Advisories

WDPN31 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.0N 149.4E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 445 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:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CIRCULAR, 30 NM WIDE EYE EMBEDDED WITHIN A SYMMETRIC CENTRAL DENSE
OVERCAST (CDO) AND EXTENSIVE SPIRAL BANDS ALONG THE PERIPHERY. THE
OVERALL EXTENT OF THE COLDEST CLOUD TOPS HAS DECREASED AS THE CDO
ITSELF SHRINKS, THOUGH THE CONVECTION ALONG THE EYEWALL REMAINS
ENERGETIC. THIS CONVECTION IS SUPPORTED BY GOOD RADIAL OUTFLOW
ALOFT, INDICATING A LOW-SHEAR ENVIRONMENT. MULTIPLE RECENT PASSES
BY MICROWAVE SOUNDERS BETWEEN 021040Z AND 021543Z AND THE 021613Z
AMSR2 IMAGER CONFIRMS THAT AN OUTER, FRAGMENTED CONVECTIVE RING IS
ATTEMPTING TO CONSOLIDATE AROUND THE EYEWALL, FORESHADOWING THE
ONSET OF A FOURTH EYEWALL REPLACEMENT CYCLE (ERC). WHILE TYPHOON
(TY) 12W IS TRAVERSING OVER VERY WARM SEA SURFACE TEMPERATURES
(SST) OF 30-31 DEGREES CELSIUS, THE UNDERLYING SUB-SURFACE
TEMPERATURES ARE COOLER, RESULTING IN A LOWER OCEAN HEAT CONTENT
(OHC). THIS CONDITION INCREASES THE LIKELIHOOD OF FASTER UPWELLING
OF COOLER WATER, WHICH HAS LARGELY BEEN RESPONSIBLE FOR THE
DEGRADATION IN STRUCTURE. THE INITIAL POSITION IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE WELL-DEFINED, CLOUD-FREE EYE. AS THE
CONVECTIVE STRUCTURE CONTINUES TO DEGRADE, THE INITIAL INTENSITY
HAS BEEN LOWERED TO 105 KTS WITH MEDIUM CONFIDENCE, WHICH IS
SUPPORTED BY THE T5.0-6.0 FIXES AND THE DECREASING OBJECTIVE
ESTIMATES FROM CIMSS RANGING FROM 92 KTS TO 119 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 110 KTS AT 021500Z
   CIMSS ADT: 92 KTS AT 021800Z
   CIMSS AIDT: 95 KTS AT 021800Z
   CIMSS D-MINT: 112 KTS AT 021614Z
   CIMSS D-PRINT: 86 KTS AT 021800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 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 BEING STEERED WEST-NORTHWESTWARD BY
THE WESTERN EXTENSION OF A STR CENTERED NEAR 43N 175W. THIS PATTERN
WILL HOLD THROUGH TAU 48, GUIDING THE CENTER TOWARD A VERY CLOSE
PASSAGE TO IWO TO. AFTER TAU 48, THE PRIMARY STEERING INFLUENCE
WILL TRANSITION TO A SEPARATE STR CENTERED OVER THE KOREAN
PENINSULA, WHICH WILL MAINTAIN THE ESTABLISHED DIRECTION OF MOTION.
AS THE TYPHOON APPROACHES THE RYUKYU ISLANDS, ITS FORWARD MOTION
WILL DECREASE FROM 12-13 KTS AT TAU 48 TO 08 KTS AT TAU 120. THIS
DECELERATION WILL BE CAUSED BY A LARGE CYCLONE PASSING OVER EASTERN
SIBERIA, WHICH WILL FLATTEN THE STEERING RIDGE AND RESULT IN A
WEAKER STEERING GRADIENT. TY 12W IS NOW ON A GRADUAL WEAKENING
TREND THAT WILL PERSIST THROUGHOUT ITS JOURNEY WESTWARD. WHILE SOME
ENVIRONMENTAL FACTORS FOR TY 12W WILL BE FAVORABLE, SPECIFICALLY VERY
WARM SST AND LOW VERTICAL WIND SHEAR, THE ERC AND LOWER OHC WILL BE
THE MAIN LIMITING FACTORS, LEADING TO SLOW DEGRADATION OF THE
CONVECTIVE STRUCTURE. THE ERC WILL DEGRADE THE INNER CORE AS THE
OUTER RING CONSOLIDATES, AND THE LOWER OHC WILL BE INCAPABLE OF
SUPPORTING A STORM OF HIGH INTENSITY. IT IS WORTH NOTING THAT,
BECAUSE OF THE LARGE INNER CORE, THE ERC WILL BE SLOW AND MORE
SUSCEPTIBLE TO INTERRUPTIONS FROM ENVIRONMENTAL EFFECTS. SHOULD THE
ERC BEGIN IN EARNEST, IT FACES A HIGHER LIKELIHOOD OF BECOMING A
PARTIAL OR STALLED EVENT AND LIKELY WILL NOT COMPLETE PRIOR TO TAU
60. CONSEQUENTLY, A PROLONGED WEAKENING TREND IS PREDICTED OUT TO
TAU 96. THE ERC WILL LEAD TO STRUCTURAL CHANGES THAT WILL EXPAND
THE WIND FIELD EVEN FURTHER, CAUSING HAZARDS TO EXTEND FAR FROM THE
STORM CENTER.

MODEL DISCUSSION: THE TRACK GUIDANCE IS VERY TIGHTLY PACKED THROUGH
TAU 120, WITH THE AI MODEL CONSENSUS POSITIONED NEAR THE GLOBAL AND
MESOSCALE PHYSICS-BASED MODELS. HAFS-A AND HWRF ANCHOR THE POLEWARD
SIDE OF THE UNCERTAINTY ENVELOPE, WHILE NAVGEM AND JGSM BOUND THE
EQUATORWARD EDGE. THE JTWC FORECAST TRACK IS VERY SIMILAR TO THE
PREVIOUS, ALIGNED NEAR THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE. A PRIMARY FORECAST CHALLENGE RELATES TO THE TRANSLATION
SPEED OF TY 12W IN THE EXTENDED PERIOD. THE ALONG-TRACK SPREAD
INCREASES FROM 125 NM AT TAU 72 TO 280 NM BY TAU 120. THIS SPREAD
IS ATTRIBUTED TO DIFFERING MODEL SOLUTIONS CORRESPONDING TO THE
EVOLUTION OF THE STR OVER THE KOREAN PENINSULA. FASTER MODELS LIKE
ECMWF SHOW A STRONGER, MORE PERSISTENT RIDGE, WHILE THE SLOWER
SOLUTIONS LIKE GFS DEPICT A MORE SIGNIFICANT FLATTENING OF THE
RIDGE. THE CONSENSUS POINTS AT TAU 96 AND TAU 120 LIE NEARLY
HALFWAY BETWEEN THESE TWO SCENARIOS. THE SPREAD IS ALSO QUITE LARGE
AMONG THE INTENSITY AIDS. COAMPS-TC REMAINS THE LONE OUTLIER IN
DEPICTING SIGNIFICANT INTENSIFICATION TO 140 KTS. THIS SOLUTION WAS
DISCOUNTED. EVERY OTHER RELIABLE INTENSITY AID SHOWS SLOW TO STEADY
WEAKENING THROUGH TAU 96. THE JTWC INTENSITY FORECAST ALIGNS WITH
THIS WEAKENING SCENARIO WITH MEDIUM CONFIDENCE FOR THE FIRST 72
HOURS. A NOTABLE DEVELOPMENT HAS EMERGED AT TAU 120. HAFS-A
PREDICTS RAPID INTENSIFICATION OF TY 12W BEGINNING AT TAU 96,
BRINGING THE SYSTEM BACK OVER 100 KTS BY TAU 120 AS THE SYSTEM
GRAZES OKINAWA. THIS SUGGESTS A POTENTIAL FOR THE ERC TO FINISH AND
THE INNER CORE TO TIGHTEN UP. FOR NOW, THE JTWC ALIGNS WITH THE
STEADY-STATE TRENDS OF THE EXPERIMENTAL GOOGLE DEEPMIND, HWRF, AND
GFS 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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