Advisories

WDPN33 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 160.1E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 835 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 27W (KOGUMA) WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) THAT IS STEADILY BECOMING FURTHER EMBEDDED UNDERNEATH
THE CENTRAL DENSE OVERCAST (CDO). THE NORTHEASTERLY SHEAR APPEARS
TO BE BACKING OFF, INDICATED BY THE CDO EXPANDING TO THE NORTH. 
THE CONVECTIVE BURSTS HAVE ALSO BECOME MORE VIGOROUS OVER THE PAST 
6 HOURS WITH OVERSHOOTING TOPS NOW MEASURING COLDER THAN -90 C IN
SOME AREAS. A 080510Z SSMIS 91 GHZ MICROWAVE IMAGE REVEALED A
DEFINED CURVED BAND OF CONVECTION WRAPPING INTO THE CENTER ALONG
THE SOUTHERN SEMICIRCLE OF 27W. THE SAME IMAGE ALSO SHOWED TIGHTLY
CURVED LOW-LEVEL CLOUD LINES OUTLINING THE LLCC WITHIN THE NORTHERN
SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE ANIMATED MSI AND SSMIS MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.5 - 55 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS SATCON: 50 KTS AT 080216Z
   CIMSS ADT: 51 KTS AT 080550Z
   CIMSS AIDT: 45 KTS AT 080550Z
   CIMSS D-MINT: 47 KTS AT 080510Z
   CIMSS D-PRINT: 52 KTS AT 080550Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 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: TS 27W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR
THROUGH TAU 72. THE SYSTEM WILL THEN TURN NORTHWARD AS IT TRAVERSES
THE WESTERN EXTENT OF THE STR THROUGH TAU 120. REGARDING INTENSITY,
27W IS FORECAST TO RAPIDLY INTENSIFY THROUGH TAU 48 TO A PEAK OF
AROUND 120 KTS AS THE ENVIRONMENT REMAINS HIGHLY FAVORABLE AND THE
CIRCULATION RETAINS ITS COMPACT SIZE. AFTER TAU 48, OCEAN HEAT
CONTENT WILL LOWER AND VERTICAL WIND SHEAR WILL BEGIN TO INCREASE.
BY TAU 96, 27W WILL APPROACH THE 26 C SST ISOTHERM AND SOUTHWESTERLY
SHEAR IS EXPECTED TO INCREASE TO OVER 20 KTS, FURTHER SUPPORTING
THE WEAKENING TREND. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT 
THROUGH TAU 72 WITH NO NOTABLE OUTLIERS PRESENT. THE CROSS-TRACK 
SPREAD AT TAU 72 IS MEASURED TO BE ABOUT 180 NM, LENDING HIGH 
CONFIDENCE TO THE JTWC TRACK FORECAST THROUGH THAT TIMEFRAME. AFTER 
TAU 72, THE GUIDANCE DIVERGES SIGNIFICANTLY. THE SPEED OF ADVANCE 
AROUND THE RIDGE VARIES QUITE A BIT BETWEEN MODELS, CAUSING THE 
CROSS-TRACK SPREAD TO INCREASE TO OVER 500 NM AT TAU 120. SOME 
MODELS, SUCH AS THE UKMET AND THE GFS ENSEMBLE MEAN ARE VERY FAST 
AROUND THE RIDGE WHILE THE GOOGLE DEEPMIND AND EC-AIFS ARE MUCH 
SLOWER. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL 
CONSENSUS THROUGH TAU 72 AND THEN CLOSER TO THE ECMWF DETERMINISTIC 
AND GOOGLE DEEPMIND ENSEMBLE MEAN TRACKERS THROUGH TAU 120. INTENSITY 
GUIDANCE NEARLY UNANIMOUSLY AGREES ON RAPID INTENSIFICATION THROUGH 
TAU 48. PEAK INTENSITIES RANGE FROM 110-130 KTS WITH COAMPS-TC BEING 
THE MOST AGGRESSIVE MODEL. GUIDANCE THEN ALSO AGREES ON WEAKENING 
FOLLOWING TAU 60. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO 
THE RI CONSENSUS (RICN) THROUGH TAU 48, AND THEN SLIGHTLY HIGHER 
THAN THE CONSENSUS THROUGH TAU 120 WITH OVERALL 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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