Advisories

WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.3N 139.3E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 625 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:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
12W (DOLPHIN) MAINTAINING A COMPACT INNER CORE WITH DEEP CONVECTION
AND A PERSISTENT 15 NM EYE. THE CONVECTIVE BANDS SURROUNDING THE
CORE HAVE NEITHER IMPROVED NOR DEGRADED SIGNIFICANTLY OVER THE PAST
6 HOURS, ALTHOUGH A MOAT OF DRIER AIR HAS ENCLOSED THE INNER EYEWALL 
FEATURE ALMOST ENTIRELY. A 041558Z AMSR-2 37GHZ IMAGE CORROBORATES A 
MOAT OF DRY AIR SURROUNDING THE CORE AND REVEALS THAT THE OUTER 
CONVECTIVE BANDS ARE DISCONTINUOUS, SUGGESTING THAT ANOTHER ATTEMPT AT 
AN EYEWALL REPLACEMENT CYCLE IS NOT LIKELY IMMINENT. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE CENTER OF THE EYE 
FEATURE IN THE IR IMAGERY, IN VERY CLOSE PROXIMITY TO AGENCY DVORAK 
FIXES. THE INITIAL INTENSITY OF 105 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE SLIGHT WEAKENING TREND DEPICTED BY AGENCY 
DVORAK FIXES AND CURRENT INTENSITY VALUES OF T5.5-T6.0. THE 
ENVIRONMENT IS CHARACTERIZED AS FAVORABLE, WITH WARM (29-30 C) SEA 
SURFACE TEMPERATURES, LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), AND 
ROBUST RADIAL OUTFLOW ALOFT. THE FAVORABLY ENVIRONMENTAL CONDITIONS 
ARE SLIGHTLY OFFSET BY UPWELLING OF COLDER WATER BELOW THE SYSTEM AND 
THE INTRODUCTION OF DRY AIR.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHEASTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE CENTERED OVER THE SEA OF JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 92 KTS AT 041800Z
   CIMSS ADT: 87 KTS AT 041800Z
   CIMSS AIDT: 105 KTS AT 041800Z
   CIMSS D-MINT: 111 KTS AT 041601Z
   CIMSS D-PRINT: 105 KTS AT 041730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: WEAK DRY AIR ENTRAINMENT FROM THE WEST

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: TYPHOON 12W CONTINUES ON A MOSTLY WESTWARD
TRACK WITH A NOTABLE TROCHOIDAL WOBBLE UNDER THE STEERING INFLUENCE
OF THE STR OVER THE SEA OF JAPAN. THE WEST-NORTHWESTWARD TRACK IS
FORECAST TO CONTINUE THROUGH TAU 72, THEN BEGIN TO TURN POLEWARD 
THROUGH THE REMAINDER OF THE FORECAST PERIOD AS THE SYSTEM APPROACHES 
THE STR AXIS AND SLOWS ITS SPEED OF ADVANCE. THE CPA OF TY DOLPHIN'S 
CENTER TO KADENA AB AROUND 070800Z REMAINS SMALL AT 8 NM, HOWEVER, 
IMPACTS FROM THE SYSTEM WILL BE APPARENT WELL BEFORE THEN AS THE GALE 
FORCE WIND FIELD IS EXPECTED TO EXTEND BEYOND 500 NM IN DIAMETER. 
AFTER THE SYSTEM PASSES OVER OKINAWA, THERE IS SOME UNCERTAINTY 
INTRODUCED IN THE NATURE OF THE RECURVE AS THE STEERING RIDGE WEAKENS 
AND SHIFTS EASTWARD. THE INTENSITY IS FORECAST TO WEAKEN SLOWLY AS 
WEAKENING OUTFLOW ALOFT AND UPWELLING OF COLDER WATER BELOW THE SYSTEM 
NEGATE THE OTHERWISE FAVORABLE ENVIRONMENT ALONG THE FORECAST TRACK.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ABOUT
THE WEST-NORTHWESTWARD TRACK THROUGH TAU 72, BUT THERE IS A CROSS-
TRACK SPREAD OF 90 NM AT THAT TIME WHICH COINCIDES WITH THE SYSTEM'S 
PASSAGE OVER OKINAWA. THE PRIMARY FACTOR RESULTING IN THIS SPREAD IS 
THE GROUP OF PHYSICS-BASED MODELS (NAVGEM, JGSM, AND GFS) THAT PREDICT 
A SHARP RECURVE SCENARIO IN THE LATER TAUS. THIS GROUP OF MODELS MAKE 
UP THE SOUTHERN EDGE OF THE TRACK GUIDANCE ENVELOPE. THE REMAINDER OF 
GUIDANCE, INCLUDING MOST OPERATIONAL AND EXPERIMENTAL AI MODELS, 
DEPICT A MUCH LESS SEVERE RECURVING TRACK AND GENERALLY FASTER TRACK 
SPEEDS. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL 
CONSENSUS, WHICH FAVORS THE LATTER MAJORITY OF GUIDANCE, WITH MEDIUM 
CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. MODEL 
INTENSITY GUIDANCE REMAINS MIXED WITH THE LATEST MODEL RUN, WITH CTCI 
AS A NOTABLE OUTLIER SUGGESTING A PERIOD OF INTENSIFICATION TO 120 KTS 
AT TAU 48. COTI AND HWRF ALSO DEPICT A MUCH LESS SIGNIFICANT 
PERIOD OF INTENSIFICATION BETWEEN TAU 36-48. THE REMAINDER OF GUIDANCE 
DEPICTS AN OVERALL WEAKENING TREND THROUGHOUT THE ENTIRE FORECAST 
PERIOD AND BALANCE THE OUTLIERS IN THE CONSENSUS. THE JTWC INTENSITY 
FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGHOUT THE FORECAST 
PERIOD, WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE 
THEREAFTER OWING TO THE UNCERTAINTY SURROUNDING THE RECURVE SCENARIO.

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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