Advisories

WDPN33 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.0N 165.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 321 NM SOUTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SMALL
CENTRAL COLD COVER (CCC) COMPLETELY OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE BURST OF CONVECTION HAS PERSISTED
FOR AT LEAST SIX HOURS, AND CLOUD TOP TEMPERATURES HAVE BEEN AS
COLD AS -92 DEGREES CELSIUS. THE CCC PATTERN IS CONSISTENT WITH
ARRESTED DEVELOPMENT, SUPPORTING THE ASSESSMENT THAT THE INTENSITY
HAS REMAINED NEARLY STEADY WHILE THE PATTERN PERSISTS. A 060649Z
WSF-M MWI PASS INDICATED A VERTICALLY TILTED VORTEX AND A LACK OF A
COHERENT INNER CORE. DESPITE TRAVERSING VERY WARM SEA SURFACE
TEMPERATURES (SST) NEAR 30 DEGREES CELSIUS AND HIGH OCEAN HEAT
CONTENT (OHC), TS 27W CONTINUES TO CONTEND WITH DRY AIR WRAPPING
INTO THE CIRCULATION FROM THE SOUTHWEST AND MODERATE VERTICAL WIND
SHEAR (VWS) OF NEAR 20 KTS. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON A TIGHT CLUSTER OF FIXES FROM PGTW AND
PHFO. THE INITIAL INTENSITY HAS BEEN HELD AT 45 KTS WITH MEDIUM
CONFIDENCE, CONSISTENT WITH THE CCC CLOUD PATTERN AND SUPPORTED BY
THE STEADY SUBJECTIVE AND LOWER-END OBJECTIVE ESTIMATES. THE HIGHER
ADT ESTIMATE IS DISCOUNTED DUE TO THE TILTED VORTEX AND LACK OF A
COHERENT INNER CORE. THE HIGH D-MINT ESTIMATE IS BASED ON A
PARTIAL, LOW-RESOLUTION MICROWAVE IMAGE AND IS ALSO DISCOUNTED.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN EXTENSION OF A MID-LEVEL
SUBTROPICAL RIDGE (STR) BUILDING WESTWARD

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS ADT: 53 KTS AT 061140Z
   CIMSS AIDT: 41 KTS AT 061140Z
   CIMSS D-MINT: 62 KTS AT 061045Z
   CIMSS D-PRINT: 45 KTS AT 061220Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 WILL CONTINUE ON A NORTHWESTWARD
TRAJECTORY THROUGH TAU 12, STEERED BY THE SOUTHERN EXTENSION OF THE
STR. THEREAFTER, THE SYSTEM WILL TURN WEST-NORTHWESTWARD AS THE
MID-LEVEL RIDGE BUILDS WESTWARD. TOWARD THE END OF THE FORECAST
PERIOD, A TROUGH TRAVELING EASTWARD FROM HONSHU WILL INTERACT WITH
TYPHOON (TY) 15E TO CREATE A WEAKNESS IN THE STR, ALLOWING TS 27W
TO TURN NORTHWESTWARD ON A MORE POLEWARD TRACK. THE EVOLUTION OF
THE TROUGH, TY 15E, AND THE STR INTRODUCES SIGNIFICANT UNCERTAINTY
REGARDING THE DEGREE OF THE POLEWARD TURN LATE IN THE FORECAST
PERIOD. THE FORECAST CALLS FOR LIMITED DEVELOPMENT THROUGH TAU 12
DUE TO THE ONGOING CCC PATTERN, VWS, AND DRY AIR ENTRAINMENT.
DESPITE TRAVERSING VERY WARM SST AND HIGH OHC, THE SYSTEM WILL
INTENSIFY SLOWLY THROUGH TAU 36 AS MODERATE VWS PERSISTS. AFTER TAU
36, EASING SHEAR WILL ALLOW TS 27W TO RAPIDLY INTENSIFY TO A PEAK
OF 110 KTS BY TAU 72. BY TAU 120, THE SYSTEM WILL WEAKEN SLIGHTLY
DUE TO LOWER OHC. TS 27W HAS A COMPACT CIRCULATION AND IS PRONE TO
SIGNIFICANT FLUCTUATIONS IN INTENSITY. IF THE VWS EASES SOONER AND
TS 27W DEVELOPS A COHERENT INNER CORE MORE QUICKLY, THEN RAPID
INTENSIFICATION (RI) COULD COMMENCE EARLIER AND LEAD TO A HIGHER
PEAK INTENSITY THAN FORECAST.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
60 BUT DIVERGES SIGNIFICANTLY BY TAU 96 AND TAU 120. THE
CROSS-TRACK SPREAD INCREASES FROM 160 NM AT TAU 60 TO 500 NM AT TAU
120. THE DYNAMICAL MODELS OCCUPY THE POLEWARD HALF OF THE GUIDANCE
ENVELOPE, WITH NAVGEM, GALWEM, AND HAFS-A AS THE MOST POLEWARD
SOLUTIONS. THE AI MODELS LEAN EQUATORWARD, WITH AIGFS AND THE
AI-GEFS MEAN TRACKS AS THE MOST EQUATORWARD. THE GOOGLE DEEPMIND
SOLUTION LIES NORTH OF THESE SOLUTIONS BUT SOUTH OF THE MULTI-MODEL
CONSENSUS (CONW). THE JTWC FORECAST TRACK IS POSITIONED USING A
BLEND OF CONW AND THE MEAN OF THE AI MODELS, PLACING IT NEAR THE
ECMWF AND JGSM SOLUTIONS AND SLIGHTLY NORTH OF DEEPMIND. RI AIDS
CONTINUE TO TRIGGER THIS CYCLE, AND HAFS-A DEPICTS IMMEDIATE RI,
PEAKING AT 125 KTS BY TAU 72. GIVEN THE CURRENT SATELLITE
PRESENTATION, THESE SOLUTIONS ARE DISCOUNTED. GFS AND DEEPMIND ARE
MORE CONSERVATIVE INITIALLY AND DEPICT STEADY TO RAPID
INTENSIFICATION BEGINNING NEAR TAU 36. THE JTWC INTENSITY FORECAST
LEANS CLOSER TO THESE SOLUTIONS, CALLING FOR DELAYED RI BETWEEN TAU
24 AND TAU 72.

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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