Advisories

WDPN32 PGTW 160900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.4N 152.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 477 NM EAST-SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 29W HAS STEADILY BECOME BETTER ORGANIZED. DEEP
CONVECTION HAS NOW WRAPPED AROUND THE EASTERN SIDE OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC), AND SPIRAL BANDS EXTEND OUTWARD ALONG
THE NORTHERN PERIPHERY. UPPER-LEVEL OUTFLOW HAS BECOME MORE RADIAL
AS THE MODERATE NORTHEASTERLY SHEAR THAT HAD BEEN PLAGUING THE
SYSTEM EASES. AN EARLIER 152259Z ASCAT-C PASS REVEALED ASYMMETRIES
IN THE WIND FIELD, THOUGH THE RECENT INCREASE IN CURVED CONVECTION
SUGGESTS THAT THESE ASYMMETRIES MAY BE DIMINISHING. FURTHERMORE,
THE PREVIOUSLY PARTIALLY EXPOSED LLCC NOW APPEARS FULLY EMBEDDED
BENEATH THE CENTRAL CONVECTION, INDICATING INCREASING VORTEX
ALIGNMENT. MORE CRITICALLY, A VITAL 160611Z GMI PASS DEPICTED A
CLOSED INNER CORE REPRESENTED BY THE DREADED CYAN RING SURROUNDING
A 15-NM WIDE MICROWAVE EYE FEATURE. THE ENVIRONMENT IS FAVORABLE,
CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) AND LOW
TO MODERATE VERTICAL WIND SHEAR (VWS). SUBJECTIVE DVORAK ESTIMATES
HAVE COME IN AT T3.5. BASED ON THE RISING SUBJECTIVE AND OBJECTIVE
ESTIMATES, THE INITIAL INTENSITY HAS BEEN RAISED TO 50 KTS, WHICH
COULD BE CONSERVATIVE. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE TIGHTLY CURVED BANDING.

INITIAL WIND RADII BASIS: EXTRAPOLATION OF SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE CENTERED NEAR 28N 157E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 47 KTS AT 160410Z
   CIMSS ADT: 55 KTS AT 160540Z
   CIMSS AIDT: 46 KTS AT 160540Z
   CIMSS D-MINT: 44 KTS AT 160306Z
   CIMSS D-PRINT: 46 KTS AT 160540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE OVERALL FORECAST TRACK HAS
SHIFTED SOUTHWARD, AND THE FORECAST INTENSITY HAS BEEN INCREASED BY
10 KTS FROM TAU 12 TO TAU 60.

FORECAST DISCUSSION: TS 29W IS MOVING NEARLY DUE WEST ALONG THE
SOUTHERN PERIPHERY OF A STR. OVER THE NEXT 24 HOURS, A TROUGH
PASSING FAR TO THE NORTH WILL ERODE THE RIDGE. THE WEAKENING RIDGE
WILL ALLOW FOR A WEST-NORTHWESTWARD MOTION. MEANWHILE, A SEPARATE
TROUGH WILL APPROACH THE KOREAN PENINSULA BY TAU 36 AND SUPPORT THE
DEVELOPMENT OF A RIDGE OVER HONSHU, MAINTAINING THE
WEST-NORTHWESTWARD TRACK THROUGH TAU 72. THIS RIDGE WILL SETTLE
SOUTHEAST OF JAPAN BY TAU 72 AND INDUCE A NORTHWESTWARD TRAJECTORY
FOR THE LATTER PART OF THE FORECAST PERIOD. THE CYAN RING OBSERVED
IN THE GMI 37 GHZ IMAGE SUPPORTS RAPID INNER-CORE CONSOLIDATION
WHEN THE ENVIRONMENT IS FAVORABLE. WITH THE ENVIRONMENT REMAINING
LARGELY CONDUCIVE, CHARACTERIZED BY 10-15 KTS OF VWS, SST OF 29-30
DEGREES CELSIUS, AND OHC NEAR 100 KJ PER CM2, TS 29W HAS VERY
LIKELY BEGUN A PERIOD OF RAPID INTENSIFICATION (RI). IN FACT, THE
ENVIRONMENT WILL BECOME EVEN MORE FAVORABLE AFTER TAU 48, WITH VWS
EASING TO 5-10 KTS. THE FORECAST NOW CALLS FOR A PROLONGED EPISODE
OF RI THROUGH TAU 60, AFTER WHICH DIFFICULT-TO-PREDICT FLUCTUATIONS
IN INTENSITY MAY OCCUR DUE TO INTERNAL TROPICAL CYCLONE DYNAMICS.
HAFS-A HAS CONSISTENTLY INDICATED THE POTENTIAL FOR AN EYEWALL
REPLACEMENT CYCLE (ERC) TO BEGIN 24-36 HOURS AFTER THE SYSTEM
PASSES THE SOUTHERN MARIANA ISLANDS. THE WIND FIELD OF TS 29W WILL
GRADUALLY EXPAND, BECOMING LARGE BY THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE
FORECAST PERIOD. EXCLUDING THE SLIGHTLY POLEWARD OUTLIERS OF JGSM
AND HAFS-A, THE CROSS-TRACK SPREAD IS 35 NM NEAR THE CPA TO GUAM
AND APPROXIMATELY 250 NM AT TAU 120. THE OVERALL GUIDANCE SUITE HAS
SHIFTED SOUTHWARD THIS CYCLE, AND THE BULK OF THE GUIDANCE,
CONSISTING OF AN INTERMIXED CORE OF BOTH DYNAMICAL AND AI MODELS,
NOW DEPICTS A PASSAGE SOUTH OF GUAM. HAFS-A AND JGSM ARE THE ONLY
SOLUTIONS THAT BRING THE SYSTEM BETWEEN ROTA AND GUAM. THE JTWC
FORECAST TRACK HAS THEREFORE SHIFTED SOUTHWARD, THOUGH IT REMAINS
POLEWARD OF THE CORE GROUP OF MODELS. IF TRENDS CONTINUE,
ADDITIONAL SOUTHWARD ADJUSTMENTS IN THE TRACK MAY BE REQUIRED.
SEVERAL RI AIDS HAVE TRIGGERED, AND THE DEEPMIND ENSEMBLE GIVES A
90 PERCENT CHANCE OF RI, WITH NEARLY 70 PERCENT OF ITS MEMBERS
ATTAINING SUPER TYPHOON STRENGTH BY TAU 60. THE JTWC INTENSITY
FORECAST HAS BEEN INCREASED BY 10 KTS THROUGH TAU 60, LYING AT THE
UPPER END OF THE GUIDANCE ENVELOPE AND IS NEARLY ALIGNED WITH
DEEPMIND. GIVEN RECENT TRENDS ON SATELLITE IMAGERY, EVEN THIS
FORECAST MAY PROVE CONSERVATIVE. THERE IS STILL ROOM FOR FUTURE
UPWARD ADJUSTMENTS IN INTENSITY PRIOR TO THE CPA TO GUAM. THE
STRONGEST INTENSITY AIDS DEPICT UP TO 110 KTS AT TAU 36 AND 120 KTS
AT TAU 48. BOTH THE DEEPMIND AND HAFS-A SOLUTIONS DEPICT A PEAK OF
135-140 KTS AT TAU 72.

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