Advisories

WDPN33 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 27W (KOGUMA) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 155.5E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 608 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 
27W (KOGUMA) WITH A HIGHLY COMPACT CORE OF DEEP CONVECTION AND A 
DIMPLE EYE SLIGHTLY OFFSET TO THE NORTH OF THE CONVECTIVE MASS. 
CLOUD TOPS ARE VERY COLD WITH TEMPERATURES MEASURING COLDER THAN 
-70 C ENTIRELY SURROUNDING THE SMALL EYE. THE SYSTEM IS ANALYZED 
TO HAVE RAPIDLY INTENSIFIED FROM 60 KTS TO 95 KTS OVER THE PAST 
24 HOURS. A LACK OF RECENT HIGH-RESOLUTION MICROWAVE IMAGERY 
PRECLUDES INSIGHT INTO THE OVERALL STRUCTURE OF THE CORE. THE 
LAST USEFUL MICROWAVE IMAGE WAS A 090228Z AMSR3 89 GHZ IMAGE, 
WHICH SHOWED AN EXTREMELY COMPACT INNER-CORE WITH THE COLD 
BRIGHTNESS TEMPERATURES MEASURING JUST 30 NM IN DIAMETER. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE 
IN ANIMATED MSI. THE INITIAL INTENSITY OF 95 KTS IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS 
INTENSITY ESTIMATES LISTED BELOW. THEINITIAL INTENSITY IS SET ON 
THE HIGH-END OF DVORAK-BASED ESTIMATES DUE TO THE KNOWN LOW BIAS 
FOR EXTREMELY COMPACT SYSTEMS. ENVIRONMENTAL ANALYSIS INDICATES 
THAT 27W REMAINS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED 
BY STRONG OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND 
WARM (29-30 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T5.0 - 90 KTS
   CIMSS SATCON: 85 KTS AT 090510Z
   CIMSS ADT: 79 KTS AT 090610Z
   CIMSS AIDT: 79 KTS AT 090610Z
   CIMSS D-MINT: 85 KTS AT 090255Z
   CIMSS D-PRINT: 103 KTS AT 090610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND 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 AND BEGIN 
A NORTHWARD TRACK THROUGH TAU 72. FOLLOWING TAU 72, TRACK SPEEDS 
WILL START TO INCREASE AS THE SYSTEM TRAVERSES THE NORTHWESTERN 
EXTENT OF THE STR AND TRACKS NORTHEASTWARD THROUGH TAU 120. IN 
TERMS OF INTENSITY, 27W IS FORECAST TO CONTINUE RAPIDLY 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. AROUND TAU 48, SOUTHWESTERLY SHEAR WILL 
INCREASE, INITIATING A 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 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 120 DESPITE THE OTHERWISE HIGHLY UNFAVORABLE ENVIRONMENT. 
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 120 WITH 
COMPLETION OCCURRING JUST OUTSIDE OF THE 5-DAY FORECAST PERIOD.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT 
THROUGH TAU 72 WITH THE NOTABLE EXCEPTION OF JGSM, WHICH IS MUCH 
SLOWER AND WEST OF THE REMAINDER OF GUIDANCE. DISCOUNTING THE 
OUTLIER, CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO BE ABOUT 90 
NM, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST THROUGH THAT 
TIMEFRAME. AFTER TAU 72, MODELS FAN OUT, BUT GENERALLY AGREE ON THE 
OVERALL TRACK PHILOSOPHY. CROSS-TRACK SPREAD AT TAU 120 IS ABOUT 370 
NM WITH THE EC-AIFS BEING THE WESTERNMOST TRACKER WHILE GALWEM AND
UKMET MAKE UP THE EASTERNMOST. THE JTWC TRACK FORECAST IS PLACED
NEAR THE MODIFIED CONSENSUS (WITHOUT JGSM) THROUGH TAU 72, AND THEN
CLOSER TO THE ECMWF AND GOOGLE DEEPMIND ENSEMBLE MEANS THROUGH TAU
120. INTENSITY GUIDANCE IS SLIGHTLY SPLIT WITH MULTIPLE RAPID
INTENSIFICATION (RI) AIDS CONTINUING TO TRIGGER, SUGGESTING A PEAK
INTENSITY OF 120-140 KTS. ON THE OTHER HAND, HAFS-A HAS BECOME ONE
OF THE LEAST AGGRESSIVE MODELS, SHOWING A PEAK OF ONLY 105 KTS.
MODELS THEN AGREE ON WEAKENING AFTER TAU 36. THE JTWC INTENSITY
FORECAST IS SET CLOSER TO THE RI AIDS THROUGH TAU 36, AND THEN
FOLLOWS THE CONSENSUS THROUGH TAU 120 WITH MEDIUM CONFIDENCE.

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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