Advisories

WDPN31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2N 158.3E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 1718 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
WELL-DEFINED, CLOUD-FREE EYE EMBEDDED WITHIN A CENTRAL DENSE
OVERCAST WITH A RAGGED CANOPY. THE CONVECTIVE ACTIVITY SURROUNDING
THE EYEWALL REMAINS ROBUST, EXHAUSTING OUTWARD IN ALL DIRECTIONS.
THE ENVIRONMENT IS HIGHLY FAVORABLE, CHARACTERIZED BY HIGH OHC AND
LOW VERTICAL WIND SHEAR (VWS). THE DOMINANT FACTOR PREVENTING
INTENSIFICATION IS AN EYEWALL REPLACEMENT CYCLE (ERC) THAT APPEARS
TO BE NEARING COMPLETION. A COMPARISON OF THE 311931Z AND 312118Z
SSMIS 91 GHZ MICROWAVE IMAGES CONFIRMS THIS, REVEALING THAT THE
INNER EYEWALL IS ERODING AWAY WHILE THE OUTER CONVECTIVE RING
CONSOLIDATES INTO THE NEW PRIMARY EYEWALL. THIS CONCLUSION IS
FURTHER SUPPORTED BY A VISIBLE SHALLOWING OF THE INNER EYEWALL AS
OBSERVED ON THE MSI. A SENTINEL-1C SAR PASS AT 311916Z ESTIMATED
PEAK WINDS OF 106 KTS, WHICH IS CONSIDERED AN UNDERESTIMATE. A
312205Z ASCAT-B PASS INDICATES THAT THE WIND FIELD HAS EXPANDED,
WITH GALE-FORCE WINDS NOW EXTENDING OUTWARD TO 200 NM FROM THE
CENTER. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE CIRCULAR EYE. DUE TO THE TRANSITIONAL STATE OF THE STORM
DURING ERC, THE INITIAL INTENSITY IS HELD AT 125 KTS WITH LOW
CONFIDENCE, WHICH IS SLIGHTLY ABOVE THE OBJECTIVE ESTIMATES FROM
CIMSS RANGING FROM 115 KTS TO 123 KTS BUT ALIGNS WELL WITH THE T6.5
SUBJECTIVE DVORAK FIXES FROM PGTW, KNES, RJTD, AND RCTP.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF AN EXPANSIVE,
DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 122 KTS AT 312230Z
   CIMSS ADT: 119 KTS AT 010010Z
   CIMSS AIDT: 115 KTS AT 010010Z
   CIMSS D-MINT: 123 KTS AT 312118Z
   CIMSS D-PRINT: 120 KTS AT 010010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   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 CONTINUE ON A NORTHWESTWARD
TRAJECTORY, STEERED ALONG THE SOUTHWESTERN PERIPHERY OF A STR
CENTERED NEAR 40N 177E. AS A LONGWAVE TROUGH EXTENDING SOUTH OF THE
KAMCHATKA PENINSULA LIFTS POLEWARD, THE WESTERN EXTENSION OF THE
STR WILL BUILD WESTWARD. THIS WILL FORCE A GRADUAL TURN TOWARD THE
WEST. BY TAU 60, A LARGE RIDGE CENTERED OVER THE KOREAN PENINSULA
WILL BECOME THE PRIMARY STEERING INFLUENCE, MAINTAINING THIS
WESTWARD MOTION TOWARD THE RYUKYU ISLANDS THROUGH TAU 120. THE
SYSTEM IS APPROACHING THE END OF ITS WINDOW OF OPPORTUNITY TO
INTENSIFY. TY 12W WILL BE MOVING INTO A LESS FAVORABLE ENVIRONMENT
OF LOWER OHC AND HIGHER SHEAR IN ABOUT 6-12 HOURS. WHILE THE ERC
WILL COMPLETE IMMINENTLY, THE KEY SHORT-TERM CHALLENGE IS
DETERMINING IF THE SYSTEM HAS ENOUGH TIME TO RE-INTENSIFY BEFORE
THE ENVIRONMENT DEGRADES. THE FORECAST CALLS FOR A BRIEF PERIOD OF
SLIGHT INTENSIFICATION IMMEDIATELY FOLLOWING THE ERC, AFTER WHICH A
SLOW BUT STEADY WEAKENING TREND WILL COMMENCE FROM TAU 24 TO TAU
120 AS THE LESS FAVORABLE CONDITIONS TAKE HOLD. IT IS IMPORTANT TO
NOTE THAT SUBSEQUENT ERC EVENTS ARE LIKELY IN THE EXTENDED PERIOD.
THESE EVENTS, WHICH ARE DIFFICULT TO TIME, WILL INTRODUCE LESS
PREDICTABLE FLUCTUATIONS IN INTENSITY. THE IMPACT OF THESE FUTURE
CYCLES WILL BE THE CONTINUED EXPANSION OF THE STORM'S WIND FIELD,
CAUSING HAZARDS TO EXTEND FURTHER FROM THE CENTER EVEN AS THE
INTENSITY WANES.

MODEL DISCUSSION: MODELS REMAIN IN VERY TIGHT AGREEMENT, YIELDING
UNCERTAINTY THAT IS BELOW THE CLIMATOLOGICAL AVERAGE. NAVGEM AND
GFS REPRESENT THE EQUATORWARD OUTLIERS, WHILE HWRF IS THE MOST
POLEWARD MODEL. THE CORE GUIDANCE ENVELOPE, WHICH CONTAINS A TIGHT
CLUSTERING OF AI AND PHYSICS-BASED MODELS, GIVES HIGH CONFIDENCE IN
THE OVERALL TRACK PHILOSOPHY. ALL MODELS CONCUR ON A WESTWARD TURN.
HOWEVER, THE SYSTEM'S TRANSLATION SPEED BEYOND TAU 96 DRIVES THE
PRIMARY UNCERTAINTY IN TIMING IN THE EXTENDED PERIOD. THE
ALONG-TRACK SPREAD, WHICH IS TIGHT THROUGH TAU 96, INCREASES
SUBSTANTIALLY TO 220 NM AT TAU 120. THE JTWC FORECAST TRACK IS
POSITIONED ALONG THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.
THE INTENSITY GUIDANCE SUITE EXHIBITS SIGNIFICANT SPREAD, CREATING
CONSIDERABLE UNCERTAINTY. IN THE NEAR-TERM, THE HAFS-A, HWRF, AND
EXPERIMENTAL GOOGLE DEEPMIND SOLUTIONS DEPICT A NEARLY STEADY
INTENSITY THROUGH TAU 12, FOLLOWED BY SLOW WEAKENING. BEYOND 36
HOURS, HAFS-A NOTABLY PREDICTS MORE RAPID WEAKENING TO 85 KTS BY
TAU 60 AND 65 KTS BY TAU 120, WHILE COAMPS-TC MAINTAINS THE SYSTEM
AT 130 KTS FOR THE ENTIRE PERIOD. THE JTWC INTENSITY FORECAST IS
SET WITH MEDIUM CONFIDENCE IN THE SHORT TERM, BUT, GIVEN THIS
UNCERTAINTY, LOW CONFIDENCE IS GIVEN TO THE EXTENDED PERIOD. THE
FORECAST ALLOWS FOR A BRIEF OPPORTUNITY FOR TY 12W TO REGAIN SUPER
TYPHOON STATUS BEFORE ALIGNING WITH THE MAJORITY OF RELIABLE AIDS
AND COMMENCING A STEADY DOWNWARD TREND.

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