Advisories

WDPN33 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.5N 167.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 168 NM NORTH OF KWAJALEIN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 27W (KOGUMA) WITH A MOSTLY OBSCURED LOW-LEVEL CIRCULATION
CENTER (LLCC) THAT HAS TUCKED UNDERNEATH BUILDING CONVECTION OVER
THE CENTER. SOUTHERLY VERTICAL WIND SHEAR CONTINUES TO IMPACT THE
SYSTEM, LEAVING THE SOUTHERN PORTION OF THE LLCC SLIGHTLY EXPOSED.
A 051032Z METOP-C ASCAT PASS REVEALED A COMPACT CIRCULATION WITH
GALE-FORCE WINDS LIMITED TO THE NORTHWESTERN QUADRANT. THE INITIAL
POSITION, INTENSITY, AND WIND RADII ARE ALL PLACED WITH HIGH
CONFIDENCE BASED ON THE TIMELY ASCAT DATA. ENVIRONMENTAL ANALYSIS 
INDICATES THAT 27W REMAINS PLACED WITHIN A MARGINALLY FAVORABLE 
ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, 
MODERATE (15-20 KTS) SOUTHERLY SHEAR, AND WARM (29-30 C) SEA 
SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 051032Z METOP-C ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS ADT: 35 KTS AT 051210Z
   CIMSS AIDT: 35 KTS AT 051210Z
   CIMSS D-PRINT: 35 KTS AT 051210Z

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

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

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 12. AROUND TAU 12, 27W WILL BEGIN TO FEEL THE EFFECTS OF THE
SUBTROPICAL RIDGE (STR) TO THE NORTH, WHICH WILL THEN BECOME THE
PRIMARY STEERING MECHANISM. THIS WILL RESULT IN A NORTHWESTWARD
TRAJECTORY THROUGH TAU 96 AS THE SYSTEM TRACKS ALONG THE SOUTHERN
PERIPHERY OF THE STR. 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 70 KTS AS THE
ENVIRONMENT REMAINS MARGINALLY FAVORABLE. THE PRIMARY HINDRANCE IS
EXPECTED TO BE EASTERLY SHEAR, WHICH IS ANTICIPATED TO INCREASE
STARTING AROUND TAU 24. SHEAR IS FORECAST TO DECREASE AFTER TAU 
60, ALLOWING FOR A QUICKER RATE OF INTENSIFICATION. ADDITIONALLY,
POLEWARD OUTFLOW WILL BEGIN TO INCREASE AT TAU 72, FURTHER
SUPPORTING THE INTENSIFICATION TREND. RIGHT AROUND TAU 120,
SOUTHWESTERLY SHEAR WILL BEGIN TO INCREASE, STUNTING FURTHER
INTENSIFICATION. IT IS WORTH NOTING THAT 27W IS EXPECTED TO BE
QUITE COMPACT THROUGHOUT THE FORECAST PERIOD, AND WILL BE HIGHLY
SUSCEPTIBLE TO CHANGES IN THE SURROUNDING ENVIRONMENT. FOR EXAMPLE,
IF SHEAR ENDS UP BEING STRONGER THAN EXPECTED, LESS DEVELOPMENT
COULD OCCUR THAN IS CURRENTLY FORECAST. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT 
THROUGH TAU 72 WITH THE NOTABLE EXCEPTION OF GFS, WHICH IS MUCH 
SLOWER THAN THE REMAINDER OF GUIDANCE. MODEL AGREEMENT AFTER TAU 
72 IS A BIT WORSE THIS MODEL RUN COMPARED TO THE PREVIOUS CYCLE. 
THE CROSS-TRACK SPREAD IS MEASURED TO BE ABOUT 160 NM AT TAU 72, 
BUT THEN FANS OUT TO 320 NM AT TAU 120. NAVGEM IS A SIGNIFICANT
POLEWARD OUTLIER AT TAU 120 AND IS DISREGARDED WHILE THE GOOGLE
DEEPMIND AND EC-AIFS COMPRISES THE SOUTHERNMOST TRACKERS. THE JTWC
TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU
72 AND THEN SLIGHTLY SOUTH OF THE CONSENSUS THROUGH TAU 120, CLOSER
TO THE VARIOUS AI-BASED MODELS. INTENSITY GUIDANCE IS IN MUCH WORSE
AGREEMENT THIS MODEL RUN. COAMPS-TC CONTINUES TO BE SUBSTANTIALLY
MORE AGGRESSIVE IN THE NEAR-TERM THAN THE REMAINDER OF GUIDANCE. IT
DEPICTS AN INTENSITY OF 110 KTS AT TAU 36 WHILE OTHER MODELS RANGE
BETWEEN 40-65 KTS. HWRF HAS ALSO BECOME NOTICEABLY MORE AGGRESSIVE,
SHOWING AN INTENSITY OF 100 KTS AT TAU 60. INTENSITIES AT TAU 120 
RANGE FROM 80 KTS (DECAY SHIPS) TO 140 KTS (COAMPS-TC). THE JTWC 
INTENSITY FORECAST IS PLACED NEAR THE HAFS-A THROUGHOUT THE FORECAST 
PERIOD WITH OVERALL LOW CONFIDENCE. 

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