGNIFICANTLY FASTER. DISCOUNTING THE TWO OUTLIERS, CROSS-TRACK
SPREAD IS MEASURED TO BE JUST 80 NM AT TAU 72 AND 250 NM AT TAU
120. THE JTWC TRACK FORECAST IS PLACED NEAR THE MODIFIED CONSENSUS
(REMOVING THE OUTLIERS) WITH HIGH CONFIDENCE THROUGH TAU 72 AND
MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE REMAINS IN
MODERATE AGREEMENT WITH MULTIPLE RAPID INTENSIFICATION (RI) AIDS
CONTINUING TO TRIGGER, SUGGESTING A PEAK INTENSITY OF 125-140 KTS.
HAFS-A NOW SHOWS A PEAK INTENSITY OF 125 KTS, THOUGH IT
INTERESTINGLY HAS THE PEAK OCCURRING AT TAU 48 RATHER THAN TAU 24.
COAMPS-TC IS MUCH LESS AGGRESSIVE THIS RUN, SHOWING A PEAK OF ONLY
105 KTS. MODELS THEN AGREE ON WEAKENING FROM TAU 48 ONWARD. THE
JTWC INTENSITY FORECAST REMAINS CONSISTENT WITH THE PREVIOUS
FORECAST, SHOWING A PEAK OF 120 KTS AT TAU 24 FOLLOWED BY STEADY
WEAKENING.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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