Advisories

WDPN31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (DUJUAN) WARNING NR 
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.1N 144.5E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 175 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 24W AS A COMMA-SHAPED SYSTEM WITH A WELL-DEFINED CENTRAL
DENSE OVERCAST AND A THICK TAIL WRAPPING AROUND THE NORTHERN
PERIPHERY. A 172039Z WSF-M MWI PASS REVEALED A LOWER-LEVEL EYE
FEATURE IN THE 37 GHZ IMAGE, DISPLACED FROM THE 89 GHZ CONVECTIVE
SIGNATURE, INDICATING A SLIGHT POLEWARD TILT IN THE VORTEX WITH
HEIGHT. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, CHARACTERIZED BY
LIGHT TO MODERATE, SOUTHERLY VERTICAL WIND SHEAR (VWS), WARM SEA
SURFACE TEMPERATURES (SST) OF 28-29 DEGREES CELSIUS, AND GOOD
POLEWARD OUTFLOW ALOFT. A TIMELY 172353Z ASCAT-B IMAGE SAMPLED
ASYMMETRICALLY DISTRIBUTED WINDS OF NEAR 50 KTS NEAR THE CENTER,
INDICATING A WEAKENING OF THE CORE WIND FIELD. THE INITIAL POSITION
IS PLACED SLIGHTLY SOUTH OF THE MID-LEVEL ROTATION WITH MEDIUM
CONFIDENCE. GIVEN THAT THE SCATTEROMETER DATA MAY NOT BE RESOLVING
THE HIGHEST WINDS NEAR THE COMPACT CORE, THE INITIAL INTENSITY IS
CONSERVATIVELY LOWERED TO 60 KTS WITH MEDIUM CONFIDENCE, WHICH IS
SUPPORTED BY A BLEND OF THE T3.0-4.0 DVORAK CLASSIFICATIONS. THIS
ASSESSMENT REMAINS HIGHER THAN THE OBJECTIVE ESTIMATES FROM CIMSS,
WHICH MAY BE UNDERREPRESENTING THE COMPACT INNER-CORE INTENSITY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A SUBTROPICAL
RIDGE (STR) WELL EAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 60 KTS AT 171630Z
   CIMSS ADT: 55 KTS AT 172330Z
   CIMSS AIDT: 51 KTS AT 172330Z
   CIMSS D-MINT: 51 KTS AT 172322Z
   CIMSS D-PRINT: 45 KTS AT 172330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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: THE FORWARD MOTION OF TS 24W HAS SLOWED AS IT
TURNS WESTWARD IN RESPONSE TO A STR BUILDING WESTWARD FROM THE
NORTHEAST. THIS WEST-NORTHWESTWARD TRAJECTORY WILL CONTINUE FOR THE
NEXT 24 HOURS, BEFORE THE SYSTEM TURNS POLEWARD AND ROUNDS THE
WESTERN PERIPHERY OF THE STR. BY TAU 60, THE SYSTEM WILL ACCELERATE
TOWARD THE NORTHEAST UNDER THE STEERING INFLUENCE OF DEEP-LAYER
MID-LATITUDE WESTERLY FLOW. THE RECENT WEAKENING OF TS 24W WAS
LIKELY THE RESULT OF A COMBINATION OF SOUTHERLY SHEAR AND A
BROADENING INNER CORE STRUCTURE. FAVORABLE ENVIRONMENTAL
CONDITIONS, INCLUDING WARM SST, LOW TO MODERATE VWS, AND MODEST
POLEWARD OUTFLOW, WILL PERSIST THROUGH TAU 24, SUPPORTING A
NEAR-STEADY INTENSITY. AFTER TAU 24, THE SYSTEM WILL GAIN ACCESS TO
A POLEWARD OUTFLOW CHANNEL. HOWEVER, AS THE CORE WIND FIELD
BROADENS, THE SYSTEM IS UNLIKELY TO REDEVELOP A COMPACT INNER CORE.
AS SUCH, THE FORECAST CALLS FOR ONLY MODEST INTENSIFICATION TO 65
KTS. BY TAU 72, VWS WILL INCREASE, AND WEAKENING WILL COMMENCE. THE
STORM WILL BECOME SUBJECT TO BAROCLINIC FORCING BEYOND TAU 72,
WHICH WILL OFFSET THE WEAKENING INDUCED BY INCREASING VWS.
EXTRATROPICAL TRANSITION WILL COMPLETE BY TAU 120.

MODEL DISCUSSION: THE TRACK GUIDANCE SUITE REMAINS IN GOOD
AGREEMENT, EXHIBITING A CROSS-TRACK SPREAD OF 100 NM AT TAU 72.
RELATIVE TO THE PREVIOUS FORECAST CYCLE, THE GUIDANCE HAS SHIFTED
EASTWARD FROM TAU 48 TO TAU 120. AS A RESULT, THE JTWC FORECAST
TRACK HAS ALSO SHIFTED EASTWARD AND FARTHER OFFSHORE OF THE KANTO
PLAIN. THIS SHIFT TAKES THE ENTIRE STORM-FORCE WIND FIELD OUT TO
SEA. THE AI MODELS CONTINUE TO FAVOR THE WESTERN SIDE OF THE
GUIDANCE ENVELOPE. THE JTWC FORECAST TRACK IS PLACED NEAR THE
MULTI-MODEL CONSENSUS (CONW), WHICH LIES EAST OF THE EXPERIMENTAL
GOOGLE DEEPMIND SOLUTION, THROUGH TAU 96. AT TAU 120, THE FORECAST
HEDGES CLOSER TO GFS AND ECMWF. THE JTWC INTENSITY FORECAST IS SET
NEAR THE CONSENSUS WITH MEDIUM CONFIDENCE. THE CONSENSUS GENERALLY
DEPICTS A STEADY INTENSITY THROUGH TAU 24, FOLLOWED BY A SLIGHT
INCREASE IN INTENSITY FROM TAU 24 TO TAU 60, AND GRADUAL WEAKENING
THEREAFTER. HAFS-A IS A NOTABLE, LOW-INTENSITY OUTLIER, DEPICTING
SIGNIFICANT DIFFICULTY IN RECOVERING INTENSITY DUE TO THE BROADER
CIRCULATION. THE DEEPMIND SOLUTION IS CLOSEST TO INTENSITY
CONSENSUS.

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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