Tropical Storm HINNAMNOR Advisory Di, 30.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (HINNAMNOR) WARNING NR
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 26.8N 137.4E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 242 NM WEST-NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: WESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTI-SPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TIGHTLY
CURVED BANDING WRAPPING INTO A 8 NM DIAMETER EYE THAT HAS BECOME
PARTIALLY CLOUD-FILLED. CLOUD TOPS TEMPERATURES HAVE ALSO WARMED.
THE INITIAL POSITION WAS BASED ON THE EYE FEATURE IN MSI WITH HIGH
CONFIDENCE, AND SUPPORTED BY A 292141Z 91 GHZ SSMIS PASS THAT
REVEALS THE DEEP CONVECTIVE CORE AND A BANDING FEATURE ALONG THE
SOUTHEASTERN FLANK. THE INITIAL POSITION IS SLIGHTLY SOUTH OF TRUE
WEST, AND THE PRIOR FORECAST TRACK, WHICH OFFERS A SIGN THAT THE
SOUTHERN TRACK DIP AHEAD OF OKINAWA IS COMING TO FRUITION. ALTHOUGH
THE COARSE SSMIS DOES NOT RESOLVE THE INNER CORE STRUCTURE
COMPLETELY, THE MSI SUGGESTS AN EYEWALL REPLACEMENT CYCLE (ERC) IS
TAKING PLACE. THIS IS SUPPORTED BY CIMSS MPERC PROBABILITIES.
THE INTENSITY WAS LOWERED TO 115 KTS IN LIGHT OF THE OVERALL
DEGRADED APPEARANCE AND SUPPORTED BY A RANGE OF DVORAK CURRENT
INTENSITY ESTIMATES FROM T6.0 TO T6.5 (115 TO 127 KNOTS), WITH AN
ADT OF 115 KNOTS AT SATCON AT 121 KNOTS. ENVIRONMENTAL CONDITIONS
ARE HIGHLY FAVORABLE WITH RADIAL OUTFLOW, LOW VERTICAL WIND SHEAR
AND VERY WARM (29-30 DEGREE C) SST VALUES.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: DEEP-LAYERED EXTENSION OF THE
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T6.5 - 127 KTS
   RJTD: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 121 KTS AT 292142Z
   CIMSS ADT: 115 KTS AT 292340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
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 IS FORECAST TO CONTINUE TRACKING
QUICKLY WEST-SOUTHWESTWARD OVER THE NEXT 12-24 HOURS AS IT TRACKS
ALONG THE SOUTHERN PERIPHERY OF THE STR TO THE NORTH. AFTER TAU 24,
THE TRACK IS EXPECTED TO DEFLECT MORE EQUATORWARD AS A WESTERN STR
GRADUALLY TAKES OVER AS THE PREDOMINANT STEERING MECHANISM. BINARY
INTERACTION WITH INVEST 98W MAY ALSO PLAY A PART IN THIS SHIFT.
ENVIRONMENTAL FACTORS WILL REMAIN FAVORABLE, ALLOWING FOR A PERIOD
OF RE-INTENSIFICATION ONCE THE ERC COMPLETES. THE LATEST ROUND OF
MODEL GUIDANCE IS INCREASINGLY IN AGREEMENT WITH A MORE PRONOUNCED
SOUTHERLY SHIFT, WITH EVEN THE HWRF MODEL NOW KEEPING THE STRONGEST
CORE WINDS OFF OF OKINAWA. THIS NEW GUIDANCE ALSO HAS BACKED OFF THE
PEAK INTENSITY ESTIMATES, HOWEVER, 145 KNOTS WAS MAINTAINED THIS
CYCLE TO SEE IF THE TREND CONTINUES. BEYOND TAU 72, THE OUTLOOK
REMAINS VERY COMPLEX. A MIDLATITUDE SHORTWAVE TROUGH IS EXPECTED TO
DIG OVER THE KOREAN PENINSULA WHICH SHOULD PASS QUICKLY TO THE NORTH,
ERODING THE CURRENT STR AND CREATING A COMPETING STEERING SYNOPTIC
PATTERN, WITH A STR TO THE NORTHEAST AND WEST, AND A NEAR-EQUATORIAL
RIDGE TO THE SOUTH. THE SCENARIO RESULTS IN A PERIOD OF SLOW,
QUASI-STATIONARY (QS) MOTION. DURING THIS TIME, THE WIND FIELD IS
EXPECTED TO GROW SUBSTANTIALLY, WITH HWRF PREDICTING SIGNIFICANT
UPWELLING OF COOLER WATER. MODELS DIVERGE SHARPLY IN THE 96-120 TAU
RANGE. THE PRIMARY GROUPING OF MODELS TURNS 12W BACK TO THE NORTH TO
NORTHWEST ACROSS THE RYUKUS. THE MOST RECENT OFF- CYCLE ECMWF SOLUTION
IS NOW IN-LINE WITH THE BROADER GROUPING, LENDING CONFIDENCE THAT THE
EXTENDED TRACK WILL REMAIN WEST OF OKINAWA. THE AMOUNT OF TIME SPENT
QS OVER COOLER WATERS WILL HAVE A STRONG IMPACT ON LONG-RANGE
INTENSITY FORECAST, AND SHIPS GUIDANCE IS NOW INDICATING INCREASED
VERTICAL WIND SHEAR OF ABOUT 25 KNOTS AT TAU 72 AIDING IN THE
WEAKENING TREND. ALTHOUGH THERE IS STILL A SMALL GROUPING OF WESTWARD
MODELS, IT APPEARS THIS SOLUTION IS BECOMING LESS LIKELY, AS A
DOMINANT NUMBER OF TOTAL MEMBERS NOW TAKE THE TURN TO THE NORTH AFTER
TAU 72. DUE TO THE COMPETING STEERING, THERE IS HIGH UNCERTAINTY IN
THE EXACT TRACK OF THE CENTER. REGARDLESS, THE SYSTEM IS EXPECTED TO
TRANSITION INTO A LARGE SYSTEM AFTER TAU 72.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72 WITH APPROXIMATELY 125 NM SPREAD IN SOLUTIONS AT
THAT TIME. AFTER TAU 72, HOWEVER, DETERMINISTIC GUIDANCE DIVERGES AND
IS IN POOR AGREEMENT. ALL THE MODELS INDICATE THE SYSTEM WILL SLOW
AND BECOME QUASI-STATIONARY BUT DISAGREE ON WHERE THE SYSTEM WILL
WILL TRACK ONCE FORWARD MOTION RESUMES. ENSEMBLE GUIDANCE FAVORS A
SOLUTION THAT TURNS TYPHOON 12W BACK TO THE NORTH LEADING TO AN
EVENTUAL RE-CURVATURE SCENARIO. A SECONDARY GROUPING CONSISTING
PRIMARILY OF UKMET OFFICE-BASED MODEL GUIDANCE TRACKS HINNAMNOR
WESTWARD TOWARDS TAIWAN.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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