Tropical Storm ROKE Advisory 9月29日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (ROKE)
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 23.9N 131.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 263 NM SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT, CONSOLIDATING SYSTEM WITH A CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 281725Z AMSR2
37GHZ COLOR COMPOSITE MICROWAVE IMAGE REVEALS A SMALL MICROWAVE EYE
FEATURE WITH A CYAN RING, WHICH TYPICALLY INDICATES IMMINENT RAPID
INTENSIFICATION (RI). ANIMATED WATER VAPOR IMAGERY DEPICTS ROBUST
POLEWARD OUTFLOW WITH TRANSVERSE BANDING ALONG THE WESTERN AND
NORTHERN SEMICIRCLES. ADDITIONALLY, LOW VERTICAL WIND SHEAR AND
WARM SST VALUES (28-29C) SUPPORT FURTHER INTENSIFICATION. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AMSR2
IMAGE. THE INITIAL INTENSITY OF 45 KTS IS HEDGED ABOVE THE DVORAK
INTENSITY ESTIMATES, WHICH ARE TOO LOW DUE TO THE COMPACT SYSTEM
SIZE. ADT ESTIMATES HAVE INCREASED STEADILY FROM 43 KNOTS AT
281740Z TO THE 281950Z ESTIMATE OF 49 KNOTS. THE ADT RAW T NUMBER
IS AT 3.6 (ABOUT 55 KNOTS).
INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK
CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   CIMSS ADT: 43 KTS AT 281740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: PEAK INTENSITY IS HIGHER AT 70 KNOTS
WITH INCREASING POTENTIAL FOR RAPID INTENSIFICATION OVER THE NEXT
36 HOURS.
FORECAST DISCUSSION: TS 20W IS A COMPACT SYSTEM WITH A CDO AND A
MICROWAVE EYE FEATURE AND APPEARS TO BE RAPIDLY CONSOLIDATING UNDER
HIGHLY FAVORABLE CONDITIONS INCLUDING ROBUST POLEWARD OUTFLOW.
THEREFORE, THE SYSTEM IS FORECAST TO INTENSIFY TO A PEAK OF 70
KNOTS WITHIN THE NEXT 36 HOURS AS IT ROUNDS THE STR AXIS. AFTER TAU
36, TS 20W SHOULD ENCOUNTER MIDLATITUDE WESTERLIES AS IT TRACKS
ALONG THE NORTHWESTERN PERIPHERY OF THE STR WITH CONVERGENCE ALOFT
LEADING TO A STEADY WEAKENING TREND THROUGH THE REMAINDER OF THE
FORECAST PERIOD. AFTER TAU 72, THE SYSTEM IS EXPECTED TO SLOW AND
STALL AS A LOW-LEVEL HIGH BUILDS TO THE NORTH AND NORTHEAST
EFFECTIVELY BLOCKING ANY FURTHER POLEWARD PROGRESSION. TS 20W WILL
WEAKEN SIGNIFICANTLY DUE TO THE UPPER-LEVEL CONVERGENCE AND
BAROCLINIC INTERACTION DURING THE EXTENDED PERIOD.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 48 WITH AN 110NM SPREAD IN SOLUTIONS. HOWEVER, THE
GUIDANCE DIVERGES QUICKLY WITH THE BULK OF THE GUIDANCE INDICATING
A QUASI-STATIONARY OR SLOW TRACK THROUGH TAU 120. SOME MODELS
INDICATE A FAST NORTHEASTWARD TRACK INCLUDING NAVGEM, AFUM, AEMN
AND UEMN. EXAMINATION OF NAVGEM FIELDS INDICATES A QUASI-STATIONARY
PHASE SOUTH-SOUTHEAST OF TOKYO, HOWEVER, THE VORTEX TRACKER IS
JUMPING ERRONEOUSLY NORTHEASTWARD TO OTHER DISTURBANCES. THE
281200Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) BOTH SHOW THE
LARGE MAJORITY OF SOLUTIONS STALLING THE SYSTEM SOUTH OF HONSHU;
VERY FEW SOLUTIONS INDICATE A RECURVE SCENARIO. THE TRACK
CONFIDENCE AFTER TAU 72 IS DUE PRIMARILY TO UNCERTAINTY IN THE
EXACT TRACK ONCE THE SYSTEM SLOWS AND STALLS. THE 281200Z COAMPS-TC
ENSEMBLE INDICATES A 60 TO 80 PERCENT PEAK PROBABILITY OF RI
THROUGH TAU 36 SUPPORTING THE JTWC INTENSITY FORECAST.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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