WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (NAKRI) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.8N 133.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 331 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W CONTINUES TO STRUGGLE TO CONSOLIDATE DUE TO
PERSISTENT VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. THE SYSTEM
IS CURRENTLY POSITIONED JUST SOUTH OF AN UPPER-LEVEL ANTICYCLONE
UNDER EASTERLY TO NORTHEASTERLY FLOW ALOFT. ANIMATED ENHANCED 
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A WELL-DEFINED EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC), WITH A CLUSTER OF DEEP 
CONVECTION FLARING OVER THE SOUTHWEST QUADRANT. A 091904Z GMI 37GHZ
COLOR COMPOSITE MICROWAVE IMAGE REVEALS FRAGMENTED SHALLOW
CONVECTIVE BANDING WRAPPING INTO A DEFINED LLCC, WITH DISORGANIZED
CONVECTION SHEARED TO THE SOUTH. SURFACE OBSERVATIONS FROM KITA-
DAITO, APPROXIMATELY 140NM WEST OF THE CENTER, INDICATE NORTH-
NORTHEASTERLY WINDS AT 18 KNOTS. OTHER THAN THE DRY AIR ENTRAINMENT, 
ENVIRONMENTAL CONDITIONS HAVE IMPROVED SLIGHTLY, WITH LOW (10-15 
KNOTS) VERTICAL WIND SHEAR (VWS), WHICH HAS DECREASED SLIGHTLY OVER 
THE PAST DAY, WITH WARM (28C) SST VALUES. THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON THE EIR SATELLITE IMAGERY. THE 
INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
RECENT ASCAT AND THE LOWER RANGE OF AGENCY DVORAK ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE 
(STR), WITH A WEAK RIDGE EXTENSION TO THE NORTH.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 091651Z
   CIMSS ADT: 37 KTS AT 091730Z
   CIMSS AIDT: 40 KTS AT 091730Z
   CIMSS D-MINT: 30 KTS AT 091651Z
   CIMSS D-PRINT: 27 KTS AT 091730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TS 29W IS FINALLY BEGINNING TO TURN 
NORTHWESTWARD BASED ON THE MOST RECENT EIR SATELLITE IMAGERY FROM
091800-2010Z. THE SYSTEM SHOULD CONTINUE TO TRACK GENERALLY
NORTHWESTWARD THROUGH TAU 24 UNDER THE STEERING INFLUENCE OF THE
STR EXTENSION TO THE NORTH. SLOW DEVELOPMENT IS EXPECTED THROUGH
TAU 24 DUE TO THE PERSISTENT DRY AIR ENTRAINMENT. AFTER TAU 24, THE
SYSTEM IS FORECAST TO TURN NORTHWARD TO NORTHEASTWARD AS IT ROUNDS
THE STR AXIS. THE SYSTEM IS EXPECTED TO MOISTEN AND CONSOLIDATE,
WITH IMPROVING POLEWARD OUTFLOW INTO THE MIDLATITUDE WESTERLIES FROM 
TAU 36 TO TAU 72. CONSEQUENTLY, TS 29W WILL INTENSIFY AT A FASTER 
RATE WITH INCREASING POTENTIAL FOR A SHORT PERIOD OF NEAR-RAPID 
INTENSIFICATION. A PEAK INTENSITY OF 80-85 KNOTS IS ANTICIPATED NEAR 
TAU 72. AFTER TAU 72, TS 29W WILL BEGIN TO INTERACT WITH THE 
MIDLATITUDE WESTERLIES AND ACCELERATE EAST-NORTHEASTWARD TO EASTWARD, 
WITH STEADY WEAKENING DUE TO INCREASING VERTICAL WIND SHEAR (25-40 
KNOTS). EXTRA-TROPICAL TRANSITION (ETT) WILL COMMENCE BY TAU 96, WITH 
ETT COMPLETE BY TAU 120 AS THE SYSTEM GAINS FRONTAL CHARACTERISTICS 
AND BECOMES EMBEDDED WITHIN STRONG MIDLATITUDE WESTERLY FLOW.  

MODEL DISCUSSION: THE TIMING OF THE SHARP RECURVATURE REMAINS 
UNCERTAIN WITH THE 091200Z GEFS AND EPS RUNS SHOWING A WIDE SPREAD
OF SOLUTIONS FROM JUST EAST OF OKINAWA TO 133E. IN GENERAL,
DETERMINISTIC AND PROBABILISTIC GUIDANCE HAS COME INTO BETTER
AGREEMENT OVER THE PAST DAY IN THE EARLY PHASE OF THE FORECAST
TRACK. AFTER TAU 48, GUIDANCE IS IN GOOD AGREEMENT WITH A 50-65NM
CROSS-TRACK SPREAD FROM TAU 48 TO TAU 72. ALL GEFS AND EPS ENSEMBLE
SOLUTIONS REMAIN WELL SOUTH OF THE KANTO PLAIN DURING THIS PERIOD.
THE HAFS-A DEPICTS A FAIRLY COMPACT WINDFIELD WITH GALE-FORCE WINDS
WELL SOUTH OF THE KANTO PLAIN AND MAXIMUM WINDS ALONG THE SOUTHERN
QUADRANT OF THE SYSTEM. AS THE SYSTEM ACCELERATES EASTWARD AFTER
TAU 72, GUIDANCE DIVERGES ALONG TRACK WITH INCREASING UNCERTAINTY.
HAFS-A AND COAMPS-TC (GFS) BOTH SUPPORT THE NEAR-RI INTENSIFICATION
PHASE, WITH HAFS-A PEAKING THE INTENSITY AT 71 KNOTS AND COAMPS-TC
AT 82 KNOTS NEAR TAU 72.      

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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