Tropical Storm HINNAMNOR Advisory 9月5日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (HINNAMNOR) WARNING NR 031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 28.6N 124.7E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 450 NM SOUTH-SOUTHWEST OF BUSAN, SOUTH
KOREA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SOMEWHAT RAGGED STRUCTURE OVERALL, THOUGH TY 12W HAS SUCCESSFULLY
MAINTAINED AN 8-NM EYE CENTERED WITHIN AN APPROXIMATELY 80-NM
DIAMETER CDO. OVERNIGHT MICROWAVE IMAGERY AND A 04XXXXZ AMSR2 91GHZ
IMAGE INDICATE EROSION OF THE LARGE SECONDARY EYEWALL THAT WAS
PRESENT YESTERDAY AS WELL AS THE EXTREMELY SMALL CONVECTIVE CORE OF
TY 12W, WHICH REMAINS RELATIVELY ISOLATED WITH LIMITED CONVECTIVE
BANDING. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE 8-NM IN THE EIR AND AGREEMENT OF AGENCY FIX POSITIONS.
REANALYSIS OF A 040934Z RADARSAT-2 SAR IMAGE RESULTED IN A SLIGHT
INCREASE OF THE 0600Z AND 1200Z INTENSITIES TO 110 KNOTS (THE SAR
FIX WAS 113 KNOTS), HEDGED ABOUT 5-10 KNOTS HIGHER THAN THE
SUBJECTIVE AND OBJECTIVE FIXES AT THAT TIME. NOT MUCH HAS CHANGED
IN THE FIX DATA OVER THE PAST 12 HOURS, WITH EXCUSIONS ABOVE AND
BELOW THE AVERAGE T5.5, BUT DUE THE COMPACT NATURE OF THE SYSTEM
AND PINHOLE EYE, DVORAK-BASED INTENSITY ESTIMATES ARE LIKELY A BIT
TOO LOW, SO THE INITIAL INTENSITY REMAINS SET AT 110 KNOTS,
EXTRAPOLATING FROM THE SAR FIX. THE SYSTEM IS MOVING GENERALLY
NORTHWARD BUT HAS SHOWN SOME FAIRLY EXTREME TROCHOIDAL MOTION OVER
THE PAST 6-12 HOURS AS IT WOBBLES ITS WAY NORTH. THE ENVIRONMENT
REMAINS FAVORABLE, WITH WARM SSTS AND LOW SHEAR (JUST 3 KNOTS IN
THE LATEST CIMSS ANALYSIS). ON TOP OF THAT, UPPER-LEVEL OUTFLOW HAS
EXPANDED TO THE WEST AND THE SYSTEM HAS NOW ESTABLISHED A POLEWARD
CHANNEL INTO THE NOSE OF STRONG JET MAX OVER THE BOHAI GULF. DRY
AIR INTRUSION FROM THE WEST IS STILL AN ISSUE IN THE LOW TO
MID-LEVELS, AS EVIDENCED BY A CLEAR SLOT THAT IS WRAPPING ALL THE
WAY AROUND THE SYSTEM AND IMPINGING ON THE CORE FROM THE WEST.
INITIAL WIND RADII BASIS: SAR AND SCATTEROMETER DATA
CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 105 KTS AT 041723Z
   CIMSS ADT: 100 KTS AT 041810Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: LOW TO MID-LEVEL DRY AIR INTRUSION
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 TRACKING GENERALLY
NORTHWARD IN THE NEAR-TERM, BUT IS EXPECTED TO TURN OVER TOWARDS
THE NORTHEAST BY TAU 12 AS IT BEGINS TO ROUND THE RIDGE AXIS AND
ACCELERATES NORTHEASTWARD TOWARDS THE KOREAN PENINSULA. LANDFALL IS
EXPECTED ALONG THE SOUTHERN COAST OF KOREA NEAR BUSAN AROUND TAU
30. FROM AN INTENSITY PERSPECTIVE, THE SYSTEM STILL HAS A SHORT
WINDOW IN WHICH CONDITIONS WILL REMAIN FAVORABLE FOR
INTENSIFICATION. WITH THE SECONDARY EYEWALL HAVING ERODED, THERE IS
MUCH LESS PROBABILITY OF AN EYEWALL REPLACEMENT CYCLE AT THIS
POINT, WITH THE M-PERC PROBABILITIES TAKING A NOSEDIVE OVERNIGHT,
NOW DOWN TO LESS THAN 10 PERCENT. HAVING ESTABLISHED A GOOD
POLEWARD OUTFLOW CHANNEL, WHICH WILL ONLY IMPROVE OVER TIME, AND A
BUFFER OF ENHANCED OUTFLOW TO THE WEST BLOCKING ANY IMPINGING
WESTERLY FLOW FROM THAT SECTOR, SHEAR LOOKS TO REMAIN LOW FOR A
LEAST THE NEXT 12 HOURS. THE MAIN IMPEDIMENT WILL BE THE STUBBORN
LOW TO MID-LEVEL DRY AIR WHICH CONTINUES TO BE PULLED OFF THE
CHINESE MAINLAND AND INTO THE CORE OF THE SYSTEM. IF IT CAN FIGHT
OFF THE DRY AIR, TY 12W STILL HAS A SHORT WINDOW OF FAVORABLE
CONDITIONS TO INTENSIFY A BIT MORE, LIKELY PEAKING WITHIN THE NEXT
6 TO 12 HOURS. BUT AFTER TAU 12 TY 12W WILL BEGIN TO INTERACT WITH
AN APPROACHING MID-LATITUDE TROUGH WITH STRONG DYNAMIC SUPPORT
INCLUDING A ROBUST JET MAX AND NEGATIVELY TILTED 500MB TROUGH. BY
TAU 24, JUST EAST OF CHEJU DO, THE SYSTEM WILL MOVE OVER
SIGNIFICANTLY COOLER WATERS, BE ASSAULTED BY VERY DRY AIR IN THE
MID-LEVELS AND STARTS TO BE DECAPITATED BY VERY STRONG WESTERLY
SHEAR. THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU
24 OR SHORTLY THEREAFTER AS IT BEGINS TO COUPLE WITH THE SOUTHERN
END OF THE UPPER-LEVEL TROUGH. WHILE THE SYSTEM WILL RAPIDLY LOSE
ITS TROPICAL CHARACTERISTICS AND BE SHEARED APART AS IT MOVES OVER
THE SOUTHERN KOREAN PENINSULA, THE STRONG BAROCLINC FORCING
ASSOCIATED WITH THE MID-LATITUDE SYSTEM WILL RESULT HIGHER
INTENSITIES THAN OTHERWISE EXPECTED FROM A WEAKENING TROPICAL
CYCLONE. BETWEEN TAUS 36 AND 48, THE SYSTEM WILL LOSE ALL OF ITS
REMAINING TROPICAL CHARACTERISTICS AND BECOME A TYPHOON-STRENGTH
EXTRA-TROPICAL LOW IN THE NORTHERN SEA OF JAPAN.
MODEL DISCUSSION: TRACK GUIDANCE, WITH THE CONTINUED EXCEPTION OF
THE JGSM, REMAINS IN VERY TIGHT AGREEMENT THROUGH THE FORECAST
PERIOD, WITH JUST A 50-NM SPREAD AS THE SYSTEM CROSSES THE COAST OF
SOUTH KOREA. THE ENVELOPE EXPANDS BOTH ACROSS AND ALONG-TRACK AS
THE SYSTEM GOES EXTRA-TROPICAL, BUT STILL REMAINS IN GOOD
AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.
INTENSITY GUIDANCE HAS COME INTO BETTER AGREEMENT SINCE THE
PREVIOUS RUN, THOUGH THERE REMAIN TWO DISTINCT GROUPINGS THROUGH
ABOUT TAU 36. THE HWRF AND DECAY-SHIPS (GFS AND NVGM) MODELS CONCUR
IN A STEADY-STATE INTENSITY TO TAU 12, FOLLOWED BY SHARP AND STEADY
WEAKENING THROUGH THE REMAINDER OF THE FORECAST.  MEANWHILE THE
COAMPS-TC AND GFS SHOW SHARP WEAKENING FROM TAU 00. AS DISCUSSED
ABOVE, THE SYSTEM WILL LIKELY PEAK IN THE NEXT 6 TO 12 HOURS BUT
THEN BEGIN TO WEAKEN AGAIN BY TAU 12 RESULTING IN A STEADY-STATE
INTENSITY FORECAST AT TAU 12. THE JTWC FORECAST TRACKS THE HWRF,
SHIPS AND CONSENUS GUIDANCE CLOSELY THROUGH THE FORECAST PERIOD,
AND LIES ALONG THE HIGHER EDGE OF THE GUIDANCE ENVELOPE, WITH
MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: ---
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: ---
//
NNNN
NNNN