WDPN31 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (NAKRI) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.5N 130.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 161 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W CONTINUES TO UNDERGO A COMPLEX INTERACTION
WITH A LOW- TO MID-LEVEL MESOVORTEX TO THE SOUTH WHICH CAN BE
TRACKED BACK 24 HOURS TO WHEN IT WAS MUCH MORE VERTICALLY ALIGNED
WITH THE LOW-LEVEL CIRCULATION CENTER (LLCC). AROUND 18 HOURS AGO,
THIS MID-LEVEL VORTEX DECOUPLED FROM THE LLCC WHICH CONTINUED TO
THE NORTHWEST, WHILE THE REMNANT MID-LEVEL ROTATION PUSHED OFF TO
THE WEST, LIKE TWO ICE SKATERS CIRCLING BACK TO ONE ANOTHER, THESE
TWO VORTICES ARE ABOUT TO MERGE ONCE AGAIN. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE LLCC ASSOCIATED WITH
TS 29W HAVING TURNED SOUTHWESTWARD OVER THE PAST SIX HOURS, BEING
PULLED IN TOWARDS THE MID-LEVEL VORTEX TO THE SOUTH. THE EIR LOOP
SHOWS STRONG CONVECTION AND INTENSE LIGHTNING ACTIVITY IN THE
VICINITY OF MINAMIDAITOJIMA ISLAND, AND RADAR DATA CONFIRMS THE
MID-LEVEL ROTATION CENTERED JUST TO THE NORTHWEST OF THE ISLAND.
SURFACE WINDS AT THE ISLAND HAVE SHIFTED FROM NORTHEAST TO
SOUTH-SOUTHWEST OVER THE PAST COUPLE OF HOURS AS THE ROTATION HAS
BUILT DOWN TOWARDS THE SURFACE AND MOVED TO THE WEST OF THE ISLAND.
A TIMELY 101222Z ASCAT-B BULLSEYE CONFIRMS THAT THE VORTEX TO THE
SOUTH HAS IN FACT BUILT DOWN TO THE SURFACE AND IS STARTING TO
CONNECT TO THE LLCC OF TS 29W, AS THE SCATTEROMETER SHOWS AN
ELONGATED CIRCULATION ORIENTED ALONG A NORTHWEST-SOUTHEAST AXIS.
THE INITIAL POSITION IS PLACED IN THE NORTHWESTERN CORNER OF THIS
ELONGATED ROTATION, CONSISTENT WITH THE RADAR INDICATED LLCC AND
THE TIGHT GROUPING OF AGENCY FIX POSITIONS. THE SCATTEROMETER ALSO
SHOWED 35-40 KNOT WINDS IN THE SOUTHEASTERN QUADRANT, NEAR
MINAMIDAITOJIMA, AND 30-35 KNOT WINDS TO THE WEST AND SOUTHWEST,
PROVIDING CONFIRMATION OF THE INITIAL INTENSITY. ENVIRONMENTAL
CONDITIONS ARE FAVORABLE WITH LOW SHEAR, WARM SSTS AND GOOD DUAL
CHANNEL OUTFLOW ALOFT, COMPLICATED BY THE INTERACTION AND MERGER OF
THE TWO VORTICES WHICH WILL DISRUPT THE INTENSIFICATION PROCESS FOR
A BIT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN, WITH SUBTROPICAL
RIDGING TO THE EAST AND WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 31 KTS AT 101140Z
   CIMSS AIDT: 36 KTS AT 101140Z
   CIMSS D-PRINT: 25 KTS AT 101140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: MERGER WITH LOW- TO MID-LEVEL MESOVORTEX TO THE
SOUTHEAST. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: OVER THE PAST SIX HOURS, TS 29W HAS TURNED
SHARPLY SOUTHWESTWARD, AND OVER THE LAST HOUR APPEARS TO BE MOVING
SOUTHWARD AND MAKING A VERY TIGHT LOOP. THE TRACK SCENARIO TO
HIGHLY COMPLEX, INVOLVING TWO VORTICES DOING THE FUJIWARA DANCE
WITH ONE ANOTHER, EMBEDDED WITHIN A WEAK STEERING ENVIRONMENT. SIX
HOURS AGO, THE MID-LEVEL MESOCYCLONE WAS LOCATED ABOUT 120NM SOUTH
OF TS 29W, BUT NOW THE TWO HAVE STARTED TO MERGE INTO ONE LARGE
CIRCULATION AS DISCUSSED ABOVE. THE HAFS-A MODEL CAPTURED THIS
PROCESS QUITE WELL AND SINCE IT'S DONE SO WELL TO DATE, WE ARE GOING
TO STICK WITH IT. IT DEPICTS A MERGER OF THE TWO VORTICES WITHIN
THE NEXT 12 HOURS, THEN A TRACK NORTHWARD AS THE RIDGE TO THE EAST
STRENGTHENS AND MOVES CLOSER TO TS 29W. IT WILL TAKE ABOUT 24 HOURS
FOR THE VORTEX TO FULLY ALIGN, AND THUS ONLY A SMALL AMOUNT OF
INTENSIFICATION IS EXPECTED THROUGH TAU 24. BUT ONCE THE SYSTEM
COMPLETES AXISYMMETRIZATION, IT WILL BE PRIMED TO TAKE ADVANTAGE OF
A NEAR-OPTIMUM ENVIRONMENT OF VERY WARM SSTS, MODERATELY HIGH OHC,
AND ROBUST POLEWARD OUTFLOW INTO THE BASE OF A STRONG JET MAX OVER
JAPAN. THE SYSTEM ROUNDS THE RIDGE AXIS AROUND TAU 24, AND WILL
THEN ACCELERATE NORTHEASTWARD THROUGH TAU 72, FLATTENING OUT TO A
MORE EASTWARD TRACK BY THE END OF THE FORECAST PERIOD. RAPID
INTENSIFICATION IS POSSIBLE BETWEEN TAU 24 AND TAU 48 AS THIS WILL
BE WHEN THE SYSTEM WILL EXPERIENCE THE MOST FAVORABLE CONDITIONS.
THE PEAK INTENSITY OF 80-85 KNOTS IS NOT CAPTURED DIRECTLY IN THE
FORECAST POINTS BUT IS LIKELY TO OCCUR AROUND TAU 60 AS THE SYSTEM
PASSES SOUTH OF TOKYO. EXTRATROPICAL TRANSITION (ETT) WILL BEGIN BY
TAU 72, WITH COMPLETION OF ETT EXPECTED BY TAU 96. 

MODEL DISCUSSION: WITH THE EXCEPTION OF HAFS-A, WHICH IS NOT A
MEMBER OF THE TRACK CONSENSUS, NO MODEL PICKED UP ON THE ERRATIC
TRACK MOTION SEEN OVER THE PAST FEW HOURS. THE GOOGLE DEEP MIND
(GDM) ENSEMBLE MEAN WAS THE NEXT BEST MODEL, BUT EVEN IT MISSED THE
SOUTHWEST JOG. THE GUIDANCE POINTS ARE IN 12-HR TIME STEPS AND A
LOT OF CRAZINESS CAN HAPPEN IN 12 HOURS. ALL THAT TO SAY THAT THE
SHORT-TERM GUIDANCE IS NOT ACCURATE AND NOT CAPTURING THE LOOPING
MOTION CURRENTLY UNDERWAY. BY TAU 24, THE ENTIRE MODEL PACKAGE
EXCEPT FOR THE ECWMF AND GDM ARE POSITIONED NEAR 30N, WHILE THE
JTWC FORECAST POINT IS A FULL TWO DEGREES OF LATITUDE SOUTH, AN
ATTEMPT TO CAPTURE THE ANTICIPATED COUNTER-CLOCKWISE LOOP AND SLOW
TRACK ACROSS THE RIDGE AXIS. AFTER TAU 24 THE MODELS COME INTO
SLIGHTLY BETTER AGREEMENT, PARTICULARLY IN THE CROSS-TRACK
DIRECTION, WITH THE ENVELOPE MAINTAINING A CONSISTENT 135NM ACROSS
THROUGH TAU 96. ALONG-TRACK UNCERTAINTY IS ANOTHER STORY ALL
TOGETHER, WITH SIGNIFICANT ALONG-TRACK SPREAD IN THE MODEL PACKAGE,
EXCEEDING 500NM AFTER TAU 48. THE JTWC FORECAST IS POSITIONED
SLOWER THAN THE CONSENSUS AT ALL FORECAST TAUS, BUT SLIGHTLY FASTER
THEN THE SLOWEST OF THE MODELS (ECMWF AND NAVGEM). INTENSITY
GUIDANCE HAS NOT CHANGED SIGNIFICANTLY OVER THE PAST SEVERAL RUNS,
WITH THE COAMPS-TC, HAFS-A AND MESOSCALE GFS INDICATING A PEAK
INTENSITY BETWEEN 80-90 KNOTS AND THE SHIPS GUIDANCE SHOWING A MUCH
LOWER PEAK NEAR 50 KNOTS. AS MENTIONED EARLIER, THE COAMPS-TC
ENSEMBLE RI PROBABILITIES CONTINUE TO INCREASE AND ARE NOW UP TO 70
PERCENT BETWEEN TAU 24 AND TAU 48, AND THE CTR1 AND RIDE RI AIDS
ARE TRIPPED WITH THIS RUN, REACHING A PEAK OF 90 KNOTS AS EARLY AS
TAU 48. THE JTWC FORECAST IS PLACED CLOSED TO THE HAFS-A THROUGH
THE ENTIRE FORECAST.  

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