884 

WDPN32 PGTW 170300

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//

SUBJ/PROGNOSTIC REASONING FOR TYPHOON 29W (CHAMPI) WARNING NR 011//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 12.4N 148.6E

   INITIAL INTENSITY: 85 KTS

   GEOGRAPHIC REFERENCE: 230 NM EAST-SOUTHEAST OF ANDERSEN AFB

   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 16 KTS

   SIGNIFICANT WAVE HEIGHT: 34 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)

29W (CHAMPI) WITH A RAGGED, CLOUD-FILLED EYE AND A COMPACT CORE.

29W IS EXHIBITING A WOBBLE IN SHORT-TERM MOTION AS THE EYE

CONTINUES TO DEVELOP, BUT HAS OVERALL MOVED WEST-NORTHWESTWARD OVER

THE PAST SIX HOURS. SOME DRY AIR IS BEGINNING TO ENTRAIN IN FROM

THE EASTERN FLANK AND WRAP AROUND THE NORTHERN SEMICIRCLE, CREATING

A NINE SHAPED CLOUD APPEARANCE WITH FURTHER, SOMEWHAT SEPARATED

CONVECTION MORE EXPANSIVE TO THE SOUTHWEST. DESPITE THE DRY AIR

ENTRAINMENT, ENVIRONMENTAL CONDITIONS ARE ASSESSED TO BE OTHERWISE

FAVORABLE, WITH LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR

(VWS), WARM (28-29 C) SEA SURFACE TEMPERATURES, AND STRONG WESTWARD

AND EQUATORWARD OUTFLOW ALOFT, ALLOWING 29W TO CONTINUE UNDERGOING

RAPID INTENSIFICATION (RI) AS ITS INNER, COMPACT CORE COCOONS

ITSELF. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED

ON RADAR DATA FROM GUAM AS 29W NEARS THE MARIANAS. THE INITIAL

INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION FROM

A 161940Z RCM-2 SAR PASS WITH A VMAX OF 95 KTS. ACCOUNTING FOR SARS

KNOWN HIGH BIAS, THIS SUPPORTS THE INITIAL INTENSITY OF 85 KTS AND IS

ALSO IN GOOD AGREEMENT WITH THE AGENCY DVORAK FIXES AND CIMSS

OBJECTIVE AIDS LISTED BELOW.



INITIAL WIND RADII BASIS: 161940Z RCM-2 SAR DATA



CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE

NORTHEAST



AGENCY DVORAK AND AUTOMATED FIXES:

   PGTW: T5.0 - 90 KTS

   RJTD: T4.5 - 77 KTS

   RCTP: T4.5 - 77 KTS

   CIMSS ADT: 84 KTS AT 162330Z

   CIMSS AIDT: 82 KTS AT 162330Z

   CIMSS D-PRINT: 88 KTS AT 170030Z



FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE

   VWS: 15-20 KTS

   SST: 28-29 CELSIUS

   OUTFLOW: STRONG WESTWARD

   OTHER FACTORS: DRY AIR ENTRAINMENT



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: TY 29W IS FORECAST TO CONTINUE

WEST-NORTHWESTWARD FOR THE NEXT 36 HOURS UNDER THE COMBINED

STEERING INFLUENCE OF THE SUBTROPICAL RIDGE (STR) CENTERED TO THE

NORTHEAST AND THE STR CENTERED OVER TAIWAN. AFTER TAU 36, A

MID-LATITUDE TROUGH IS EXPECTED TO PROPAGATE EASTWARD, CAUSING A

WEAKNESS IN THE RIDGING COMPLEX AND A RESULTANT POLEWARD TURN IN

THE TRACK OF CHAMPI, AS WELL AS SLOWING IN TRACK SPEED. THE STR TO

THE NORTHEAST IS EXPECTED TO THEN REBUILD, CAUSING AN ACCELERATION

AND NORTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD.

REGARDING INTENSITY, 29W IS FORECAST TO CONTINUE RAPIDLY INTENSIFYING

OUT TO TAU 24 AND CONTINUE INTENSIFICATION TO A PEAK OF 135 KTS

BETWEEN TAUS 48 AND 72 AS 29W REMAINS IN A FAVORABLE ENVIRONMENT. VWS

IS EXPECTED TO REMAIN LESS THAN 20 KTS AND OCEAN HEAT CONTENT WILL

INCREASE TO 100-160 KJ PER CM SQUARED BETWEEN TAUS 48 AND 96. THE

CURRENT DRY AIR ENTRAINMENT IS NOT ASSESSED TO BE IMPACTING THE

COMPACT INNER CORE OF THE SYSTEM, AND BY TAU 24 TY 29W IS EXPECTED TO

REGAIN EXTENSIVE MOISTURE CONTENT THROUGHOUT. A PLATEAU IN INTENSITY

AND SLIGHT WEAKENING IS DEPICTED NEAR THE END OF THE FORECAST PERIOD

BUT WITH LESS CERTAINTY DUE TO THE DIFFICULT NATURE OF PREDICTING THE

INTERNAL DYNAMICS OF SUPERTYPHOON STRENGTH SYSTEMS.



MODEL DISCUSSION: TRACK MODEL GUIDANCE CONTINUES TO BE IN GOOD

AGREEMENT IN THE SHORT TERM, WITH A CROSS-TRACK SPREAD OF ONLY 25

NM AT THE POINT OF CPA TO GUAM. HOWEVER, THE WOBBLING MOTION OF THE

SYSTEM IN THE PAST 12 HOURS AND RESULTANT POSITIONS HAVE CAUSED

SEVERAL OF THE TRACKERS TO NOW DEPICT A BRIEF LANDFALL OVER THE

SOUTHERN TIP OF GUAM. WHILE THE OFFICIAL JTWC FORECAST TRACK DOES

NOT DEPICT THIS SCENARIO, IT REMAINS A POSSIBILITY AND CPA TO GUAM

HAS DECREASED AS A RESULT. AFTER TAU 36, CROSS-TRACK SPREAD

INCREASES, RESULTING IN 170 NM AND AN ALONG-TRACK SPREAD OF 180 NM

AT TAU 120, DUE TO A DIFFERENCE IN THE TIMING OF THE POLEWARD TURN.

HOWEVER, ALL MODELS ARE IN GOOD AGREEMENT IN DEPICTING THE DIRECT

NORTHWESTWARD TRACK. THE OFFICIAL JTWC FORECAST TRACK IS THUS LAID

WITH HIGH CONFIDENCE OUT TO TAU 72 AND MEDIUM CONFIDENCE

THEREAFTER, CLOSELY IN LINE WITH THE MULTI-MODEL AND AI CONSENSUS.

REGARDING INTENSITY, GFS AND GFS-BASED INTENSITY MODELS (COAMPS-TC,

DECAY SHIPS) CONTINUE TO BE OUTLIERS ON THE LOW END, INITIALIZING

THE SYSTEM AT A LOWER INTENSITY AND DEPICTING A MUCH MORE GRADUAL

INTENSIFICATION. ON THE OTHER END, SEVERAL RI AIDS CONTINUE TO

POPULATE, AND THE UPPER-END PEAKS PREDICTED BY HAFS-A AND THE

OPERATIONAL AND EXPERIMENTAL GOOGLE DEEPMIND MODELS HAVE REMAINED

CONSISTENT WITH PREVIOUS CYCLES, RANGING FROM 135-150 KTS. THE

OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE

FOR THE ENTIRETY OF THE FORECAST PERIOD, IN LINE WITH THE

OPERATIONAL GOOGLE DEEPMIND BUT JUST BELOW ITS PEAK INTENSITY.



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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