Advisories

WDPN33 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 27W (KOGUMA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4N 166.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 354 NM SOUTH OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 27W HAS CHANGED LITTLE IN ORGANIZATION OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A SMALL, RAGGED CENTRAL DENSE OVERCAST (CDO) DISPLACED TO
THE NORTHWEST OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC). CONVECTION REMAINS NOTABLY ABSENT ALONG THE SOUTHERN
PERIPHERY OF THE CIRCULATION. A PARTIAL 052305Z ASCAT-C PASS
CONFIRMED THE PRESENCE OF GALE-FORCE WINDS AND AN ASYMMETRIC WIND
FIELD, BUT LIKELY DID NOT SAMPLE THE STRONGEST WINDS NEAR THE LLCC.
TS 27W IS LOCATED IN A MARGINALLY FAVORABLE ENVIRONMENT, WITH VERY
WARM SEA SURFACE TEMPERATURES (SST) NEAR 30 DEGREES CELSIUS OFFSET
BY MODERATE EASTERLY VERTICAL WIND SHEAR (VWS) AND DRY AIR WRAPPING
INTO THE CIRCULATION FROM THE SOUTHWEST. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A TIGHT CLUSTER OF SATELLITE
FIXES FROM PGTW, PHFO, AND RCTP. THE INITIAL INTENSITY HAS BEEN
HELD AT 45 KTS WITH MEDIUM CONFIDENCE, BASED ON THE NEARLY
UNCHANGED DVORAK CLASSIFICATIONS AND OBJECTIVE ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN EXTENSION OF A MID-LEVEL
SUBTROPICAL RIDGE 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 SATCON: 43 KTS AT 060209Z
   CIMSS ADT: 51 KTS AT 060230Z
   CIMSS AIDT: 40 KTS AT 060230Z
   CIMSS D-MINT: 44 KTS AT 060209Z
   CIMSS D-PRINT: 42 KTS AT 060510Z

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: THE JTWC FORECAST TRACK HAS SHIFTED
SOUTHWARD BY NEAR 45 NM AT TAU 120.

FORECAST DISCUSSION: TS 27W IS TRAVELING NORTHWESTWARD ALONG THE
SOUTHWESTERN FLANK OF AN EXTENSION OF THE STR CENTERED FAR TO THE
NORTH. THIS RIDGE WILL BUILD WESTWARD OVER THE NEXT 24 HOURS AND
INDUCE A TURN TOWARD THE WEST-NORTHWEST. NEAR THE END OF THE
FORECAST PERIOD, A SHORTWAVE TROUGH EJECTING OFF THE COAST OF
HONSHU WILL CREATE A WEAKNESS IN THE STR, ALLOWING THE SYSTEM TO
TURN NORTHWESTWARD AND GAIN MORE LATITUDE. SIGNIFICANT UNCERTAINTY
EXISTS REGARDING THE DEGREE OF THE TURN DUE TO INTERACTION AMONG
THE TROUGH, STR, AND TYPHOON (TY) 15E TO THE NORTH. A MORE RAPID
PROGRESSION OF THE TROUGH AND TY 15E WOULD ENABLE THE STR TO
REBUILD MORE QUICKLY, THEREBY CLOSING OFF THE WEAKNESS AND RESULT
IN A MORE WESTWARD TRAJECTORY AT TAU 96 AND TAU 120. MODERATE VWS
WILL PERSIST OVER THE NEXT 24 HOURS, THEN EASE FOR THE REMAINDER OF
THE FORECAST PERIOD. THE SHEAR, COUPLED WITH DRY AIR WRAPPING INTO
THE CIRCULATION FROM THE SOUTHWEST, WILL CONTINUE TO SLOW
DEVELOPMENT THROUGH TAU 12. THEREAFTER, AS THE SYSTEM BECOMES
BETTER ORGANIZED, A FASTER RATE OF INTENSIFICATION WILL COMMENCE.
IT IS CONCEIVABLE THAT, IF TS 27W CAN QUICKLY ACHIEVE
AXISYMMETRIZATION AND IF CONVECTION CAN BUILD OVER THE LLCC AND
HOLD, RAPID INTENSIFICATION (RI) COULD OCCUR, LEADING TO AN EARLIER
AND HIGHER PEAK INTENSITY THAN CURRENTLY FORECAST. TS 27W IS
COMPACT, SO SIGNIFICANT FLUCTUATIONS IN INTENSITY ARE CERTAINLY
POSSIBLE. TOWARD TAU 120, LOWER OCEAN HEAT CONTENT WILL LEAD TO
SLIGHT WEAKENING.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IN GOOD
AGREEMENT, WITH CROSS-TRACK SPREAD INCREASING FROM 75 NM AT TAU 24
TO 210 NM AT TAU 72. NAVGEM, GALWEM, AND HAFS-A LINE THE POLEWARD
EDGE OF THE GUIDANCE ENVELOPE, WHILE THE AI MODELS OCCUPY THE
EQUATORWARD SIDE. OVER THE PAST THREE CYCLES, THE OVERALL GUIDANCE
ENVELOPE HAS SHIFTED EQUATORWARD. AS A RESULT, THE JTWC FORECAST
TRACK HAS BEEN NUDGED EQUATORWARD AND REPRESENTS A BLEND OF THE
MULTI-MODEL CONSENSUS AND THE MEAN OF THE AI MODELS AND LIES
CLOSEST TO THE ECMWF TRACK SOLUTION. GOOGLE DEEPMIND IS SLIGHTLY
SOUTH OF THE JTWC FORECAST TRACK. SIGNIFICANT SPREAD EXISTS AMONG
THE INTENSITY GUIDANCE. MULTIPLE RI AIDS HAVE TRIGGERED. FOR NOW,
THESE ARE DISCOUNTED FOR AN IMMEDIATE RI SCENARIO GIVEN RECENT
SATELLITE TRENDS. HAFS-A IS THE MOST AGGRESSIVE SOLUTION IN THE
NEAR TERM, DEPICTING IMMEDIATE RI TO 110 KTS BY TAU 60. DEEPMIND,
ON THE OTHER HAND, HOLDS THE INTENSITY STEADY THROUGH TAU 36 BEFORE
DEPICTING STEADY TO RAPID INTENSIFICATION TO A PEAK OF 115 KTS BY
TAU 96. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE INTENSITY
CONSENSUS WITH MEDIUM CONFIDENCE. IT IS LESS AGGRESSIVE THAN HAFS-A
AND THE RI AIDS BUT CALLS FOR EARLIER INTENSIFICATION THAN
DEEPMIND.

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