Advisories

WDPN32 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 29W (CHAMPI) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.5N 156.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 692 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 29W FORMING A NASCENT CENTRAL DENSE OVERCAST THAT IS
OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) BELOW. THE BULK
OF DEEP CONVECTION REMAINS WEST OF THE SYSTEM, IMPACTED BY THE
EASTERLY VERTICAL WIND SHEAR (VWS). A THIN LINE OF CIRRUS OUTFLOW
APPEARS TO BE ATTEMPTING UPSHEAR EXPANSION, A SIGN THE SYSTEM COULD
BE BEGINNING TO RESIST THE PRESSURE AND CONSOLIDATE. THE 151746Z
SSMIS MICROWAVE DATA REVEALS A COMPACT SURFACE CIRCULATION WITH THE
SMALL PATCH OF CENTRAL CONVECTION DISPLACED TO THE WEST, CONFIRMING
THE SLIGHT WESTWARD VERTICAL TILT. ENVIRONMENTAL ANALYSIS REVEALS A
FAVORABLE ENVIRONMENT, CHARACTERIZED BY LOW (10-15 KTS) VERTICAL
WIND SHEAR (VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES (SST),
DECENT (75-100 KJ PER CM SQUARED) OCEAN HEAT CONTENT (OHC) AND
MODERATE OUTFLOW SUPPORTED BY THE EASTERLY FLOW. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED
SSMIS DATA. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND THE AUTOMATED CIMSS
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE SOUTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 40 KTS AT 151740Z
   CIMSS ADT: 49 KTS AT 151740Z
   CIMSS AIDT: 39 KTS AT 151740Z
   CIMSS D-MINT: 33 KTS AT 151722Z
   CIMSS D-PRINT: 43 KTS AT 151810Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 29W (CHAMPI) IS FORECAST TO CONTINUE
STEADILY TRACKING WEST-NORTHWESTWARD THROUGH TAU 36 WHILE IT
REMAINS ON THE SOUTHERN PERIPHERY OF THE STEERING STR CENTERED FAR TO 
THE NORTH. AT 
ABOUT TAU 36, A DEEP-LAYER TROUGH IS EXPECTED TO PASS TO THE NORTH,
WEAKENING THE RIDGE AND FORCING IT TO RETREAT EASTWARD.
SIMULTANEOUSLY, A SECOND STR IS EXPECTED TO BUILD IMMEDIATELY
FOLLOWING THE PASSAGE OF THE TROUGH AND ASSUMING STEERING INFLUENCE
OVER 29W FROM TAU 36-120. IT IS EXPECTED TO BE A SMOOTH TRANSITION
FROM ONE STR TO THE OTHER, AND THE NEW STEERING ENVIRONMENT WILL
MAINTAIN THE STEADY WEST-NORTHWESTWARD TRACK FOR THE REMAINDER OF
THE FORECAST PERIOD. REGARDING INTENSITY, 29W IS FORECAST TO
STEADILY INTENSIFY THROUGH TAU 12 WHILE THE SYSTEM CONTINUES TO
CONSOLIDATE AND ORGANIZE. FOLLOWING TAU 24, 29W IS FORECAST TO
UNDERGO A PROLONGED PERIOD OF RAPID INTENSIFICATION (RI) IN
RESPONSE TO THE INCREASINGLY FAVORABLE ENVIRONMENT IT WILL
ENCOUNTER BETWEEN TAU 24-72. THOUGH VWS IS EXPECTED TO REMAIN
APPROXIMATELY 15KTS THROUGH TAU 96, THE EQUATORWARD AND
WESTWARD OUTFLOW CHANNELS ARE EXPECTED TO STRENGTHEN AND CHAMPI IS
EXPECTED TO TRACK THROUGH A REGION OF SLIGHTLY HIGHER (100-125 KJ
PER CM SQUARED) OHC. AFTER TAU 72, 29W WILL CONTINUE TO INTENSIFY
GRADUALLY UNTIL PEAKING AT TAU 96. AFTER THAT POINT, 29W WILL
LIKELY MAINTAIN A HIGH INTENSITY, AS ENVIRONMENTAL CONDITIONS WILL
CONTINUE TO IMPROVE. NAMELY, VWS IS EXPECTED TO DROP TO LESS THAN
10KTS BY TAU 96 AND OHC IS EXPECTED TO INCREASE TO ABOVE 150 KJ PER
CM SQUARED. THIS ENVIRONMENT SHOULD HAVE NO ISSUE SUSTAINING A
STRONG TYPHOON, HOWEVER, THE POTENTIAL FOR AN EYEWALL REPLACEMENT
CYCLE (ERC) INCREASES, WHICH WOULD CAUSE A MOMENTARY DROP IN
INTENSITY. AS A RESULT, THE INTENSITY BETWEEN TAU 96-120 REMAINS
RELATIVE STABLE. THE POTENTIAL OF A PEAK INTENSITY GREATER THAN 130
KTS IS ALSO WITHIN THE REALM OF POSSIBILITY, DEPENDING ON HOW
QUICKLY 29W IS ABLE TO CONSOLIDATE BETWEEN TAU 0-24, THEREBY
IMPACTING WHEN THE SYSTEM IS ABLE TO COMMENCE RAPIDLY INTENSIFYING.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGHOUT THE FORECAST PERIOD, BUT PARTICULARLY THROUGH
THE FIRST 48 HOURS. THE CROSS-TRACK SPREAD AS THE STORM PASSES
THROUGH THE NORTHERN MARIANAS IS 85 NM, EVEN INCLUDING TWO OUTLIERS
(GFS AND GEFS). DISCOUNTING THOSE, THE CROSS-TRACK SPREAD DROPS TO
55 NM AT CPA, WITH THE BULK OF GUIDANCE SUPPORTING A TRACK THAT
CLIPS THE NORTHERN COAST OF GUAM OR PASSES JUST OFFSHORE. THE
EXCELLENT MODEL AGREEMENT FOR THE FIRST 72 HOURS SUPPORTS THE JTWC
NEAR-TERM TRACK FORECAST WITH HIGH CONFIDENCE. AFTER TAU 72, THE
GUIDANCE SPREADS A MINIMAL AMOUNT, COMPOUNDING TO A 200 NM
CROSS-TRACK SPREAD AT TAU 120 (EXCLUDING GFS AND GEFS), LENDING
HIGH CONFIDENCE TO THE LATE-TERM JTWC TRACK FORECAST. THE JTWC
TRACK FORECAST IS PLACED IN CLOSE AGREEMENT WITH THE MULTI-MODEL
CONSENSUS, EXPERIMENTAL AI CONSENSUS, AND GOOGLE DEEPMIND WITH
OVERALL HIGH CONFIDENCE. RELIABLE INTENSITY AIDS ARE IN GOOD
AGREEMENT THROUGH TAU 36, THOUGH THERE IS SOME DISAGREEMENT
REGARDING THE TIMING OF RI. SEVERAL JTWC RI INDICATORS HAVE REACHED
TRIP CRITERIA, SUPPORTING THE POSSIBILITY OF RI OCCURRING WITHIN THE
NEXT 24-48 HOURS. HOWEVER, THE HAFS-A AND HWRF SOLUTIONS DEPICT RI
BEGINNING AS LATE AS TAU 60. MODEL GUIDANCE ALSO DISAGREES ON THE
PEAK INTENSITY AND THE TIMING OF THE PEAK. THE PEAK INTENSITY
SPREAD RANGES FROM 105 KTS AND 135 KTS, WITH THE TIMING SPREAD
BETWEEN TAU 72 AND TAU 120. THE JTWC INTENSITY FORECAST IS IN CLOSE
AGREEMENT WITH THE RI AIDS AND THE BULK OF MODELS FROM TAU 0-24,
THEN HEDGED CLOSE TO THE MESOSCALE MODELS AND GOOGLE DEEPMIND FROM
TAU 24 THROUGH THE END OF THE FORECAST PERIOD. THE JTWC INTENSITY
FORECAST IS ASSESSED WITH OVERALL MEDIUM CONFIDENCE.

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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