Tropical Storm TRAMI Advisory 9月25日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 28W (TRAMI) WARNING NR
17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 28W (TRAMI), LOCATED APPROXIMATELY 420 NM
SOUTH OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT
06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED A HIGHLY SYMMETRIC
EYEWALL SURROUNDING A 36 NM EYE, WHICH SUPPORTS THE INITIAL POSITION
WITH HIGH CONFIDENCE. THE EIR LOOP ALSO SHOWS THE FEEDER BANDS HAVE
BEEN STRIPPED SHORT AND TUCKED INTO A MORE COMPACT AND CONSOLIDATED
SYSTEM. THE INITIAL INTENSITY OF 140 KNOTS IS BASED ON EQUIVALENT AND
NEAR-CONCENTRIC DVORAK FIXES OF T7.0/140 KTS FROM PGTW AND RJTD. STY
28W IS IN AN AREA OF LOW VERTICAL WIND SHEAR AND ROBUST RADIAL
OUTFLOW WITH A STRONG POLEWARD CHANNEL INTO A DEEP UPPER-LEVEL
SHORTWAVE TROUGH OVER THE EAST CHINA SEA. ADDITIONALLY, SEA SURFACE
TEMPERATURES IN THE PHILIPPINE SEA ARE HIGHLY CONDUCIVE AT 30
CELSIUS. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF
A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THE EXTENDED PORTION OF THE TRACK FORECAST SHOWS A SHARPER
RECURVE NORTHEASTWARD, OTHERWISE, THERE IS NO SIGNIFICANT CHANGE TO
THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING
MESSAGE.
   B. STY 28W IS FORECAST TO TRACK SLOWLY NORTHWESTWARD THEN
NORTHWARD UNDER THE STEERING INFLUENCE OF THE STR. THE AFOREMENTIONED
MIDLATITUDE SHORTWAVE TROUGH WILL DEEPEN AND DIG INTO THE STR,
CAUSING THE POLEWARD TURN AND THE SIGNIFICANT DECREASE IN THE TRACK
SPEED. AFTER TAU 36, THE STR IS EXPECTED TO SLOWLY REBUILD AND DRIVE
THE SYSTEM BACK TO A NORTHWESTWARD COURSE. THE FAVORABLE ENVIRONMENT
WILL PREVAIL IN THE NEAR-TERM, LEADING TO A PEAK INTENSITY OF 145
KNOTS BY TAU 12. AFTERWARD, DECREASING OUTFLOW WILL PRIMARILY CAUSE A
GRADUAL WEAKENING, DOWN TO 115 KNOTS BY TAU 72. NUMERICAL MODEL
GUIDANCE IS BIFURCATED WITH THE MAJORITY INDICATING THE POLEWARD TURN
AND JGSM AND NVGM OFFERING A STRAIGHT WEST-NORTHWESTWARD SOLUTION.
ADDITIONALLY, THERE ARE SIGNIFICANT DIFFERENCES IN TRACK SPEEDS AND A
NOTABLE SPREAD IN THE POLEWARD TRACK AMONG THE MAJORITY MEMBERS. IN
VIEW OF THESE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC
TRACK FORECAST THAT IS LAID TO THE RIGHT OF CONSENSUS TO OFFSET THE
UNLIKELY JGSM/NVGM SOLUTION.
   C. AFTER TAU 72, STY TRAMI WILL CONTINUE ON A NORTHWESTWARD TRACK
UNDER A REBUILT STR, AND AFTER TAU 96, WILL CREST THE STR RIDGE AND
RECURVE NORTHEASTWARD. THE WEAKENING TREND WILL EXTEND UP TO TAU 96
WHEN THE SYSTEM WILL BE REDUCED TO 105 KNOTS; HOWEVER, AFTER TAU 96,
A RESURGENCE IN THE POLEWARD OUTFLOW ASSOCIATED WITH THE PREVAILING
WESTERLIES WILL FUEL A SECONDARY INTENSIFICATION PHASE, REACHING 115
KNOTS BY TAU 120. NUMERICAL MODEL GUIDANCE SPREADS OUT EVEN MORE IN
THE EXTENDED TAUS, LEADING TO LOW CONFIDENCE IN THE LATTER PORTION OF
THE JTWC TRACK FORECAST, AS WELL.//
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