Advisories

WDPN31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0N 145.7E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 240 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 12W STRUGGLING TO COMPLETE ITS FOURTH EYEWALL REPLACEMENT
CYCLE (ERC). THE CLOUD SHIELD IS BECOMING INCREASINGLY SPARCE, AND
THE INNER EYEWALL IS STILL IDENTIFIABLE BUT OPENING ON THE NORTHERN
SIDE. THE OUTER EYEWALL LOOKS NO BETTER DEFINED THAN IT DID 6 HOURS
AGO, THOUGH THE DRY SLOT IS GETTING LARGER AND NOW ENVELOPS NEARLY
THE ENTIRE INNER EYE WALL. ANIMATED EIR ALSO REVEALS THE COLDEST
DEEP CONVECTION IS NOW RESTRICTED TO THE EASTERN SEMICIRCLE. THE
ENVIRONMENT REMAINS FAVORABLE, CHARACTERIZED BY LOW (10-15 KTS)
VERTICAL WIND SHEAR (VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES
(SST), AND GOOD DIVERGENCE ALOFT. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE RAGGED EYE PRESENT IN ANIMATED
EIR. THE INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY
ESTIMATES LISTED BELOW.

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: T5.0 - 90 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS D-PRINT: 88 KTS AT 031130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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: TY 12W (DOLPHIN) IS FORECAST TO CONTINUE
TRACKING ALONG THE SOUTHWESTERN EXTENSION OF THE STR CENTERED FAR
TO THE NORTHEAST. WITHIN THE NEXT 12-24 HOURS, THE STEERING
INFLUENCE WILL SHIFT TO A SECOND STR CURRENTLY CENTERED OVER THE
KOREAN PENINSULA. 12W WILL THEN TRACK WEST-NORTHWESTWARD ALONG THE
SOUTHERN PERIPHERY OF THAT RIDGE THROUGH THE END OF THE FORECAST
PERIOD. BETWEEN TAU 72-120, 12W MAY ENCOUNTER A WEAKER STEERING
ENVIRONMENT AS A DEEP-LAYER TROUGH PASSES NORTH OF THE STEERING
RIDGE AND WEAKENS IT, THEREBY REDUCING THE STEERING GRADIENT AND
POTENTIALLY SLOWING DOLPHIN'S SPEED OF ADVANCE. REGARDING
INTENSITY, 12W IS FORECAST TO MAINTAIN A RELATIVELY STEADY
INTENSITY THROUGHOUT THE FORECAST PERIOD. DOLPHIN IS EXPECTED TO
WEAKEN SLIGHTLY OVER THE NEXT 12 HOURS AS THE ERC CONTINUES, THEN
SUSTAIN AN INTENSITY OF APPROXIMATELY 85 KTS THROUGH TAU 96 AND
WEAKEN SLIGHTLY AFTER THAT, WITH THE 10-15 KTS OF VWS EXPECTED
TO REDUCE TO 5-10 KTS AFTER ABOUT TAU 24 AND THE OHC VALUES
DROPPING SLIGHTLY AROUND TAU 60-72. AS A RESULT, THE PRIMARY DRIVER
OF WEAKENING IN THE NEAR TERM FORECAST IS THE ERC. IN THE LIKELY
SCENARIO THAT DOLPHIN FAILS TO COMPLETE THE ONGOING ERC, IT WOULD
ACCELERATE THE RATE OF WEAKENING AND COMPOUND THE NEGATIVE EFFECTS
OF LOWER OHC. THE EYE AND WIND FIELD WILL REMAIN QUITE LARGE
THROUGH TAU 120, BRINGING IMPACTS TO THE ENTIRETY OF THE JAPANESE
RYUKYU ISLANDS REGARDLESS OF CENTER POSITION. 

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 120. THE ALONG-TRACK SPREAD HAS INCREASED
SLIGHTLY BY TAU 120, MEASURING 220 NM AT TAU 120. OF THE
MULTI-MODEL CONSENSUS MEMBERS, GFS AND GEFS ENSEMBLE MEAN ARE THE
SLOWEST MEMBERS AND ECMWF IS THE FASTEST. GFS IS DETECTING A MORE
SIGNIFICANT WEAKENING OF THE STEERING ENVIRONMENT AT THE END OF THE
FORECAST PERIOD, AND IS DEPICTING 12W GETTING CAUGHT IN A COL THAT
IS FORMED BY THE PASSING DEEP-LAYER TROUGH. THIS SCENARIO WOULD
CAUSE SLOWER TRACK SPEEDS THAN WHAT IS DEPICTED IN THE CURRENT
FORECAST. HOWEVER, ALL OTHER MULTI-MODEL CONSENSUS MEMBERS AND THE
EXPERIMENTAL AI MODELS DEPICT STEADY TRACK SPEEDS AS 12W CROSSES
THE RYUKYU ISLANDS. AS A RESULT, THE JTWC TRACK FORECAST IS NOT
SIGNIFICANTLY IMPACTED AND IS PLACED CLOSE TO THE MULTI-MODEL
CONSENSUS WITH OVERALL HIGH CONFIDENCE. RELIABLE INTENSITY AIDS ARE
IN GOOD AGREEMENT THROUGH TAU 120, WITH MOST MODELS DEPICTING A
STEADY INTENSITY WITH A SLIGHT WEAKENING TREND AFTER. HOWEVER, A FEW
MODELS ARE DEPICTING AN INTENSIFICATION PERIOD BEGINNING WITHIN THE
NEXT 12 HOURS. THIS IS UNLIKELY, BUT REMAINS A POSSIBILITY IF 12W
IS ABLE TO RECOVER FROM THE ERC. THEREFORE, THE JTWC INTENSITY
FORECAST IS ASSESSED WITH OVERALL LOW CONFIDENCE. THE JTWC INTENSITY
FORECAST LIES SLIGHTLY BELOW THE MULTI-MODEL CONSENSUS AND GFS, AND
CLOSE TO HAFS-A, HWRF, AND THE EXPERIMENTAL GOOGLE DEEPMIND. 

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