505 

WDPN31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR
038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.3N 146.8E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 314 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC), WITH A SMALL POCKET OF REMNANT
CONVECTION IN THE SOUTHEASTERN QUADRANT OF THE CIRCULATION. TO THE
NORTHEAST, A LOW-LEVEL ROPE CLOUD INDICATES THE WESTERN EXTENT OF A
COLD FRONTAL BOUNDARY, POSITIONED OVER MINAMAI TORI SHIMA. ALONG THE
WESTERN FLANK OF THE CIRCULATION, A FIELD OF LOW-LEVEL STRATIFORM
CLOUDS DELINEATES AN AREA OF SUBSIDENCE AND DRY, STABLE AIR, WHILE
GRAVITY WAVES PROPAGATING WESTWARD FROM THE CONVECTIVE CORE ARE
EVIDENT MOVING OVER THE LOW-LEVEL CLOUD FIELDS. PRONOUNCED DRY MID-
LEVEL AIR ENTRAINMENT, ACCOMPANIED BY MODERATE WESTERLY SHEAR, HAS
DISPLACED CONVECTION TO THE EAST, FULLY EXPOSING THE LLCC. THE CLEAR
DEFINITION OF THE LLCC LENDS HIGH CONFIDENCE TO THE INITIAL POSITION.
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE AT 60 KNOTS.
THIS IS CONSIDERABLY HIGHER THAN THE CIMSS ADT-AIDT ESTIMATES, BUT IS
CONSISTENT WITH THE CIMSS DPRINT, DMINT, SATCON AND THE BULK OF THE
AGENCY DVORAK CURRENT INTENSITY ESTIMATES. EARLIER ASCAT AND SAR
DATA SUPPORTED AN INTENSITY HIGHER THAN MOST OF THE FIX ESTIMATES.
ENVIRONMENTAL CONDITIONS ARE CONTINUING TO DETERIORATE, WITH
MODERATE AND INCREASING WESTERLY SHEAR, COOL SSTS (NOW BELOW 26C),
AND DRY MID-LEVEL AIR ENTRAINMENT. WHILE POLEWARD OUTFLOW REMAINS
ROBUST, IT IS INSUFFICIENT TO COMPENSATE FOR THE STRONG WESTERLY
SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA.

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 62 KTS AT 180600Z
   CIMSS ADT: 43 KTS AT 180540Z
   CIMSS AIDT: 38 KTS AT 180540Z
   CIMSS D-MINT: 66 KTS AT 180555Z
   CIMSS D-PRINT: 63 KTS AT 180600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: A WEDGE OF DRY MID-LEVEL AIR SITUATED ALONG THE
WESTERN FLANK OF THE SYSTEM.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 04W (SINLAKU) HAS TRACKED
NORTH-NORTHEASTWARD OVER THE PAST 12 HOURS, ALONG THE WESTERN FLANK
OF A LARGE STR TO THE EAST. FORWARD SPEED MODERATED SLIGHTLY AS A
TRANSIENT MID-LATITUDE ANTICYCLONE TRANSITED EAST OF JAPAN AND PASSED
NORTH OF THE SYSTEM. AS THE ANTICYCLONE MOVES TO THE NORTHEAST, THE
STR IS EXPECTED TO RESUME DOMINANCE AS THE PRIMARY STEERING
INFLUENCE. OVER THE NEXT 48 HOURS, THE STR WILL REGENERATE
SOUTHWESTWARD TOWARD GUAM. SIMULTANEOUSLY, THE REMNANT FRONTAL
BOUNDARY TO THE NORTHEAST WILL LIFT NORTHWARD WHILE MAINTAINING A
ZONAL ORIENTATION. THESE FEATURES WILL COLLECTIVELY INDUCE A RAPID
RECURVATURE, TRANSITIONING TS 04W TO A DUE EASTWARD TRAJECTORY ALONG
THE FRONTAL INTERFACE BY TAU 48. STEADY DECAY IS ANTICIPATED OVER THE
NEXT 24 TO 36 HOURS DUE TO THE CUMULATIVE EFFECTS OF MODERATE TO
STRONG VWS, DRY AIR ENTRAINMENT, AND THERMODYNAMIC LIMITATIONS FROM
MARGINAL SSTS. DURING THE LATER TAUS, AS TS 04W COMPLETES EXTRA-
TROPICAL TRANSITION (ETT), BAROCLINIC FORCING WILL SUSTAIN WINDS OF
45-50 KNOTS.

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT AGREEMENT ALONG THE
CROSS-TRACK PLANE, WITH MODEL SPREAD CONSTRAINED TO 90NM BY TAU 48.
ALONG-TRACK UNCERTAINTY IS SLIGHTLY HIGHER (160NM SPREAD). GFS-
INITIALIZED AI-DRIVEN MODELS REMAIN THE POLEWARD AND FASTEST
OUTLIERS, WHILE EGRR IS THE EQUATORWARD AND SLOWEST EXTREME. THE JTWC
FORECAST IS ALIGNED WITH THE AI-CONSENSUS AND EXPERIMENTAL AI
TRACKERS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE EXHIBITS GREATER
DIVERGENCE; GFS, HAFS-A, AND HWRF SUGGEST A GRADUAL WEAKENING TREND,
WHEREAS SHIPS (GFS AND NAVGEM) DEPICT RAPID DISSIPATION. THE JTWC
FORECAST FAVORS THE HWRF-HAFS SOLUTIONS WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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