Tropical Storm HINNAMNOR Advisory 9月3日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (HINNAMNOR) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 22.4N 124.7E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 299 NM SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE
CIRCULATION, WITH A RAGGED CORE OF DISORGANIZED CONVECTION. THE
CONVECTIVE ENVELOPE IS DISPLACED PRIMARILY TO THE SOUTH AND EAST OF
THE ASSESSED LOW LEVEL CENTER (LLC) DUE TO PERSISTENT, THOUGH
WEAKENING, NORTHERLY SHEAR. WATER VAPOR IMAGERY SUGGESTS A SMALL
ANTICYCLONE OVER TOP OF THE SYSTEM WHICH IS EXPANDING RADIALLY, BUT
PARTICULARLY POLEWARD AND EASTWARD, COMPLIMENTING THE ALREADY GOOD
EQUATORWARD OUTFLOW. ANIMATED RADAR IMAGERY REVEALS A WELL DEFINED
40NM WIDE EYE FEATURE AND LATER EIR AROUND THE 2000Z HOUR SUGGESTS
DEVELOPMENT OF A NASCENT INFRARED EYE. GALE-FORCE WIND RADII HAVE
BEEN ADJUSTED, EXPANDING ROUGHLY 100NM FURTHER IN THE SOUTHEAST
SECTOR, BUT CONTRACTING IN THE NORTHERN SECTORS, AS SURFACE WINDS
REMAIN SUB-GALE FORCE AT BOTH MIYAKOJIMA AND ISIGAKIJIMA. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
RADAR DATA. THE INITIAL INTENSITY OF 75 KNOTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON AGENCY DVORAK CURRENT INTENSITY
ESTIMATES, THOUGH DATA-T NUMBERS HAVE LOWERED DOWN TO THE T4.0
RANGE. ADT AND AIDT ESTIMATES HAVE REMAINED FAIRLY STEADY OVER THE
PAST SIX HOURS AT 74 AND 75 KNOTS RESPECTIVELY.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.0 - 90 KTS
   RJTD: T5.0 - 90 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 82 KTS AT 021711Z
   CIMSS ADT: 74 KTS AT 021740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: UPWELLING OF COOLER WATER
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: REGIONAL UPPER-AIR SOUNDINGS AND ANALYSIS
SUPPORTS THE MODEL DATA SUGGESTING THE WEAKENING OF THE STR OVER
CHINA, AND THE STRENGTHENING OF THE STR TO THE EAST, WITH THE
STEERING GRADIENT TIGHTENING UP ON THE EASTERN SIDE OF TY 12W. THE
RESULT IS THAT THE STR TO THE EAST HAS NOW ASSUMED THE PRIMARY
STEERING ROLE, AND IS STARTING TO KICK TY 12W OUT OFF TO THE NORTH,
THOUGH SLOWLY FOR THE TIME BEING. THE SYSTEM IS EXPECTED TO TRACK
RATHER SLOWLY NORTHWARD OVER THE NEXT 24 HOURS AS IT PASSES JUST
EAST OF ISHIKAGIJIMA, THEN WILL ACCELERATE NORTHWARD INTO THE EAST
CHINA SEA AS THE RIDGE CONTINUES TO BUILD TO THE EAST. A SHARP TURN
TO THE NORTHEAST IS FORECAST TO START BY TAU 48 AS THE RIDGE GETS
PUSHED TO THE NORTHEAST BY THE APPROACH OF A MAJOR MID-LATITUDE
TROUGH FROM THE WEST. THE SYSTEM WILL PASS OVER THE SOUTHERN
PORTION OF SOUTH KOREA AND MOVE RAPIDLY INTO THE SEA OF JAPAN BY
TAU 96. THE WHILE THE UPPER-LEVEL ENVIRONMENT IS STEADILY
IMPROVING, THE SLOW FORWARD MOTION OF TY 12W MEANS THAT IT WILL
REMAIN OVER RELATIVELY COOL WATERS, BROUGHT ON BY THE RECENT
UPWELLING EVENT, FOR ABOUT 12 HOURS OR SO, INHIBITING SIGNIFICANT
INTENSIFICATION IN THE NEAR-TERM. ONCE IT MOVES TO THE NORTH OF THE
RYUKUS HOWEVER, MORE RAPID INTENSIFICATION IS EXPECTED AS THE
SYSTEM WILL TAP INTO A POLEWARD OUTFLOW CHANNEL AHEAD OF THE
APPROACHING MID-LATITUDE TROUGH, REACHING A PEAK OF 105 KNOTS BY
TAU 48. AFTER THE SYSTEM TURNS NORTHEASTWARD TOWARDS KOREA, IT WILL
BEGIN TO FEEL THE EFFECTS OF DECREASING SSTS AND INCREASING SHEAR,
WHICH WILL BEGIN TO WEAKEN THE SYSTEM, DOWN TO 85 KNOTS BY TAU 72.
AT THIS POINT THE SYSTEM WILL BEGIN TO INTERACT WITH THE
MID-LATITUDE WESTERLY FLOW AND BEGIN EXTRA-TROPICAL TRANSITION
(ETT), WITH THE SYSTEM TRANSITIONING TO A STORM-FORCE
EXTRA-TROPICAL LOW IN THE SEA OF JAPAN NO LATER THAN TAU 96.
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS
IN GOOD AGREEMENT THROUGH THE DURATION OF THE FORECAST, WITH 100NM
TO 150NM SPREAD FROM TAU 48 TO 72. ALONG-TRACK SPREAD INCREASES
SIGNIFICANTLY AFTER TAU 72 AS THE SYSTEM UNDERGOES ETT. ENSEMBLE
GUIDANCE DEPICTS A BIT MORE UNCERTAINTY WITH THIS RUN, WITH THE
ECENS ENVELOPE NOW EXTENDING FROM COASTAL CHINA TO ABOUT 126E, MUCH
LARGER THAN WITH PREVIOUS RUNS. THE GEFS ENVELOPE HAS ALSO
EXPANDED, BUT REMAINS MORE TIGHTLY CONFINED THAN ECENS. OVERALL
CONFIDENCE IS HIGH UP THROUGH TAU 48 BUT THEN DECREASES FAIRLY
QUICKLY TO MEDIUM IN THE LONGER-TERM. COAMPS-TC ENSEMBLE INTENSITY
GUIDANCE SUGGESTS A HIGH LIKELIHOOD OF MODERATE INTENSIFICATION,
WITH ABOUT THIRTY PERCENT CHANCE OF RAPID INTENSIFICATION AROUND
TAU 36 TO TAU 48. THE REMAINDER OF THE DETERMINISTIC GUIDANCE IS
CONSTRAINED BETWEEN 90 TO 120 KNOTS, WITH COAMPS-TC ON THE HIGH END
AND THE CONSENSUS MEAN ON THE LOW SIDE, THOUGH THIS IS BEING PULLED
LOW DUE TO THE UNREALISTIC DECAY-SHIPS GUIDANCE WHICH SHOWS NO
FURTHER INTENSIFICATION IN THE FORECAST PERIOD. THE JTWC FORECAST
LIES CLOSE TO THE HWRF SOLUTION, ABOVE THE CONSENSUS, WITH MEDIUM
CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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