WDPN31 PGTW 202100

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//

SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (DUJUAN) WARNING

NR 022//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 31.3N 137.9E

   INITIAL INTENSITY: 60 KTS

   GEOGRAPHIC REFERENCE: 256 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN

   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS

   SIGNIFICANT WAVE HEIGHT: 28 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS

TROPICAL STORM 24W (DUJUAN) WITH AN IMPROVING CONVECTIVE STRUCTURE

INDICATED BY A SYMMETRIZING CENTRAL DENSE OVERCAST (CDO) FEATURE

AND COOLING CLOUD TOP TEMPERATURES. RIGHT AROUND 201800Z, A DIMPLE

EYE ATTEMPTED TO FORM, FURTHER SUGGESTING THAT THE SYSTEM MAY BE

ORGANIZING. A 201507Z GMI 37 GHZ MICROWAVE IMAGE REVEALED A DEFINED

MICROWAVE EYE WITH A WEAKNESS IN THE SOUTHERN SEMICIRCLE. THE

CORRESPONDING 89 GHZ VERSION OF THE SAME PASS SHOWED THAT THE

UPPER-LEVEL CENTER IS DISPLACED SLIGHTLY TO THE NORTH OF THE

LOW-LEVEL CENTER, INDICATIVE OF A NORTHWARD VORTEX TILT WITH

HEIGHT. THE VORTEX TILT IS LIKELY IN RESPONSE TO INCREASING

SOUTHERLY VERTICAL WIND SHEAR ACTING ON THE SYSTEM. THE INITIAL

POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED

EIR IMAGERY AND EXTRAPOLATION FROM THE GMI IMAGE.  THE INITIAL

INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON

THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW.

ENVIRONMENTAL ANALYSIS INDICATES THAT 24W IS IN A MARGINALLY

FAVORABLE ENVIRONMENT CHARACTERIZED BY ROBUST OUTFLOW ALOFT, LOW

TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT

FROM THE WEST, AND WARM (28-29 C) SEA SURFACE TEMPERATURES.



INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK



CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OF A SUBTROPICAL

RIDGE (STR) CENTERED EAST-SOUTHEAST OF JAPAN



AGENCY DVORAK AND AUTOMATED FIXES:

   PGTW: T3.5 - 55 KTS

   RJTD: T4.5 - 77 KTS

   RCTP: T4.0 - 65 KTS

   CIMSS SATCON: 65 KTS AT 201702Z

   CIMSS ADT: 54 KTS AT 201800Z

   CIMSS AIDT: 53 KTS AT 201800Z

   CIMSS D-MINT: 73 KTS AT 201704Z

   CIMSS D-PRINT: 70 KTS AT 201800Z



FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE

   VWS: 15-20 KTS

   SST: 28-29 CELSIUS

   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

   OTHER FACTORS: DRY AIR ENTRAINMENT



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 24W IS FORECAST TO CONTINUE ROUNDING

THE AXIS OF THE STEERING RIDGE THROUGH TAU 24 WITH AN INCREASING

EASTWARD COMPONENT TO THE TRAJECTORY. THE CPA TO YOKOSUKA IS

EXPECTED TO OCCUR JUST AFTER TAU 12, AND REMAINS CONSISTENT WITH

THE PREVIOUS FORECAST. FOLLOWING TAU 24, TRACK SPEEDS WILL BEGIN

TO INCREASE AS 24W TRAVERSES THE NORTHERN EXTENT OF THE STR AND

STARTS TO INTERACT WITH THE STRONG MID-LATITUDE WESTERLIES.

EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 48 WITH

COMPLETION BY TAU 60, ONCE THE SYSTEM BECOMES FURTHER EMBEDDED

UNDER THE UPPER-LEVEL JET AND THERMAL ADVECTION INCREASES. IN

TERMS OF INTENSITY, 24W IS FORECAST TO MARGINALLY INTENSIFY OVER

THE NEXT 24 HOURS TO A PEAK INTENSITY OF AROUND 70 KTS. THIS

INTENSIFICATION IS DUE PRIMARILY TO THE SYSTEM TAPPING INTO AN

EXCEPTIONAL POLEWARD OUTFLOW CHANNEL, SUPPORTED BY A STRONG

150+ KNOT JET MAXIMUM SITUATED NORTHEAST OF HOKKAIDO. AFTER TAU

24, WESTERLY VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT WILL

DRAMATICALLY INCREASE. ADDITIONALLY, SEA SURFACE TEMPERATURES WILL

DROP AFTER 24W CLEARS THE KUROSHIO CURRENT. AS A RESULT, 24W WILL

WEAKEN AS IT TRANSITIONS INTO A COLD-CORE CYCLONE.



MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN VERY GOOD

AGREEMENT WITH A CROSS-TRACK SPREAD OF ONLY 30 NM AT TAU 24.

AFTER TAU 24, MODELS SLIGHTLY DIVERGE, MOSTLY IN THE ALONG-TRACK

DIRECTION. AT TAU 60, THE ALONG-TRACK SPREAD IS MEASURED TO BE

ABOUT 220 NM WITH GFS BEING THE SLOWEST MODEL AND THE EC-AIFS AS

THE FASTEST. OVERALL, THE JTWC TRACK FORECAST IS PLACED NEAR THE

MULTI-MODEL CONSENSUS THROUGH TAU 36 AND THEN SLIGHTLY FASTER

THROUGH TAU 60 WITH HIGH CONFIDENCE. INTENSITY GUIDANCE CLOSELY

AGREES ON MARGINAL INTENSIFICATION THROUGH TAU 24 FOLLOWED BY

WEAKENING WITH NO NOTABLE OUTLIERS PRESENT. THEREFORE, THE JTWC

INTENSITY FORECAST IS SET CLOSE TO THE CONSENSUS WITH HIGH

CONFIDENCE.



FORECAST CONFIDENCE:

   TRACK 00-72 HR: HIGH

   INTENSITY 00-72 HR: HIGH//

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