Advisories

WDPN31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.2N 140.6E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 695 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 12W (DOLPHIN) CONTINUES TO OUTPERFORM EXPECTATIONS,
MAINTAINING A COMPACT INNER CORE OF DEEP CONVECTION AND A SYMMETRIC 
BUT THIN EYEWALL AND A 17NM WIDE EYE FEATURE. THE EYE IS SUFFICIENTLY
CLOUD-FREE TO MAINTAIN A 17C EYE TEMPERATURE WHILE MULTIPLE
MESOVORTICES ARE VISIBLE, EVEN IN THE SHORTWAVE INFRARED (SWIR)
LOOP. RELATIVELY DRY MID-LEVEL AIR IS CLEARLY ENTRAINED ALONG THE 
EASTERN SIDE OF THE CIRCULATION, NOW WRAPPING AROUND TO THE WESTERN 
FLANK, PRODUCING A CLEAR MOAT FEATURE. THESE FEATURES WERE BECOMING 
EVIDENT IN A 040748Z WSF-M 89GHZ MICROWAVE IMAGE, ALONG WITH A 
THINNING AND EROSION OF THE NORTHWESTERN EYEWALL, LIKELY DUE TO 
ELEVATED NORTHWESTERLY UPPER-LEVEL SHEAR AND SOME DRY MID-LEVEL AIR 
IN THAT QUADRANT. A 040842Z RCM-3 SAR PASS REVEALED A VMAX (PEAK) OF 
115 KNOTS, AND A VMAX (MEAN) OF 106 KNOTS, SUPPORTING THE 0600Z 
INTENSITY ESTIMATE OF 115 KNOTS WITH HIGH CONFIDENCE. THE SAR ALSO 
DEPICTED A PATCH OF LIGHTER (40-50 KNOTS) WINDS IN THE SOUTHEASTERN 
QUADRANT, WHICH IS BACKED UP BY THE SAME FEATURE IN THE 041152Z 
ASCAT-B PASS. BOTH SENSORS ALSO INDICATED THE CONTINUED EXPANSION OF 
THE ALREADY VERY LARGE WIND FIELD. THE INITIAL POSITION IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON THE 17NM WIDE EYE IN THE EIR. THE 
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN 
EXTRAPOLATION OF THE EARLIER SAR DATA, SUPPORTED BY AN AVERAGING OF 
THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES AND THE CIMSS ADT AND 
AIDT-V2 ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS REMAIN 
OVERALL FAVORABLE, CHARACTERIZED BY STRONG RADIAL OUTFLOW ALOFT AND 
LOW DEEP-LAYER SHEAR. WHILE SSTS IN THE REGION ARE THE HIGHEST OF 
ANYWHERE IN THE WESTERN NORTH PACIFIC, THE WARM LAYER IS THIN, WITH 
LOW OHC AND THE EXPANSIVE WIND FIELD IS INDUCING OCEANIC UPWELLING 
ACROSS A VAST EXPANSE. THIS IS LEADING TO AN OVERALL REDUCTION IN 
SSTS NEAR THE CORE OF THE SYSTEM AND CERTAINLY IN THE EASTERN AND 
NORTHERN PORTIONS, MARGINALLY OFFSETTING THE OTHERWISE FAVORABLE 
CONDITIONS. ADDITIONALLY, MODEL-BASED SOUNDINGS SUGGEST A LAYER OF 
ENHANCED (10-15 KTS) NORTHWESTERLY SHEAR IN THE MID- TO UPPER-LEVELS.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA.  

CURRENT STEERING MECHANISM: SOUTHEASTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER THE NORTH-CENTRAL SEA OF
JAPAN (SOJ). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 109 KTS AT 041230Z
   CIMSS AIDT: 110 KTS AT 041230Z
   CIMSS D-PRINT: 91 KTS AT 041230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: MODERATE EASTWARD OUTFLOW CHANNEL ALONG 33N
LATITUDE, AT THE BASE OF AN UPPER-LEVEL TROUGH TO THE NORTHEAST;
UPWELLING OF COOLER SUBSURFACE WATERS. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 CONTINUES TO EXHIBIT OCCASIONAL TROCHOIDAL 
MOTION, PARTICULARLY AFTER IT PASSED OVER NORTH IWO TO ISLAND, BRIEFLY 
TRACKING WEST-SOUTHWESTWARD BEFORE RECENTLY RESUMING A MORE WEST-
NORTHWESTWARD TRACK. THE TRACK MADE GOOD OVER THE PAST SIX HOURS HAS 
BEEN JUST SOUTH OF DUE WEST, AT 12 KNOTS, MOVING ALONG THE SOUTHERN 
PERIPHERY OF A DEEP-LAYER STR WHICH IS CENTERED ANOMALOUSLY NORTH IN 
THE SEA OF JAPAN. EVEN THOUGH EVEN THOUGH TROCHOIDAL OSCILLATIONS ARE 
EXPECTED TO CONTINUE, THE OVERALL TRACK WILL REMAIN WEST-NORTHWESTWARD 
AT A FAIRLY STEADY 10-12 KNOTS THROUGH TAU 48, WITH THE SYSTEM PASSING 
VERY CLOSE TO MINAMI DAITO JIMA BY THIS POINT IN THE FORECAST. BY TAU 
48, A DEEP UPPER-LEVEL TROUGH WILL MOVE INTO NORTHEASTERN MANCHURIA. 
THE TROUGH WILL CONTINUE MOVING EASTWARD THROUGH THE REMAINDER OF THE 
FORECAST PERIOD. WHILE IT DOES NOT EXTEND SOUTH BEYOND THE KOREAN 
PENINSULA, THE TROUGH WILL ERODE THE STR FROM THE WEST AND ALLOW FOR 
DEVELOPMENT OF A WEAKNESS IN THE RIDGE TO DEVELOP OVER KOREA. THIS WILL 
WEAKEN THE STEERING GRADIENT, ALLOWING TY 12W TO SLOW AS IT APPROACHES 
THE RYUKYU ISLANDS. TRACK SPEEDS SLOW TO JUST 4-5 KNOTS AFTER THE 
SYSTEM MOVES INTO THE EAST CHINA SEA. BY THE END OF THE FORECAST 
PERIOD, THE SYSTEM WILL BEGIN A GRADUAL TURN TOWARDS THE NORTHWEST AS 
IT BEGINS TO BE STEERED BY A BUILDING RIDGE OVER SOUTHERN JAPAN. TY 12W 
IS FORECAST TO MAKE LANDFALL ON OKINAWA NEAR TAU 72 BEFORE MOVING INTO 
THE EAST CHINA SEA. REGARDING INTENSITY, THE SYSTEM APPEARS TO HAVE 
REACHED A STEADY STATE, ACHIEVING BALANCE BETWEEN COMPETING 
ENVIRONMENTAL FACTORS. THE FORECAST CALLS FOR THE SYSTEM TO WEAKEN 
SLIGHTLY OVER THE NEXT 12 HOURS AND THEN MAINTAIN INTENSITY THROUGH TAU 
36 BEFORE EMBARKING ON A STEPWISE WEAKENING TREND THROUGH LANDFALL AT 
OKINAWA DUE PRIMARILY TO MARGINALLY LOWER SSTS FROM OCEANIC UPWELLING 
AS WELL AS A REDUCTION IN OUTFLOW ALOFT. AFTER TAU 72, THE SYSTEM WILL 
WEAKEN MORE RAPIDLY AS IT SLOWS DOWN AND UPWELLING BECOMES MORE 
SIGNIFICANT. WHILE THE INTENSITY IS FORECAST TO STEADILY DECREASE, THE 
WIND FIELD CONVERSELY IS EXPECTED TO CONTINUE ITS EXPANSION, WITH GALE-
FORCE WINDS EXPECTED TO COVER AN ALMOST 600NM DIAMETER SWATH OF THE 
EAST CHINA SEA BY TAU 120. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH TAU 48, 
WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD. BEYOND THIS POINT HOWEVER, 
THE CONSENSUS MEMBERS BEGIN TO DIVERGE CONSIDERABLY. THE GFS, JGSM AND 
NAVGEM CONTINUE TO BE THE PRIMARY OUTLIERS, FIRST DIPPING THE SYSTEM 
SOUTH OF OKINAWA AS EARLY AS TAU 60, BEFORE TURNING SHARPLY NORTHWARD 
DIRECTLY ON TOP OF OKINAWA AND ENDING UP NORTH OF OKINAWA BY TAU 120. 
WITH THIS MODEL RUN, THE ECMWF AND GEFS MEAN ALSO DIVERGE FROM THE 
PACK, AFTER TAU 72 WHERE THE RUN THE SYSTEM SOUTHWESTWARD TO NEAR THE 
COAST OF CHINA BY TAU 120. THE REMAINDER OF THE CONSENSUS, INCLUDING 
THE CONSENSUS MEAN, AND THE AI MODELS CONTINUE TO BE CONSTRAINED TO A 
TIGHTLY DEFINED ENVELOPE WHICH SHOWS A WEST-NORTHWESTWARD, DECELERATING 
TRACK, FROM TAU 72 TO TAU 120. THE JTWC FORECAST IS PLACED NEAR THE AI 
CONSENSUS MEAN THROUGH THE FORECAST PERIOD. INTENSITY GUIDANCE IS 
MIXED, WITH A FAIRLY WIDE RANGE IN FORECASTED INTENSITIES; THE CTCX 
MODEL CONTINUES TO SUPPORT INTENSIFICATION, UP TO 135 KNOTS BY TAU 36, 
WHILE THE HAFS-A DEPICTS A RAPID WEAKENING TO JUST 75 KNOTS BY TAU 48 
FOLLOWED BY RAPID INTENSIFICATION UP TO A PEAK NEAR 100 KNOTS JUST 
PRIOR TO LANDFALL ON OKINAWA. THE HWRF, EXPERIMENTAL GOOGLE DEEPMIND 
(GDM) AND CONSENSUS MEAN DEPICT A MORE LIKELY SCENARIO OF A GENERALLY 
FLAT OR SLIGHT WEAKENING TREND THROUGH TAU 72 FOLLOWED BY MORE RAPID 
WEAKENING THEREAFTER. THE JTWC FORECAST IS PLACED NEAR THE HAFS-A AND 
GDM TRACKERS WITH MEDIUM TO LOW CONFIDENCE. 

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