Tropical Storm LAN Advisory 10月20日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (LAN) WARNING NR 18//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 25W (LAN), LOCATED APPROXIMATELY 523 NM SOUTH-SOUTHEAST
OF KADENA AB, HAS TRACKED NORTHWARD AT 10 KNOTS OVER THE PAST SIX
HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS DEEP
BANDING WRAPPING INTO A LARGE, WELL DEFINED LOW LEVEL CIRCULATION
CENTER (LLCC). THE SYSTEM REMAINS VERY BROAD, COVERING OVER 900 NM.
A 191754Z 85 GHZ SSMI IMAGE SHOWS DEEP CONVECTIVE BANDING WRAPPING
INTO A WELL DEFINED MICROWAVE EYE FEATURE. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE PREVIOUSLY MENTIONED
MICROWAVE EYE FEATURE. THE INITIAL INTENSITY OF 75 KNOTS IS BASED
ON DVORAK INTENSITY ASSESSMENTS OF T4.5 (77 KNOTS) FROM BOTH PGTW
AND RJTD. ENVIRONMENTAL ANALYSIS INDICATES THAT THE SYSTEM IS IN AN
AREA OF LOW (5-15 KNOT) VERTICAL WIND SHEAR (VWS) THAT IS BEING
OFFSET BY ROBUST RADIAL OUTFLOW. TYPHOON LAN IS TRACKING THOUGH AN
AREA OF VERY WARM (30 TO 31 CELSIUS) SEA SURFACE TEMPERATURES
(SSTS) AND HIGH OCEAN HEAT CONTENT. TY 25W IS TRACKING ALONG THE
WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) LOCATED
TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 25W IS FORECAST TO TRACK NORTHWARD OVER THE NEXT 12-24
HOURS UNDER THE INFLUENCE OF THE STR. AFTER CROSSING THE RIDGE AXIS
AROUND TAU 24, THE SYSTEM WILL BEGIN TO RECURVE BACK TO THE
NORTHEAST. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST AND
POLEWARD OUTFLOW WILL BE ENHANCED AS THE SYSTEM APPROACHES THE MID-
LATITUDE WESTERLIES. INTERACTION WITH THE WESTERLIES WILL ALLOW FOR
A BRIEF PERIOD OF RAPID INTENSIFICATION, REACHING A PEAK INTENSITY
OF 105 KNOTS AROUND TAU 36. AFTER TAU 48, THE SYSTEM WILL BEGIN TO
GRADUALLY WEAKEN AS VERTICAL WIND SHEAR INCREASES AND THE SYSTEM
BEGINS TO INTERACT WITH AN APPROACHING MID-LATITUDE TROUGH. BY TAU
72, TY 25W WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT). DYNAMIC
MODEL GUIDANCE IS IN STRONG AGREEMENT, LENDING HIGH CONFIDENCE IN
THIS PORTION OF THE JTWC TRACK FORECAST.
   C. AFTER TAU 72, TY LAN WILL ACCELERATE NORTHEASTWARD AS IT
BECOMES EMBEDDED IN THE BAROCLINIC ZONE. AROUND TAU 60, THE SYSTEM
IS FORECAST TO MAKE A BRIEF LANDFALL NEAR TOKYO. AFTER EXITING BACK
INTO THE PACIFIC OCEAN, THE SYSTEM IS FORECAST TO CONTINUE TO TRACK
TO THE NORTHEAST AND COMPLETE EXTRA-TROPICAL TRANSITION BY TAU 96,
BECOMING A HURRICANE-FORCE COLD CORE LOW WITH AN EXPANSIVE WIND
FIELD. INCREASING VWS AND THE SYSTEM TRACKING THROUGH AN AREA OF
COOLER (<26 CELSIUS) SEA SURFACE TEMPERATURES WILL CONTINUE TO
WEAKEN THE SYSTEM FOR THE DURATION OF THE FORECAST PERIOD. DYNAMIC
MODEL GUIDANCE IS IN TIGHT AGREEMENT DIRECTION-WISE, HOWEVER,
VARIATIONS IN THE TRACK SPEED AFTER TAU 72 LEAD TO A SIGNIFICANT
SPREAD BY TAU 120. DUE TO THE UNCERTAINTY IN STORM SPEED AND SPREAD
IN THE MODEL GUIDANCE, THERE IS LOW CONFIDENCE IN THIS PORTION OF
THE JTWC TRACK FORECAST.//
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