Advisories

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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