Advisories

WDPN31 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.1N 154.9E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 766 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 52 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
FOLLOWING THE COMPLETION OF A LONG-LASTING EYEWALL REPLACEMENT
CYCLE THAT PERSISTED FOR NEARLY 36 HOURS, TYPHOON (TY) 12W NOW
EXHIBITS A LARGE, 30 NM WIDE EYE. THIS FEATURE IS EMBEDDED IN A
LARGELY SYMMETRIC CENTRAL DENSE OVERCAST WITH CLOUD TOPS OF -70 TO
-80 DEGREES CELSIUS. ON INFRARED SATELLITE IMAGERY ENHANCED VIA THE
BD CURVE, THE CDO PRESENTS AS A SOLID, IMPRESSIVE RING OF WHITE
SHADES WITH SOME EMBEDDED CMG SHADES WRAPPING AROUND THE LARGE EYE.
A 011530Z AMSR2 89 GHZ IMAGE CLEARLY SHOWS THE LARGE, PRIMARY
EYEWALL AND AN OUTER CONVECTIVE BAND ON THE WESTERN PERIPHERY. THE
SYSTEM IS LOCATED IN A REGION OF LOW, SOUTHEASTERLY VERTICAL WIND
SHEAR (VWS) OF 10-15 KTS, WHICH IS ENABLING GOOD OUTFLOW ALOFT.
THIS IS COUPLED WITH VERY WARM SEA SURFACE TEMPERATURES (SST) AND
MODERATE OHC, CREATING CONDITIONS CONDUCIVE TO MAINTAINING A STRONG
TYPHOON. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE WELL-DEFINED EYE. BASED ON THE IMPROVED CONVECTIVE
SIGNATURE SINCE ERC COMPLETION, THE INITIAL INTENSITY HAS BEEN
RAISED TO 125 KTS WITH MEDIUM CONFIDENCE. THIS ASSESSMENT IS
SUPPORTED BY THE INCREASING OBJECTIVE ESTIMATES FROM CIMSS RANGING
FROM 115 KTS TO 130 KTS AND THE SUBJECTIVE DVORAK FIXES OF T6.5
FROM PGTW, KNES, AND RCTP.

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: T6.5 - 127 KTS
   CIMSS SATCON: 128 KTS AT 011530Z
   CIMSS ADT: 115 KTS AT 011800Z
   CIMSS AIDT: 115 KTS AT 011800Z
   CIMSS D-MINT: 124 KTS AT 011603Z
   CIMSS D-PRINT: 118 KTS AT 011800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 12W IS GRADUALLY TURNING WESTWARD AT 13
KTS, DRIVEN BY AN AMPLIFYING STR TO ITS NORTHEAST. FOR THE NEXT 48
HOURS, THE WESTERN EXTENSION OF THIS RIDGE WILL STEER THE SYSTEM ON
A WEST-NORTHWESTWARD TRAJECTORY. IN THE LATTER PART OF THE FORECAST
PERIOD, A SEPARATE LARGE RIDGE POSITIONED OVER THE KOREAN PENINSULA
WILL BECOME THE DOMINANT STEERING MECHANISM, MAINTAINING THE
WESTWARD MOTION AND FORCING THE SYSTEM TO PASS VERY NEAR IWO TO. AS
TY 12W APPROACHES OKINAWA, THE FORWARD SPEED WILL GRADUALLY
DECREASE TO 10 KTS. THIS SLOWING WILL BE INDUCED BY A LARGE CYCLONE
DEVELOPING OVER EASTERN SIBERIA, WHICH WILL ERODE STR AND RESULT
INTO A WEAKER STEERING GRADIENT. THE TYPHOON HAS SLIGHTLY
INTENSIFIED OVER THE PAST 6 HOURS AFTER THE COMPLETION OF AN ERC.
HOWEVER, THE OCEANIC ENVIRONMENT AHEAD OF THE SYSTEM WILL BECOME
LESS CONDUCIVE FOR SUPPORTING SUCH AN INTENSE STORM. WHILE THE SST
WILL REMAIN VERY WARM AT 29-31 DEGREES CELSIUS THROUGH TAU 120, THE
OHC WILL DROP TO BELOW 100 KJ PER CM2. THIS WILL BE THE PRIMARY
DRIVER OF A GRADUAL WEAKENING TREND THROUGH THE FORECAST PERIOD.
HIGH-RESOLUTION MESOSCALE MODELS INDICATE THAT ONE ADDITIONAL ERC
IS POSSIBLE BEFORE THE SYSTEM REACHES THE RYUKYU ISLANDS. THE ERC
WILL LEAD TO A FURTHER EXPANSION OF THE WIND FIELD, WHICH IS
FACTORED INTO THE EXTENDED FORECAST AT TAU 96 AND TAU 120.

MODEL DISCUSSION: THE TRACK GUIDANCE ENVELOPE IS QUITE TIGHT, WITH
THE SPREAD AMONG THE INDIVIDUAL MODELS BEING BETTER THAN THE
CLIMATOLOGICAL AVERAGE. THE SOLUTIONS FROM THE PHYSICS-BASED
DETERMINISTIC MODELS, THE AI MODELS, AND THE ENSEMBLE MEANS ARE ALL
CLUSTERED TOGETHER, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST
TRACK, WHICH IS PLACED NEAR THE MULTI-MODEL CONSENSUS. THE FORECAST
CHALLENGE RELATES TO THE STORM'S FORWARD SPEED IN THE EXTENDED
PERIOD. THE ALONG-TRACK SPREAD NOTABLY EXPANDS FROM 150 NM AT TAU
96 TO 250 NM AT TAU 120. THIS DIVERGENCE IS DUE TO TRACK SPEED,
WITH POLEWARD SOLUTIONS MOVING FASTER THAN THE EQUATORWARD ONES.
THE FORECAST POINT AT TAU 120 LIES BETWEEN THE FASTER ECMWF AND THE
SLOWER GFS AND HAFS-A SOLUTIONS. THE MAJORITY OF THE INTENSITY AIDS
DEPICT SLOW WEAKENING THROUGH THE ENTIRE FORECAST PERIOD. HOWEVER,
SIGNIFICANT SPREAD EXISTS AMONG THE MODELS, CREATING A LARGE
UNCERTAINTY ENVELOPE IN THE EXTENDED. COAMPS-TC IS THE OUTLIER,
MAINTAINING 125-135 KTS FOR MOST OF THE FORECAST PERIOD.
CONVERSELY, HAFS-A IS THE MOST AGGRESSIVE IN WEAKENING THE SYSTEM.
THE JTWC INTENSITY FORECAST CLOSELY TRACKS WITH THE CONSENSUS
THROUGH TAU 36. FROM TAU 48 TO TAU 120, IT HEDGES BETWEEN THE
WEAKER HAFS-A SOLUTION AND THE STRONGER MULTI-MODEL CONSENSUS WITH
LOW CONFIDENCE.

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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