Advisories

WDPN31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.7N 153.5E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 681 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 54 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MATURE,
DONUT-SHAPED TYPHOON FEATURING A LARGE, 30 NM WIDE EYE EMBEDDED
WITHIN A CENTRAL DENSE OVERCAST THAT EXHIBITS A SMOOTH CANOPY,
INDICATIVE OF EXPANDED AND ROBUST RADIAL OUTFLOW ALOFT. ON INFRARED
IMAGERY ENHANCED BY THE BD CURVE, THE CDO IS DEFINED BY A SOLID
RING OF COLD CLOUD TOPS INDICATED BY BLACK AND WHITE SHADES
ATTEMPTING TO FULLY ENCIRCLE THE EYE, WITH A PERSISTENT CONVECTIVE
BAND ALONG THE WESTERN PERIPHERY. THE SYSTEM APPEARS TO BE
PREPARING FOR A FOURTH EYEWALL REPLACEMENT CYCLE (ERC). THE 011923Z
SSMIS PASS INDICATES THAT AN INTENSE OUTER BAND HAS WRAPPED NEARLY
70 PERCENT AROUND THE PRIMARY EYEWALL. FURTHER INSIGHT WAS PROVIDED
BY A 012324Z ASCAT-B PASS, WHICH REVEALED AN ASYMMETRIC WIND FIELD
WITH LARGER WIND RADII IN THE NORTHERN SEMICIRCLE. THIS ASYMMETRY
IS LIKELY THE RESULT OF MODEST BUT PERSISTENT SOUTHERLY MID-LEVEL
VERTICAL WIND SHEAR (VWS). THE SURROUNDING ENVIRONMENT IS GENERALLY
FAVORABLE, CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURE,
MODERATE OCEAN HEAT CONTENT (OHC), AND GOOD DIVERGENCE ALOFT OFFSET
BY THE AFOREMENTIONED LOW TO MODERATE SHEAR. THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE CIRCULAR, CLOUD-FREE
EYE. AS THE CONVECTIVE STRUCTURE HAS NOT CHANGED SIGNIFICANTLY IN
THE PAST 6 HOURS, THE INITIAL INTENSITY HAS BEEN HELD AT 125 KTS
WITH MEDIUM CONFIDENCE, WHICH IS SUPPORTED BY THE T6.5 FROM PGTW
AND RCTP AND THE HIGHER END OF THE OBJECTIVE ESTIMATES FROM CIMSS
RANGING FROM 116 KTS TO 126 KTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN EXTENSION OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.5 - 127 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 126 KTS AT 012130Z
   CIMSS ADT: 117 KTS AT 020000Z
   CIMSS AIDT: 116 KTS AT 020000Z
   CIMSS D-MINT: 119 KTS AT 011940Z
   CIMSS D-PRINT: 120 KTS AT 020000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 12W WILL MAINTAIN ITS WEST-NORTHWESTWARD
TRAJECTORY AT 13-14 KTS, STEERED ALONG THE SOUTHWESTERN PERIPHERY
OF A STR CENTERED NEAR 43N 177W. THE WESTERN EXTENSION OF THIS
RIDGE WILL CONTINUE TO BUILD, DRIVING THE SYSTEM IN THE SAME
GENERAL DIRECTION. BY TAU 48, A SEPARATE RIDGE OVER THE KOREAN
PENINSULA WILL BECOME THE DOMINANT STEERING MECHANISM, MAINTAINING
THE WEST-NORTHWESTWARD MOTION AND GUIDING THE SYSTEM TOWARD A VERY
CLOSE PASSAGE TO IWO TO. IN THE EXTENDED FORECAST, THE STORM'S
FORWARD MOTION WILL DECREASE TO 10 KTS BY TAU 96. THE DECELERATION
WILL BE CAUSED BY A LARGE CYCLONE OVER EASTERN SIBERIA, WHICH WILL
ERODE THE RIDGE AND LEAD TO A WEAKER STEERING GRADIENT. TY 12W WILL
IMMINENTLY EMBARK ON A GRADUAL, PROLONGED PERIOD OF WEAKENING.
ALTHOUGH IT BRIEFLY INTENSIFIED AFTER ITS LAST ERC, THE SYSTEM WILL
TRAVERSE OVER LOWER OHC, WHICH WILL BE INCAPABLE OF SUPPORTING A
STORM OF ITS CURRENT HIGH INTENSITY. WHILE OTHER ENVIRONMENTAL
FACTORS, SUCH AS LOWER VWS AND HIGH SST, WILL BE FAVORABLE, THE
DIMINISHING OHC WILL BE THE PRIMARY DRIVER OF THE SLOW DECAY.
CONSEQUENTLY, THE FORECAST LEVELS OFF THE WEAKENING TREND AT TAU
96. THE SYSTEM WILL LIKELY UNDERGO AT LEAST ONE ADDITIONAL ERC
BEFORE REACHING THE RYUKYU ISLANDS. THIS WILL RESULT IN AN EVEN
LARGER WIND FIELD AT TAU 96 AND TAU 120, CAUSING SIGNIFICANT
IMPACTS TO EXTEND FAR FROM THE STORM'S CENTER.

MODEL DISCUSSION: THE CROSS-TRACK SPREAD AMONG THE MODEL GUIDANCE
IS TIGHT AND BETTER THAN THE CLIMATOLOGICAL AVERAGE. HOWEVER, THE
ALONG-TRACK SPREAD INCREASES SIGNIFICANTLY IN THE EXTENDED PERIOD,
FROM 95 NM AT TAU 72 TO 290 NM AT TAU 120. THIS DIVERGENCE IS
DRIVEN BY DIFFERING FORWARD SPEEDS, WITH THE MORE POLEWARD TRACK
SOLUTIONS TENDING TO MOVE THE SYSTEM FASTER. THE GFS, NAVGEM, AND
GALWEM SOLUTIONS ARE SOUTH OF CONSENSUS AND THUS SLOWER, WHILE
ECMWF, THE ECENS AND GEFS ENSEMBLE MEANS, AND THE AI MODEL
CONSENSUS TRACKERS ARE FURTHER NORTH AND FASTER. THE JTWC FORECAST
TRACK IS VIRTUALLY UNCHANGED FROM THE LAST FORECAST, POSITIONED
WITH HIGH CONFIDENCE NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 60
AND THEN HEDGED POLEWARD OF CONSENSUS THROUGH TAU 120. THE
INTENSITY AIDS DEPICT GRADUAL WEAKENING THROUGH THE FORECAST
PERIOD, BUT WITH SIGNIFICANT SPREAD. COAMPS-TC IS THE HIGH-END
OUTLIER, DEPICTING RE-INTENSIFICATION TO 135 KTS. THIS SCENARIO IS
DISCOUNTED AS IT DOES NOT ALIGN WITH THE PREDICTED UPSTREAM
ENVIRONMENT. HAFS-A IS THE MOST AGGRESSIVE IN WEAKENING THE SYSTEM
DOWN TO 75 KTS BY TAU 120. THE HWRF AND EXPERIMENTAL GOOGLE
DEEPMIND MODELS DEPICT GRADUAL WEAKENING THROUGH TAU 72 WITH LITTLE
CHANGE IN INTENSITY THEREAFTER. THE JTWC INTENSITY FORECAST IS SET
WITH HIGH CONFIDENCE FOR THE FIRST 72 HOURS AND MEDIUM CONFIDENCE
FOR THE LATER PERIOD. IT DEPICTS GRADUAL WEAKENING IN CLOSEST
ALIGNMENT WITH THE HWRF AND DEEPMIND SOLUTIONS.

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