Tropical Storm SURIGAE Advisory 4月24日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUBTROPICAL STORM 02W (SURIGAE)
WARNING NR 042//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUBTROPICAL STORM (SS) 02W (SURIGAE), LOCATED APPROXIMATELY 247
NM SOUTHEAST OF KADENA AB, HAS TRACKED EASTWARD AT 06 KNOTS OVER
THE PAST SIX HOURS. INFRARED SATELLITE IMAGERY SHOWS THAT DEEP
CONVECTION HAS VANISHED OVER THE CIRCULATION AS IT PASSES OVER A
COLD OCEANIC EDDY WITH COLD SEA SURFACE TEMPERATURES OF 23-24
DEGREES CELSIUS. WATER VAPOR SATELLITE IMAGERY INDICATES THAT AN
UPPER-LEVEL SHORTWAVE HAS PASSED OVER THE RYUKYU ISLANDS AND IS NOW
SUPERIMPOSING WITH SURIGAE'S CIRCULATION. THIS IS BRINGING ABOUT A
REDUCTION IN BAROCLINIC FORCING THAT IS ALLOWING THE CYCLONE TO
CONTINUE DECAYING. A 231257Z ASCAT-B PASS INDICATED WINDS IN EXCESS
OF 65 KTS IN THE NORTHWEST QUADRANT OF THE STILL WELL-DEFINED
CIRCULATION. THE WIND FIELD CONSISTS OF A SYMMETRIC CORE WITH A
GROWING ASYMMETRIC EXTENSION TO THE NORTHEAST IN RESPONSE TO WARM
ADVECTION AND BAROCLINIC INTERACTION. THE CURRENT INTENSITY IS SET
AT 60 KTS, ASSUMING THE WEAKENING TREND HAS CONTINUED SINCE THAT
TIME. THE ENVIRONMENT REMAINS HOSTILE WITH VERTICAL WIND SHEAR OF 40-
50 KTS, ABUNDANT DRY AIR IN THE SOUTHERN SEMICIRCLE, AND THE
AFOREMENTIONED COLD SEA SURFACE TEMPERATURES.
3. FORECAST REASONING.
   A. 02W HAS NOW BEEN CLASSIFIED AS A SUBTROPICAL CYCLONE BASED ON
ITS LACK OF DEEP CONVECTION, ENTANGLEMENT WITH A COLD-CORE UPPER-
LEVEL TROUGH, AND INCREASINGLY ASYMMETRIC STRUCTURE. EXTRATROPICAL
TRANSITION IS STILL EXPECTED BY TAU 48. THERE IS NO SIGNIFICANT
CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. SS 02W (SURIGAE) WILL CONTINUE STEADILY WEAKENING OVER THE
NEXT 24 HOURS AS IT LOSES BAROCLINIC SUPPORT FROM THE UPPER-LEVEL
SHORTWAVE CURRENTLY SUPERIMPOSING WITH THE CIRCULATION, BUT IS
EXPECTED TO RETAIN GALE-FORCE WINDS. AROUND 36 HOURS, A SECOND
SHORTWAVE TROUGH CURRENTLY ENTERING THE YELLOW SEA WILL APPROACH
SURIGAE, REINTRODUCING BAROCLINIC FORCING. THIS MAY STRENGTHEN AND
INTENSIFY THE WIND FIELD SLIGHTLY BY 48 HOURS, AND WILL ALSO BRING
ABOUT THE CONCLUSION OF EXTRATROPICAL TRANSITION. THE FORECAST TRACK
IS SIMILAR TO THE PREVIOUS ONE, PASSING NEAR IWO TO IN AROUND 48
HOURS. THE MODEL GUIDANCE ENVELOPE IS TIGHTLY CLUSTERED, WITH SOME
SLIGHT VARIATION IN FORWARD SPEED. OVERALL, THIS FORECAST IS OF HIGH
CONFIDENCE.//
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