Tropical Storm TRAMI Advisory 9月27日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (TRAMI) WARNING NR 25//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 28W (TRAMI), LOCATED APPROXIMATELY 315 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWARD AT 01 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS
TY 28W MAINTAINS A WIDE EYE, WITH RESURGENT CONVECTION IN THE
EYEWALL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED
ON THE WIDE EYE IN THE EIR LOOP. THE INITIAL INTENSITY IS
MAINTAINED AT 90 KNOTS, BETWEEN MULTIAGENCY DVORAK CURRENT
INTENSITY (CI) ESTIMATES RANGING FROM T4.5 (77 KTS) TO T5.5 (102
KTS), AND IN AGREEMENT WITH A 261705Z SATCON ESTIMATE OF 91 KNOTS.
ENVIRONMENTAL ANALYSIS SHOWS TY 28W IS EXPERIENCING FAVORABLE
VERTICAL WIND SHEAR (5 TO 10 KNOTS) ALONG WITH GOOD RADIAL OUTFLOW,
WHICH IS BEING ENHANCED BY A PASSING MIDLATITUDE TROUGH TO THE
NORTH. SEA SURFACE TEMPERATURES REMAIN FAVORABLE NEAR 28 DEGREES
CELSIUS, ALTHOUGH THE SLOW MOTION OF TY 28W IS CAUSING UPWELLING
AND REDUCING THE AVAILABLE OCEAN HEAT CONTENT (OHC) FOR THE SYSTEM,
CONTRIBUTING TO ITS STRUGGLE TO MAINTAIN DEEP CONVECTION. TY 28W IS
ALMOST QUASI-STATIONARY IN A WEAK STEERING ENVIRONMENT WHILE
BETWEEN A SUBTROPICAL RIDGE (STR) LOCATED TO THE WEST AND A SECOND
STR LOCATED TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 28W IS FORECAST TO TRACK SLOWLY NORTH TO NORTHWESTWARD IN
THE AMBIGUOUS STEERING ENVIRONMENT WHILE MAINTAINING ITS INTENSITY,
CAUGHT IN A BALANCE BETWEEN FAVORABLE OUTFLOW AND LOW VWS, AND THE
UNFAVORABLE LOWER OHC. AFTER TAU 12, THE STR TO THE EAST WILL
BUILD, BECOME THE DOMINANT STEERING FEATURE, AND ALLOW TY 28W TO
INCREASE FORWARD MOTION AND TRACK NORTHWESTWARD THROUGH TAU 48. BY
TAU 36, TY 28W WILL ENCOUNTER AN AREA OF WARM (28-30 C) SSTS THAT
IT HAS NOT ALREADY CHURNED UP, WHICH WILL ALLOW FOR A PERIOD OF RE-
INTENSIFICATION, REACHING 110 KTS BY TAU 72. MODELS ARE IN
AGREEMENT THAT TY 28W WILL TRACK NORTHWESTWARD, WITH NAVGEM A
NOTABLE OUTLIER TO THE WEST DUE TO IT BUILDING IN A MORE ROBUST STR
TO THE EAST. THE JTWC FORECAST TRACK IS PLACED JUST TO THE WEST OF
THE MULTI-MODEL CONSENSUS, CLOSER TO THE ECMWF SOLUTION, PASSING
CLOSE TO OKINAWA AROUND TAU 60. THE LAST SEVERAL MODEL RUNS SHOW
THE MULTI-MODEL CONSENSUS TRENDING CLOSER TO OKINAWA, FAVORING A
TIGHTER RECURVE SCENARIO. DUE TO THE 360 NM MODEL SPREAD AT TAU 72,
THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, TY 28W IS FORECAST TO ACCELERATE NORTHEASTWARD
TOWARD MAINLAND JAPAN AS IT ROUNDS THE STR AXIS AND IS PULLED BY A
PASSING MIDLATITUDE TROUGH. INCREASED VERTICAL WIND SHEAR, COOLER
SEA SURFACE TEMPERATURES, AND EVENTUAL LAND INTERACTION WILL WEAKEN
THE SYSTEM AS IT TRACKS NORTHEASTWARD. TY 28W WILL BE EMBEDDED IN
THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY
TAU 96, AND WILL COMPLETE ETT BY TAU 120. THE JTWC FORECAST TRACK
IS PLACED NEAR THE MULTI-MODEL CONSENSUS. MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT TY 28W WILL TRACK NORTHEASTWARD, BUT MODELS DIFFER
ON THE TRACK SPEED. THEREFORE, THERE IS LOW CONFIDENCE IN THIS
PORTION OF THE JTWC FORECAST TRACK.//
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