Tropical Storm FENGSHEN Advisory 11月14日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W (FENGSHEN)
WARNING NR 014//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 26W (FENGSHEN), LOCATED APPROXIMATELY 40
NM WEST OF PAGAN, HAS TRACKED WEST-NORTHWESTWARD AT 15 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
DEPICTS DEEP CONVECTIVE BANDING WRAPPING INTO A WELL-DEFINED LOW-
LEVEL CIRCULATION CENTER. A 141556Z AMSR-2 36GHZ COMPOSITE IMAGE
DEPICTS A MICROWAVE EYE FEATURE, WHICH, ALONG WITH WRAPPING INTO THE
CENTER, SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. THE
INITIAL INTENSITY IS ASSESSED AT 60 KNOTS  BASED ON THE IMPROVED
CONVECTIVE STRUCTURE AND A 141602Z SATCON OF 70 KTS. DVORAK CURRENT
INTENSITY ESTIMATES ARE LOWER, AT T3.5 (55 KNOTS). TS 26W IS LOCATED
IN AN AREA OF LOW TO MODERATE (5-10 KNOTS) VERTICAL WIND SHEAR, WARM
SEA SURFACE TEMPERATURES (28-29C) AND MODERATE WESTWARD AND
EQUATORWARD DIFFLUENCE ALOFT. TS 26W IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL STEERING RIDGE SITUATED TO
THE NORTH.
3. FORECAST REASONING.
   A.  THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 26W IS FORECAST TO GRADUALLY RECURVE AROUND THE WESTERN
PERIPHERY OF THE BROAD STR AFTER TAU 24. LOW VERTICAL WIND SHEAR,
PASSAGE OVER WARM WATER AND IMPROVING POLEWARD OUTFLOW AS IT TAPS
INTO A PASSING MIDLATITUDE TROUGH TO THE NORTH WILL LIKELY FUEL
STEADY INTENSIFICATION THROUGH TAU 36 WITH A PEAK INTENSITY OF 85
KNOTS EXPECTED AT TAU 36. AFTER TAU 36, A WEAKENING TREND WILL BEGIN
AS THE SYSTEM SLIDES UNDER UPPER-LEVEL WESTERLY WINDS AND ENCOUNTERS
INCREASING VERTICAL WIND SHEAR. NUMERICAL MODEL GUIDANCE IS IN GOOD
AGREEMENT WITH THIS OVERALL SCENARIO THROUGH TAU 48 IN CROSS-TRACK
SPREAD, BUT THERE ARE STILL SIGNIFICANT ALONG-TRACK SPEED DIFFERENCES
BETWEEN MODEL SOLUTIONS, LENDING POOR CONFIDENCE TO THE INITIAL
PORTION OF THE TRACK FORECAST.
   C. IN THE EXTENDED FORECAST PERIOD, TS 26W IS EXPECTED TO WEAKEN
QUICKLY UNDER STRONG (40 TO 50 KNOTS) WESTERLY VERTICAL WIND SHEAR.
THE PRIMARY STEERING INFLUENCE WILL SHIFT TO A LOW-LEVEL HIGH THAT
IS FORECAST TO BUILD TO THE NORTH AFTER TAU 48, STEERING TS 26W BACK
TO THE WEST. NUMERICAL MODELS AGREE WITH THIS OVERALL FORECAST
SCENARIO, BUT VARY IN THEIR DEPICTIONS OF THE RATE OF WEAKENING AND
EXACT TRACK DURING THE EXTENDED PERIOD. ECMWF HAS ACCELERATED ITS
ALONG-TRACK MOTION IN THE LONG-TERM FORECAST SIGNIFICANTLY AND NOW
TURNS SOUTH MUCH LATER THAN THE OTHER MODELS DUE TO BUILDING THE LOW
LEVEL RIDGING IN LATER. NAVGEM REFLECTS THE QUICKEST TURN TO THE
SOUTH. ECMWF, NAVGEM, AND GFS ARE TO THE INSIDE OF THE MULTI-MODEL
CONSENSUS. UKMET AND AFUM ARE SIGNIFICANTLY SLOWER IN ALONG-TRACK
MOTION AND ARE THE OUTSIDE OUTLIERS. THE JTWC FORECAST TRACK HAS BEEN
SHIFTED SIGNIFICANTLY FURTHER EAST IN LATER TAUS TO REFLECT THE
ACCELERATED ALONG-TRACK MOTION IN MOST MODELS. THERE IS LOW
CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK DUE TO THE
COMPLEX STEERING ENVIRONMENT, DRAMATIC ALONG-TRACK SPEED DIFFERENCES
BETWEEN THE PREVIOUS AND CURRENT MODEL RUNS, AND DIFFERENCES IN
TIMING OF THE SOUTHWARD TURN.//
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