Tropical Storm HINNAMNOR Advisory Mi, 31.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 12W (HINNAMNOR) WARNING NR
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.9N 130.3E
   INITIAL INTENSITY: 135 KTS
   GEOGRAPHIC REFERENCE: 139 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A COMPACT
SYSTEM SHOWING SIGNS OF WEAKENING, WITH SOME EROSION OF THE OUTER
SECTIONS OF THE CDO, PARTICULARLY ON THE WEST SIDE. A SERIES OF
RECENT MICROWAVE PASSES AS WELL AS ANIMATED RADAR IMAGERY CONFIRM
ON ONGOING EYEWALL REPLACEMENT CYCLE (ERC), WITH THE RADAR IN
PARTICULAR SHOWING A WELL DEFINED INNER EYEWALL, A SIZEABLE MOAT
AND SECONDARY EYEWALL ABOUT 35NM OUT FROM THE CENTER. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON A 7NM EYE IN THE
VISIBLE IMAGERY AND RADAR CENTER FIXES. A 302110Z SENTINEL-1B
SYNTHETIC APERTURE RADAR (SAR) BULLSEYE SHOWED A RING OF WINDS AT
OR ABOVE 125 KNOTS SURROUNDING THE EYE, WITH A MAXIMUM MEASUREMENT
OF 145 KNOTS. SINCE THIS OCCURRED AT OR NEAR THE PEAK AND PRIOR TO
THE FULL IMPACT OF THE ERC, THE DATA PROVIDES HIGH CONFIDENCE IN
THE INITIAL INTENSITY ASSESSMENT OF 135 KNOTS, CONSISTENT WITH THE
BULK OF THE DVORAK CURRENT INTENSITY ESTIMATES AND THE SATCON.
ANALYSIS REVEALS THE MAJORITY OF THE OUTFLOW IS RADIAL BUT CONFINED
TO THE IMMEDIATE REGION OF THE SYSTEM ITSELF, EXCEPT TO
EQUATORWARD, WHERE THE OUTFLOW IS EXPANDING. THE INITIAL WIND RADII
HAVE BEEN ADJUSTED SLIGHTLY SMALLER BASED ON THE SAR DATA.
INITIAL WIND RADII BASIS: SAR DATA
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A MID TO
UPPER-LEVEL RIDGE.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T7.0 - 140 KTS
   RJTD: T7.0 - 140 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 137 KTS AT 302129Z
   CIMSS ADT: 127 KTS AT 302340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: STY 12W IS TRACKING ALONG THE SOUTHERN SIDE OF
A THIN RIDGE, PRIMARILY IN THE MID TO UPPER-LEVELS, AS STEERING
TRANSITIONS FROM THE SUBTROPICAL RIDGE (STR) TO THE NORTHEAST TO A
BUILDING STR TO THE WEST OVER SOUTHERN CHINA. THE SYSTEM WILL
CONTINUE TRACKING WEST-SOUTHWEST THROUGH TAU 12, THEN GRADUALLY
TURN MORE SOUTHWARD AS THE INFLUENCE OF THE STR TO THE WEST
INCREASES AND THE SYSTEM UNDERGOES BINARY INTERACTION WITH TD 13W,
CURRENTLY APPROXIMATELY 400NM TO THE SOUTH BUT CLOSING RAPIDLY. THE
COMBINATION OF THE ENHANCED STEERING GRADIENT TO THE WEST AND TD
13W WILL DRIVE THE SYSTEM SOUTH-SOUTHWESTWARD THROUGH TAU 36.
SIGNIFICANT UNCERTAINTY ENTERS INTO THE DISCUSSION AFTER TAU 36, AS
THE SYSTEM ENTERS A WEAK STEERING PATTERN, NESTED BETWEEN COMPETING
RIDGES TO THE WEST AND EAST, AND A NEAR EQUATORIAL RIDGE (NER)
BUILDING IN TO THE SOUTH, LEADING TO QUASI-STATIONARY MOVEMENT
BETWEEN ROUGHLY TAU 36 TO TAU 60. AROUND TAU 48, A MID-LATITUDE
MAJOR SHORTWAVE TROUGH WITH STRONG DYNAMIC FORCING WILL BEGIN TO
DEVELOP OVER FAR NORTHWEST CHINA, AND BEGIN TO ERODE THE WESTERN
RIDGE, WHILE THE ENHANCED SOUTHWEST MONSOONAL FLOW PUMPING WARM AIR
POLEWARD TO THE EAST WILL BUILD A STRONG RIDGE ALONG THE 140TH
MERIDIAN. THESE EFFECTS WILL CONTINUE TO STRENGTHEN UNTIL TAU 72,
WHEN THE EASTERN RIDGE WILL ASSUME THE DOMINANT STEERING ROLE, AND
KICK STY 12W OUT OF THE NEST, AND IT WILL ACCELERATE NORTHWARD INTO
THE EAST CHINA SEA THROUGH THE REMAINDER OF THE FORECAST PERIOD.
DUE TO THE ONGOING ERC, THE SYSTEM IS BEGINNING TO WEAKEN. THE ERC,
INCREASING SHEAR, AND SIGNIFICANT UPWELLING, PARTICULARLY AFTER TAU
36, MEAN THAT STY 12W WILL BE UNLIKELY TO ATTAIN ITS PREVIOUS GLORY
AFTER COMPLETION OF THE ERC. THE SYSTEM IS FORECAST TO STEADILY
WEAKEN THROUGH TAU 72, DOWN TO A MINIMUM OF 95 KNOTS. AS THE SYSTEM
MOVES BACK OVER OPEN OF THE ECS, SHEAR LOOKS TO REDUCE AGAIN AND
THE SYSTEM IS FORECAST TO REINTENSIFY ONCE MORE AS UPPER-LEVEL
OUTFLOW DRAMATICALLY IMPROVES.
MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
24 BUT THEN DIVERGES INTO TWO DISTINCT GROUPINGS. CONSISTENT WITH
THE PREVIOUS RUNS, THE UKMET, GALWEM, EGRR, NAVGEM AND UKMET
ENSEMBLE AGREE ON A FURTHER SOUTHWARD TRACK, THEN TAKE THE SYSTEM
OVER TAIWAN AND INTO EASTERN CHINA. MEANWHILE THE GFS, ECMWF, HWRF,
JGSM AND THEIR ENSEMBLES AGREE ON A SLIGHTLY MORE NORTHWARD DIP,
AND A SHARP TURN POLEWARD BUT WITH SIGNIFICANT ALONG-TRACK SPREAD
AFTER TAU 96. THE CONSENSUS MEAN IS BEING PULLED TOO FAR TO THE
WEST AND SPLITS THE MIDDLE OF THE BIFURCATION. THE JTWC FORECAST
REMAINS CONSISTENT WITH THE PREVIOUS FORECAST OVERALL, BUT LIES A
BIT FURTHER EAST AFTER TAU 72 AND SLIGHTLY FASTER AT TAU 120. THE
FORECAST LIES CLOSEST TO THE ECMWF SOLUTION. WHILE CONFIDENCE IS
HIGH IN THE SHORT-TERM, IT QUICKLY DECREASES TO LOW DUE TO THE
UNCERTAINTY IN THE QUASI-STATIONARY (QS) PERIOD AND THE BIFURCATION
IN THE POST-QS TRACK. INTENSITY GUIDANCE IS IN OVERALL GOOD
AGREEMENT THROUGH THE FORECAST PERIOD WITH ALL MODELS CONSTRAINED
WITHIN A 20-30 KNOT ENVELOPE THROUGH THE DURATION OF THE FORECAST.
THE COAMPS-TC ENSEMBLE (RAPID INTENSIFICATION) PROBABILITIES ARE
PICKING UP ON AN INCREASED POTENTIAL FOR RI IN THE LATER TAUS, WITH
A 40 PERCENT PROBABILITY NOW INDICATED AFTER TAU 96. THE JTWC
FORECAST REMAINS CONSISTENT WITH BOTH THE CONSENSUS MEAN AND THE
PREVIOUS FORECAST WITH LOW CONFIDENCE IN THE LONG-RANGE FORECAST.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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