WDPN31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (NAKRI) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.1N 134.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 406 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED BUT WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC), WITH
AN AREA OF PERSISTENT DEEP CONVECTION LOCATED TO THE SOUTHWEST OF
THE LLCC. A 090538Z GMI 37GHZ MICROWAVE IMAGE REVEALED SHALLOW
BANDING FEATURES WRAPPING INTO A WELL-DEFINED CENTER, AND THE
POCKET OF DEEP CONVECTION TO THE SOUTH-SOUTHWEST OF THE LLCC. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
EXPOSED LLCC. THE INITIAL INTENSITY IS SET TO 35 KNOTS, CONSISTENT
WITH THE REANALYZED PREVIOUS INTENSITY ESTIMATES, BASED ON A BLEND
OF AVAILABLE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED
BELOW. TROPICAL STORM (TS) 29W CONTINUES TO STRUGGLE TO DEVELOP,
HINDERED BY PERSISTENT, MODERATE EAST-NORTHEAST SHEAR. HOWEVER,
OVER THE PAST SIX HOURS, THE SHEAR HAS DROPPED OFF CONSIDERABLY, AS
TY 28W CONTINUES TO ACCELERATE TO THE NORTHEAST, OPENING UP THE
DISTANCE BETWEEN THE TWO SYSTEMS. THE UPPER-LEVEL PATTERN IS ALSO
CHANGING, WITH A COL REGION NOW POSITIONED JUST NORTH OF TS 29W AND
A 200MB ANTICYCLONE DEVELOPING IVO MINAMIDAITOJIMA, ALLOWING FOR
THE REDUCTION IN SHEAR SEEN OVER THE PAST SIX HOURS OR SO. HOWEVER,
WHILE THE LATEST SOUNDING FROM MINAMIDAITOJIMA SHOWS LIGHT WINDS
THROUGH THE COLUMN, IT ALSO SHOWS VERY DRY AIR ABOVE ABOUT 800MB.
WHILE SSTS REMAIN WARM, THE CONGLOMERATION OF DRY AIR, WEAK OUTFLOW
ALOFT AND PERSISTENT, IF WEAKENING, EASTERLY SHEAR ARE CONSPIRING
TO HOLD TS 29W BACK FOR THE MOMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 090640Z
   CIMSS ADT: 35 KTS AT 090530Z
   CIMSS AIDT: 36 KTS AT 090530Z
   CIMSS D-MINT: 28 KTS AT 090538Z
   CIMSS D-PRINT: 29 KTS AT 090640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK WESTWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ALONG THE NORTHWESTERN
PERIPHERY OF THE ROTATION. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE STEERING ENVIRONMENTAL FOR TROPICAL STORM
(TS) 29W REMAINS COMPLEX, WITH A DEEP-LAYER SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST, A COL REGION OR WEAKNESS TO THE NORTH
AND ANOTHER STR CENTERED OVER COASTAL CHINA SOUTH OF SHANGHAI. THE
TWO MAIN INFLUENCES ON THE TRACK FORECAST FOR THE MOMENT ARE THE
RIDGE TO THE EAST AND THE COL REGION TO THE NORTH. TS 29W IS
FORECAST TO CONTINUE TRACKING NORTHWESTWARD OVER THE NEXT 36 HOURS,
ALONG THE LOW-TO-MID-LEVELS OF THE SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST AND TOWARDS THE WEAKNESS IN THE RIDGE
DEFINED BY THE COL REGION. NO SIGNIFICANT CHANGES ARE EXPECTED IN
THE STEERING PATTERN THROUGH TAU 36 OTHER THAN THE FACT THAT THE
STR TO THE EAST WILL SLIDE WESTWARD, CLOSING THE DISTANCE BETWEEN
IT AND TS 29W, THUS TIGHTENING THE STEERING GRADIENT, WHILE
SIMULTANEOUSLY THE RIDGE OVER CHINA WILL MAINTAIN POSITION WHILE
WEAKENING. AFTER TAU 36, TS 29W WILL MOVE INTO THE COL REGION
BETWEEN THE TWO COMPETING RIDGES, THUS SLOWING SIGNIFICANTLY AS IT
DRIFTS NORTHWARD TO THE EAST OF AMAMIOSHIMA. A PERIOD OF NEAR
QUASI-STATIONARY CANNOT BE RULED OUT BETWEEN TAU 36 AND TAU 48 AS
THE SYSTEM WILL BE AT THE RIDGE AXIS DURING THIS TIME. AFTER TAU
48, TS 29W IS FORECAST TO RAPIDLY ACCELERATE NORTHEASTWARD AS IT
ROUNDS THE RIDGE AXIS AND COMES UNDER THE STEERING INFLUENCE OF THE
STRONG STR WHICH AT THIS POINT WILL BE POSITIONED TO THE SOUTHEAST.
THE RIDGE WILL QUICKLY SLIDE WESTWARD, AND TS 29W WILL ACCELERATE
NORTHEASTWARD ALONG THE TOP OF THE RIDGE THROUGH THE REMAINDER OF
THE FORECAST PERIOD. IN TERMS OF INTENSITY, DUE TO THE MARGINAL
CONDITIONS (WEAK OUTFLOW, DRY MID-LEVEL AIR, AND PERSISTENT SHEAR),
THE SYSTEM IS NOT FORECAST TO INTENSIFY THROUGH TAU 36. IN FACT, IT
REMAINS POSSIBLE IT COULD BRIEFLY WEAKEN BELOW TROPICAL STORM
STRENGTH IN THE NEXT 24 HOURS. AS IT APPROACHES THE RIDGE AXIS,
SHEAR WILL BE AT A MINIMUM AND OUTFLOW WILL BEGIN TO IMPROVE, THUS
ALLOWING FOR SOME INTENSIFICATION. AFTER THE SYSTEM ROUNDS THE
RIDGE AXIS, UPPER-LEVEL CONDITIONS, ESPECIALLY THE ONSET OF ROBUST
POLEWARD OUTFLOW, ALLOWING A MORE RAPID PACE OF INTENSIFICATION
THROUGH TAU 96 AS THE SYSTEM MOVES ALONG THE KUROSHIO CURRENT.
AFTER REACHING PEAK INTENSITY, THE SYSTEM WILL BEGIN TO WEAKEN BY
THE END OF THE FORECAST PERIOD, AS IT BEGINS TO BE SHEARED APART,
MOVES OVER COOLER WATERS AND BEGINS EXTRATROPICAL TRANSITION (ETT).

MODEL DISCUSSION: DETERMINISTIC TRACK MODELS ALL AGREE ON THE
OVERALL TRACK SCENARIO, WITH THE MAIN DIFFERENCE SHOWING UP IN THE
ALONG-TRACK AXIS. THE GEFS MEAN MARKS THE EASTERN OR INSIDE EDGE OF
THE TRACK ENVELOPE, WHILE THE NAVGEM AND JGSM MARK THE WESTERN OR
OUTSIDE EDGE. BY TAU 36, CROSS-TRACK SPREAD INCREASES TO 75NM,
MAINTAINING THAT VALUE THROUGH TAU 72, THOUGH BY THAT POINT THE
ECMWF AND GFS WILL MARK THE INSIDE EDGE OF THE GUIDANCE PACKAGE.
SIGNIFICANT ALONG-TRACK SPREAD SHOWS UP AS EARLY AS TAU 48, AS THE
ECMWF IS MUCH SLOWER TO PUSH THE SYSTEM THROUGH THE COL, WHILE THE
GFS AND GEFS IN PARTICULAR, IS MUCH FASTER. BEYOND TAU 72, CROSS-
AND ALONG-TRACK SPREAD INCREASE SHARPLY, WITH CROSS-TRACK SPREAD
INCREASING TO 200NM BY TAU 120, WHILE ALONG-TRACK SPREAD IS UP TO
615NM BETWEEN THE SLOW NAVGEM AND FAST GFS AT TAU 120. ENSEMBLES
INCLUDING GEFS, ECENS, EC-AIFS AND GOOGLE DEEP MIND ARE CONSISTENT
WITH ONE ANOTHER FOR THE MOST PART. AIFS SHOWS THE MOST SPREAD,
FOLLOWED BY ECENS, BOTH OF WHICH SHOW A SIGNIFICANT NUMBER OF
MEMBERS OVER OR WEST OF OKINAWA. THE OTHER ENSEMBLES DEPICT A
TIGHTER TRACK ENVELOPE WHICH REMAINS WELL TO THE EAST AND NORTH OF
OKINAWA. THE JTWC FORECAST IS PLACED NEAR THE ECMWF AND GFS
DETERMINISTIC TRACKERS THROUGH TAU 48, THEN CLOSE TO THE CONSENSUS
MEAN THEREAFTER. CONFIDENCE IS MEDIUM IN THE NEAR TERM, AND LOW IN
THE LATER TAUS DUE TO THE UNCERTAINTY SURROUNDING THE TRACK
SLOWDOWN AS THE SYSTEM NEARS THE RIDGE AXIS. INTENSITY GUIDANCE IS
MIXED. THE SHIPS GUIDANCE PEAKS THE SYSTEM SHORT OF 60 KNOTS, WHILE
THE CTCX, HAFS-A, COTC AND THE GFS MESOSCALE ALL FORM A TIGHT GROUP
SHOWING A PEAK INTENSITY AT TAU 96 BETWEEN 80-90 KNOTS, WITH THE
RAMP UP BEGINNING AROUND TAU 36. THE JTWC FORECAST IS PLACED BELOW
THE CONSENSUS MEAN THROUGH TAU 48, THEN FOLLOWS THE HAFS-A THROUGH
THE REMAINDER OF THE FORECAST, WITH MEDIUM CONFIDENCE. 

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