Advisories

WDPN32 PGTW 151500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.0N 157.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 750 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
EXPLOSIVE DEEP CONVECTION PERSISTING ALONG THE WESTERN SIDE OF THE
CIRCULATION WITH EXPANDING UPPER-LEVEL OUTFLOW. THE OVERSHOOTING
CLOUD TOPS HAVE REACHED TEMPERATURES AS COLD AS -97 DEGREES
CELSIUS. THE SYSTEM IS LIKELY STILL TILTED SOUTHWESTWARD WITH
HEIGHT AND BATTLING MODERATE NORTHEASTERLY VERTICAL WIND SHEAR
(VWS). HOWEVER, THE SYSTEM MAY BE BRIEFLY OVERCOMING THE EFFECTS OF
VWS AS GRAVITY WAVES EMANATE RADIALLY FROM THE DEEP CONVECTION.
MOST NOTABLY, THE LOW-LEVEL CIRCULATION CENTER (LLCC) HAS BECOME
EMBEDDED IN THE NASCENT CENTRAL DENSE OVERCAST (CDO), WITH CURVED
BANDING BEGINNING TO DEVELOP ALONG THE NORTHERN PERIPHERY. A
151025Z ASCAT-C PASS REVEALED AN ELONGATED LLCC WITH GALE-FORCE
WINDS CONFINED TO THE SOUTHERN SEMICIRCLE. BASED ON THESE DATA AND
THE IMPROVED CONVECTIVE STRUCTURE, 29W HAS BEEN UPGRADED TO A 35-KT
TROPICAL STORM (TS) WITH HIGH CONFIDENCE. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE, EXTRAPOLATED FROM THE SCATTEROMETER
DATA AND HEDGED TOWARD THE NORTHEAST SIDE OF THE RAGGED CDO. THE
ENVIRONMENT IS GENERALLY FAVORABLE FOR ADDITIONAL INTENSIFICATION,
CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30
DEGREES CELSIUS, MODERATE UPPER-LEVEL DIVERGENCE FOCUSED ALONG THE
WESTERN PERIPHERY, AND PLENTIFUL DEEP-LAYER MOISTURE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A LOW- TO MID-LEVEL
SUBTROPICAL RIDGE (STR) CENTERED NEAR 30N 160E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   CIMSS ADT: 41 KTS AT 151140Z
   CIMSS AIDT: 35 KTS AT 151140Z
   CIMSS D-MINT: 38 KTS AT 151148Z
   CIMSS D-PRINT: 40 KTS AT 151240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INTENSITY FORECAST HAS BEEN
ADJUSTED UPWARD BY 5-10 KTS FROM TAU 12 TO TAU 72.

FORECAST DISCUSSION: TS 29W IS MOVING WEST TO WEST-NORTHWESTWARD
ALONG THE SOUTHERN PERIPHERY OF THE STR. THIS RIDGE WILL ERODE FROM
TAU 24 TO TAU 48 AS A TROUGH PASSES WELL TO THE NORTH. MEANWHILE, A
SHARP MID-LEVEL TROUGH APPROACHING THE KOREAN PENINSULA WILL
SUPPORT THE DEVELOPMENT OF A NEW STR OVER HONSHU. THIS RIDGE WILL
SETTLE EAST OF HONSHU NEAR TAU 72 AND BECOME THE PRIMARY STEERING
MECHANISM FOR TS 29W, MAINTAINING A WEST-NORTHWESTWARD TRAJECTORY
THROUGH TAU 120. THE RECENT EXPLOSIVE CONVECTION AND ONGOING VORTEX
CONSOLIDATION MAY FORESHADOW SIGNIFICANT INTENSIFICATION ONCE
AXISYMMETRIZATION IS ACHIEVED. VWS WILL EASE TOWARD TAU 60, WHILE
TS 29W TRAVERSES VERY WARM SST OF 29-30 DEGREES CELSIUS. THE
FORECAST CALLS FOR THE SYSTEM TO BECOME SUFFICIENTLY ORGANIZED TO
BEGIN RAPID INTENSIFICATION (RI) NEAR TAU 36, REACHING TYPHOON
STRENGTH SHORTLY THEREAFTER AND PEAKING AT 125 KTS AT TAU 96.
ALTHOUGH THE ENVIRONMENT BECOMES EVEN MORE FAVORABLE AFTER TAU 72,
CHARACTERIZED BY WARMER SST, HIGHER OHC, AND 5-10 KTS OF VWS, THE
FORECAST CONSERVATIVELY LEVELS OFF THE INTENSITY AFTER TAU 96 TO
ACCOUNT FOR DIFFICULT-TO-PREDICT FLUCTUATIONS IN INTENSITY CAUSED
BY INTERNAL TROPICAL CYCLONE DYNAMICS.

MODEL DISCUSSION: THE OVERALL TRACK GUIDANCE REMAINS TIGHT BUT HAS
SHIFTED SOUTHWARD ONCE AGAIN. THE BULK OF THE DYNAMICAL AIDS LIES
ON THE POLEWARD SIDE OF THE GUIDANCE ENVELOPE, WHILE THE AI MODELS
LEAN TOWARD A MORE WESTWARD TRAJECTORY. GOOGLE DEEPMIND HAS ALSO
SHIFTED SOUTHWARD AND NOW TAKES THE SYSTEM 30 NM SOUTH OF GUAM. THE
MULTI-MODEL CONSENSUS (CONW) AND ECMWF ARE AIMED AT CENTRAL TO
NORTHERN GUAM, WHILE GFS AND NAVGEM TARGET THE CHANNEL BETWEEN ROTA
AND GUAM. THE AI-MODEL MEAN CLIPS THE SOUTHERN TIP OF GUAM. NEARLY
ALL MODELS TRACK THE SYSTEM SOUTH OF ROTA, WITH THE CROSS-TRACK
SPREAD AMONG THE RELIABLE AIDS NEAR THE CPA TO GUAM MEASURING 70
NM. THE JTWC FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS
FORECAST, POSITIONED BETWEEN CONW AND THE AI-MODEL MEAN BUT HEDGED
CLOSER TO THE AI-MODEL MEAN. IF CURRENT TRENDS CONTINUE, SUBSEQUENT
FORECASTS MAY NEED TO SHIFT THE TRACK FARTHER SOUTH. THE INTENSITY
AIDS HAVE TRENDED STRONGER THIS CYCLE. DEEPMIND NOW DEPICTS VERY
AGGRESSIVE INTENSIFICATION, BRINGING TS 29W TO 115-130 KTS BY TAU
60. HAFS-A AND GFS ARE SLOWER TO INTENSIFY THE SYSTEM FOR THE FIRST
60 HOURS. HOWEVER, HAFS-A EVENTUALLY STRENGTHENS TS 29W TO 155 KTS
AT THE END OF THE FORECAST PERIOD. THE COAMPS-TC AND DEEPMIND
ENSEMBLES PEG THE RI PROBABILITY NEAR 80 PERCENT, WITH 75-85
PERCENT OF THE MEMBERS ACHIEVING SUPER TYPHOON INTENSITY BY TAU 96.
THE JTWC INTENSITY FORECAST HAS BEEN INCREASED BY 5-10 KTS FROM TAU
12 THROUGH TAU 72, WHILE THE TAU 96 AND TAU 120 FORECAST
INTENSITIES REMAIN UNCHANGED. THE FORECAST LIES NEAR THE CENTER OF
THE GUIDANCE ENVELOPE THROUGH TAU 48, THEN TRENDS TOWARD THE UPPER
END OF THE ENVELOPE BY TAU 96 AND TAU 120. IF TS 29W CONTINUES TO
CONSOLIDATE AT THE CURRENT RATE, SUBSEQUENT INTENSITY FORECASTS MAY
NEED TO BE FURTHER INCREASED.

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