Tropical Storm SURIGAE Advisory 4月20日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 02W (SURIGAE) WARNING NR 026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 02W (SURIGAE), LOCATED APPROXIMATELY 284 NM EAST OF
MANILA, PHILIPPINES, HAS TRACKED NORTHWARD AT 03 KTS OVER THE PAST
SIX HOURS. SURIGAE CONTINUES TO MAINTAIN A LARGE, CLEARLY-DEFINED
EYE OF 30 NM DIAMETER IN ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY. SOME EROSION OF DEEP CONVECTION IN THE INNER CORE HAS BEEN
NOTED OVER THE PAST SIX HOURS, PERIODICALLY CAUSING THE APPEARANCE
OF A DRY MOAT BETWEEN THE 30 NM EYEWALL AND A LARGER, OUTER RING OF
DEEP CONVECTION APPROXIMATELY 60 NM IN DIAMETER. THIS OUTER RING
APPEARS TO BE THE DOMINANT FEATURE IN A RECENT 191951Z SSMIS
MICROWAVE IMAGE. THE CURRENT INTENSITY IS LOWERED SLIGHTLY TO 115
KTS, BASED ON THE PGTW FIX OF T6.0/6.5 AND ADT ESTIMATES OF T6.0.
COUPLED HWRF/HYCOM OCEAN ANALYSIS SUGGESTS THAT SLOW MOVEMENT OF THE
LARGE TYPHOON IS INDUCING COOLING OF THE UNDERLYING WATER, POSSIBLY
CONTRIBUTING TO THE CURRENT RAGGEDNESS OF INNER CORE CONVECTION AND
GRADUAL DECREASE IN INTENSITY. SURIGAE REMAINS SITUATED IN AN
OTHERWISE FAVORABLE ENVIRONMENT, LOCATED JUST SOUTH OF THE AXIS OF A
200MB RIDGE, WITH LIGHT VERTICAL WIND SHEAR OF 5-10 KTS. WATER VAPOR
SATELLITE IMAGERY DEPICTS A COOL, DRY MID-LATITUDE AIR MASS GETTING
PULLED SOUTHWARD OVER LUZON ON THE WEST SIDE OF THE TYPHOON, BUT
THERE IS NO EVIDENCE THAT THIS AIR MASS IS GETTING ENTRAINED INTO
THE STORM CORE AT THIS TIME.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY
SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. SURIGAE IS EXPECTED TO CONTINUE MOVING SLOWLY NORTH-
NORTHWESTWARD DURING THE NEXT 48 HOURS AS A WEAK UPPER-LEVEL RIDGE
TO ITS EAST CONTINUES TO INDUCE A WEAK SOUTHERLY STEERING FLOW. THIS
STEERING FLOW MAY STRENGTHEN SLIGHTLY AS A LOW-AMPLITUDE UPPER-LEVEL
RIDGE WITHIN THE SUBTROPICAL JET (STJ) TRANSLATES EASTWARD FROM THE
VICINITY OF TAIWAN TO THE NORTH OF THE TYPHOON. THUS, FORWARD SPEED
IS EXPECTED TO INCREASE SLIGHTLY FROM THE CURRENT SLOTHFUL PACE
WITHIN THE NEXT 12-24 HOURS. AFTER 48 HOURS, SURIGAE WILL ROUND THE
NORTHWESTERN PERIPHERY OF THE RIDGE TO ITS EAST, AND A SHORTWAVE
TROUGH WILL APPROACH FROM THE NORTHWEST OVER EASTERN CHINA. THE
RESULTING INCREASE IN MID-LEVEL WESTERLY FLOW WILL ACCELERATE AND
TURN THE CYCLONE NORTHEASTWARD BY 72 HOURS. THE TRACK FORECAST
THROUGH 72 HOURS IS NUDGED SLIGHTLY EASTWARD COMPARED TO THE
PREVIOUS ONE TO ACCOUNT FOR THE MORE NORTHWARD TREND IN SHORT-TERM
MOTION, BUT REMAINS OF HIGH CONFIDENCE. THE INTENSITY FORECAST
THROUGH 48 HOURS IS EXPECTED TO LARGELY BE A FUNCTION OF DYNAMIC
OCEAN COOLING OCCURRING BENEATH SURIGAE, WHICH SHOULD CONTINUE AS
THE TYPHOON MOVES SLOWLY. GRADUAL WEAKENING TO 100 KTS IS FORECAST
BY 48 HOURS. THEREAFTER, VERTICAL WIND SHEAR IS EXPECTED TO INCREASE
AS THE TYPHOON TURNS NORTHEASTWARD, IN RESPONSE TO INCREASING
WESTERLY MID-LEVEL FLOW AND A COOLING OF BACKGROUND SEA SURFACE
TEMPERATURES FROM 28C TO AROUND 26C. QUICKER WEAKENING IS LIKELY
AFTER 48 HOURS AS THIS OCCURS.
   C. DURING THE 96-120 HOUR PERIOD, SURIGAE IS EXPECTED TO INTERACT
WITH A STRONG LOW-LEVEL BAROCLINIC ZONE SOUTH OF JAPAN, PRESSING
SOUTHWARD ACROSS THE RYUKYU ISLANDS. THIS SHOULD CATALYZE THE
PROCESS OF EXTRATROPICAL TRANSITION. WEAKENING BELOW TYPHOON
INTENSITY IS FORECAST THROUGH 120 HOURS, AS THE INTERACTION WITH THE
STJ IS NOT PARTICULARLY FAVORABLE FOR BAROCLINIC-INDUCED
REINTENSIFICATION AS A POSITIVELY-TILTED SHORTWAVE TROUGH DIGS
THROUGH THE EAST CHINA SEA DUE WEST OF THE CYCLONE. THE TRACK
FORECAST REMAINS SIMILAR TO THE PREVIOUS ONE, NUDGED JUST SLIGHTLY
NORTH THROUGH 120 HOURS TOWARD THE NEW MULTI-MODEL CONSENSUS.
CONFIDENCE IS MODERATE DUE TO SOME UNCERTAINTY IN FORWARD SPEED
DURING EXTRATROPICAL TRANSITION. //
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