Advisories

WDPN33 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.0N 168.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 139 NM NORTH OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL 
STORM 27W (KOGUMA) WITH TWO DISTINCT MESOVORTICES REVOLVING AROUND 
A CENTROID WITH DEEP CONVECTION DISPLACED TO THE NORTH. THE DISPLACED 
CONVECTION AND VORTEX TILT IS ATTRIBUTED TO ABOUT 20 KTS OF SOUTHERLY 
SHEAR ACTING ON THE SYSTEM. THE DEFINITION AND SYMMETRY OF THE 
LOW-LEVEL CIRCULATION HAS CLEARLY IMPROVED OVER THE PAST 6 HOURS, 
CORROBORATING THE UPGRADE TO TROPICAL STORM STATUS. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ASSESSED 
CENTER OF THE ROTATING MESOVORTICES IN ANIMATED MSI. THE INITIAL 
INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON HIGH 
END OF THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED 
BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 27W IS IN A MARGINALLY 
FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW 
ALOFT, MODERATE (15-20 KTS) SOUTHERLY VERTICAL WIND SHEAR, AND WARM 
(29-30 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE NORTHWESTERN FLANK OF A NEAR
EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 050540Z
   CIMSS AIDT: 33 KTS AT 050540Z
   CIMSS D-MINT: 35 KTS AT 050228Z
   CIMSS D-PRINT: 25 KTS AT 050540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

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 TRACK GENERALLY NORTHWARD 
UNDER THE INFLUENCE OF THE NER TO THE SOUTHEAST THROUGH TAU 24. AFTER 
TAU 24, THE SUBTROPICAL RIDGE (STR) TO THE NORTH WILL BECOME THE 
PRIMARY STEERING MECHANISM, GUIDING 27W NORTHWESTWARD THROUGH TAU 96. 
NEAR TAU 96, THE SYSTEM WILL APPROACH THE SOUTHWESTERN EXTENT OF THE 
STEERING RIDGE AND BEGIN TO TURN SLIGHTLY MORE POLEWARD THROUGH TAU 
120. REGARDING INTENSITY, 27W IS FORECAST TO GRADUALLY INTENSIFY 
THROUGH TAU 60 TO AROUND 65 KTS AS THE ENVIRONMENT REMAINS MARGINALLY 
FAVORABLE. THE PRIMARY HINDRANCE IS EXPECTED TO BE EASTERLY SHEAR, 
WHICH IS ANTICIPATED TO INCREASE STARTING AT TAU 24. THE SHEAR IS 
FORECAST TO DECREASE AFTER TAU 60, ALLOWING FOR A QUICKER RATE OF 
INTENSIFICATION.  ADDITIONALLY, POLEWARD OUTFLOW WILL BEGIN TO 
INCREASE AT TAU 96, FURTHER SUPPORTING THE INTENSIFICATION TREND. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH NO NOTABLE OUTLIERS PRESENT.
THE CROSS-TRACK SPREAD IS MEASURED TO BE ABOUT 140 NM AT TAU 72 AND
230 NM AT TAU 120. THE GOOGLE DEEPMIND ENSEMBLE MEAN IS SITUATED AS
THE SOUTHERNMOST TRACKER WHILE THE GEFS MEAN IS THE NORTHERNMOST.
THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS
WITH HIGH CONFIDENCE THROUGH TAU 72 AND THEN MEDIUM CONFIDENCE
THROUGH TAU 120. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH
THE NOTABLE EXCEPTION OF COAMPS-TC (GFS-BASED) WHICH SHOWS A MUCH
MORE RAPID RATE OF INTENSIFICATION THROUGH THE FIRST 36 HOURS TO AN
INTENSITY OF 95 KTS. THE REMAINDER OF GUIDANCE GENERALLY AGREES ON
GRADUAL DEVELOPMENT THROUGH TAU 60 FOLLOWED BY QUICKER DEVELOPMENT
THROUGH TAU 120. THE JTWC INTENSITY FORECAST IS PLACED SLIGHTLY
BELOW THE CONSENSUS THROUGH TAU 36 TO OFFSET COAMPS-TC AND THEN
NEAR 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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