Advisories

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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