546 

WDPN31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 04W (SINLAKU) WARNING NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.3N 146.4E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 318 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN
INCREASINGLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) DECOUPLING
FROM THE MID-LEVEL CIRCULATION THAT IS BEING SHEARED AWAY TO THE
EAST. THERE IS NO LONGER ANY DEEP CONVECTION ASSOCIATED WITH THE
WEAKENING CYCLONE. ANIMATED WATER VAPOR IMAGERY CONTINUES TO
SHOWCASE ROBUST POLEWARD OUTFLOW AIDED BY THE PROXIMITY TO THE
MIDLATITUDE WESTERLIES NORTH OF THE SYSTEM, IN ADDITION TO
SIGNIFICANT DRY STABLE AIR BEING ENTRAINED FROM THE WEST. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 172311Z
METOP-B ASCAT THAT SHOWS THE WIND MINIMUM ASSOCIATED WITH THE
CENTER OF THE LLCC AND THE ANIMATED MSI THAT SHOWS THE PARTIALLY
EXPOSED LLCC. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A PARTIAL 171953Z RCM-1 SAR PASS THAT
CAPTURED A SWATH OF 60-65 KTS IN THE EASTERN SEMICIRCLE. THE
ENVIRONMENT IS CHARACTERIZED AS UNFAVORABLE WITH CONTINUED DRY AIR
ENTRAINMENT, MODERATE (20-25 KTS) WESTERLY VERTICAL WIND SHEAR
(VWS), AND COOLING (25-26 C) SEA SURFACE TEMPERATURES (SST).

INITIAL WIND RADII BASIS: SAR AND SCATTEROMETER DATA

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 51 KTS AT 180000Z
   CIMSS AIDT: 62 KTS AT 180000Z
   CIMSS D-PRINT: 69 KTS AT 180000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT

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: TYPHOON (TY) 04W (SINLAKU) HAS TAKEN A SLIGHT
NORTHWARD JOG OVER THE PAST 6 HOURS AS THE TRACK OF THE LLCC HAS
BEEN BRIEFLY MODULATED BY A STRONG TRANSIENT MIDLATITUDE SURFACE
HIGH TO THE NORTH. MEANWHILE, INCREASING WESTERLY VWS HAS DISPLACED
THE MID-LEVEL CIRCULATION TO THE EAST OF THE LLCC. ONCE THE
TRANSIENT HIGH EXITS THE AREA OF STEERING INFLUENCE AROUND TAU 24,
THE STR TO THE SOUTHEAST WILL ACCELERATE THE SYSTEM'S TRACK SPEED
IN AN INCREASINGLY EAST-NORTHEASTWARD DIRECTION FOR THE REMAINDER
OF THE FORECAST PERIOD. TY SINLAKU IS EXPECTED TO BEGIN
EXTRATROPICAL TRANSITION (ETT) AROUND TAU 36 AS IT TRANSITS OVER
MUCH COOLER (20-21 C) SEA SURFACE TEMPERATURES AND BECOMES EMBEDDED
IN THE MIDLATITUDE WESTERLIES. THE SYSTEM IS FORECAST TO CONTINUE
STEADILY WEAKENING THROUGH THE ENTIRE FORECAST PERIOD, DECREASING
TO 50 KTS AT TAU 48 UNDER THE INCREASINGLY HOSTILE ENVIRONMENTAL
CONDITIONS. IN SPITE OF THE WEAKENING TREND, 04W IS EXPECTED TO
MAINTAIN A BROAD AREA OF GALE-FORCE WINDS AS IT ACCELERATES INTO
THE NORTHERN PACIFIC AS AN EXTRATROPICAL CYCLONE.

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
ABOUT THE RECURVING TRACK OF 04W THROUGH THE NEXT 48 HOURS,
ALTHOUGH THE CROSS-TRACK SPREAD AT TAU 48 HAS INCREASED TO 90 NM.
NOTABLY, MOST OF THE AI MODEL GROUPING DEPICTS A FASTER TRACK SPEED
THAN THE PHYSICS-BASED MODELS, RESULTING IN AN ALONG-TRACK SPREAD
OF 130 NM AT TAU 48. THE JTWC TRACK FORECAST IS PLACED WITH HIGH
CONFIDENCE NEAR THE MODIFIED CONSENSUS THAT INCLUDES THE AI
SOLUTIONS. MODEL INTENSITY GUIDANCE IS IN GOOD AGREEMENT ABOUT THE
WEAKENING TREND THROUGH TAU 48, WITH THE EXCEPTION OF THE SHIPS
MODELS, WHICH DEPICT A MUCH FASTER RATE OF WEAKENING THAN THE
REMAINDER OF GUIDANCE. THE JTWC INTENSITY FORECAST IS PLACED
SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS AND CLOSE TO THE HAFS-A
SOLUTION WITH OVERALL HIGH CONFIDENCE.

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