Advisories

WDPN31 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 
024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.6N 133.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 346 NM SOUTHEAST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SURIGAE HAS UNDERGONE REMARKABLY RAPID DETERIORATION OVER THE PAST
30 HOURS, WEAKENING FROM A 130-KT SUPER TYPHOON (STY) AT 271800Z TO
A 55-KT TROPICAL STORM (TS) AT 290000Z. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED LOW-LEVEL
CIRCULATION CENTER, WITH SHALLOW CONVECTION FLARING ALONG THE OUTER
PERIPHERY OF THE COMPACT CIRCULATION. THE REMAINING DEEP CONVECTION
HAS BEEN SHEARED 100 NM SOUTHEAST OF THE LLCC. THIS EXTREMELY RAPID
WEAKENING TREND IS LARGELY THE RESULT OF VERY STRONG NORTHERLY
VERTICAL WIND SHEAR (VWS) OF 25-35 KTS, WHICH PREVENTS CONVECTION
FROM BEING SUSTAINED OVER THE LLCC AND CONTINUES TO ADVECT DRY AIR
INTO THE CIRCULATION. THESE FACTORS OUTWEIGH THE DEVELOPMENTAL
BENEFITS OF WARM SEA SURFACE TEMPERATURES (SST) AND CONSTITUTE A
HIGHLY UNFAVORABLE ENVIRONMENT. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE VERY WELL-DEFINED, EXPOSED LLCC IN
MSI. A 282056Z RCM-1 SAR PASS INDICATED PEAK WINDS OF 48 KTS. THE
INITIAL INTENSITY HAS BEEN LOWERED TO 55 KTS WITH LOW CONFIDENCE,
GIVEN THE TENDENCY OF SAR-DERIVED WINDS TO UNDERESTIMATE PEAK WIND
SPEEDS AT HIGH INCIDENCE ANGLES AND THE LARGE SPREAD AMONG THE
SUBJECTIVE AND OBJECTIVE ESTIMATES.

INITIAL WIND RADII BASIS: SAR DATA

CURRENT STEERING MECHANISM: NORTHWESTERN FLANK OF A SUBTROPICAL
RIDGE (STR) CENTERED EAST-SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS ADT: 55 KTS AT 282340Z
   CIMSS AIDT: 54 KTS AT 282340Z
   CIMSS D-MINT: 41 KTS AT 281925Z
   CIMSS D-PRINT: 33 KTS AT 282340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 25-35 KTS
   SST: 27-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 25W WILL MAINTAIN A STEADY NORTHEASTWARD
MOTION OF 8-10 KTS THROUGH TAU 36, STEERED ALONG THE NORTHWESTERN
PERIPHERY OF A STR CENTERED NEAR 32N 157E. THEREAFTER, THE SYSTEM
WILL ACCELERATE NORTHEASTWARD AS IT BECOMES EMBEDDED WITHIN
STRONGER DEEP-LAYER WESTERLY FLOW. A 135-KT JET STREAM POSITIONED
OVER THE SEA OF JAPAN WILL LIFT NORTHWARD OVER THE NEXT 12 HOURS.
THEREFORE, THE VWS RESPONSIBLE FOR THE EXTREMELY RAPID WEAKENING
TREND WILL EASE TO 20-25 KTS OVER THE NEXT 12 HOURS, ALLOWING
LIMITED CONVECTION TO REBUILD OVER THE EASTERN PERIPHERY OF THE
CIRCULATION. THIS DEVELOPMENT WILL REDUCE THE RATE OF WEAKENING,
RESULTING IN A STEADY 40-KT INTENSITY FROM TAU 24 TO TAU 48. AS TS
25W CONTINUES TO GAIN LATITUDE, THERMAL ADVECTION WILL INCREASE.
THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION NEAR TAU 36, WITH
TRANSITION COMPLETING BY TAU 60. AT THE END OF THE FORECAST PERIOD,
THE EXTRATROPICAL CYCLONE WILL REINTENSIFY AS IT PHASES WITH A DEEP
TROUGH PASSING OVER NORTHERN HONSHU.

MODEL DISCUSSION: THE CROSS-TRACK SPREAD IN THE TRACK GUIDANCE
REMAINS SMALL, HOLDING NEAR 50 NM FROM TAU 24 TO TAU 48. THE
ALONG-TRACK SPREAD IS STILL RATHER LARGE, INCREASING FROM 80 NM AT
TAU 24 TO 110 NM AT TAU 48 AMONG THE RELIABLE TRACK SOLUTIONS. THE
JTWC TRACK FORECAST HAS CHANGED LITTLE AND CONTINUES TO REFLECT A
BLEND OF THE JTWC CONSENSUS (CONW) AND THE AI-MODEL MEAN. NOTABLY,
GOOGLE DEEPMIND, ECMWF, AND NAVGEM ARE THE FASTEST TRACK SOLUTIONS.
THE SPREAD AMONG THE INTENSITY AIDS HAS INCREASED THIS CYCLE,
LIKELY ATTRIBUTABLE TO THE SYSTEMS CONTINUED RAPID WEAKENING THAT
EXCEEDED MODEL PROJECTIONS FROM THE PREVIOUS CYCLE. IN FACT, THE
STATISTICAL-DYNAMICAL SHIPS GUIDANCE DISSIPATES THE STORM BY TAU
48. HAFS-A HAS TRENDED WEAKER AND IS NOW IN CLOSE ALIGNMENT WITH
DEEPMIND. CONSEQUENTLY, THE JTWC INTENSITY FORECAST HAS BEEN NUDGED
LOWER THROUGH THE EARLY FORECAST TAUS BUT IS HELD SLIGHTLY HIGHER
THAN THE CONSENSUS. GFS, HAFS-A, AND ECMWF DEPICT SLIGHT
REINTENSIFICATION NEAR TAU 60 DUE TO INCREASING BAROCLINIC FORCING.

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