Tropical Storm MALAKAS Advisory 4月9日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (MALAKAS)
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 6.5N 144.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 49 NM SOUTH-SOUTHEAST OF IFALIK
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CYCLONE BEING SHEARED FROM THE SOUTHEAST, WITH A RAGGED MASS OF
DEEP CONVECTION DISPLACED LARGELY NORTHWEST OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). A 081214Z ASCAT-B PASS REVEALED AN
ELONGATED CIRCULATION NEAR OR JUST EAST OF THE EASTERN EDGE OF THE
DEEP CONVECTION, WITH A WESTWARD EXTENSION TOWARD THE CONVECTION.
SINCE THAT TIME, EIR IMAGERY AND A 081847Z SSMIS MICROWAVE PASS
HAVE REVEALED THE CONVECTIVE AREA TO BE DOMINATED BY A SINGLE,
PERSISTENT UPDRAFT TO THE WEST OF THE LLCC, CHARACTERISTIC OF SOME
SHEARED TROPICAL CYCLONES. WITH NO APPARENT WRAPPING OF THE
CONVECTION AROUND THE LLCC, THIS STRUCTURE SUGGESTS THAT THE
CYCLONE IS NEAR STEADY-STATE. THE INITIAL INTENSITY REMAINS 40 KT
BASED ON A COMBINATION OF ASCAT DATA AND SUBJECTIVE DVORAK
INTENSITY ESTIMATES RANGING FROM T2.5 (35 KTS) TO T3.0 (45 KTS).
THIS IS ALSO CONSISTENT WITH A 081623Z AMSR-2 WIND SPEED ESTIMATE
OF 39 KT.
INITIAL WIND RADII BASIS: COMBINATION OF SCATTEROMETER DATA AND
PERSISTENCE
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   CIMSS SATCON: 47 KTS AT 081541Z
   CIMSS ADT: 43 KTS AT 081740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE WESTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THE ALTERNATE SCENARIO FOR A
SIGNIFICANTLY MORE WESTWARD TRACK DESCRIBED IN PREVIOUS WARNINGS IS
NO LONGER CONSIDERED A DISTINCT POSSIBILITY
FORECAST DISCUSSION: TROPICAL STORM 02W (MALAKAS) IS CURRENTLY
EMBATTLED BY UPPER-LEVEL SOUTHEASTERLY FLOW THAT MAXIMIZES AT 25 KT
AROUND 300 MB, JUST BELOW THE OUTFLOW LAYER, AS ANALYZED BY THE GFS
AND ECMWF MODELS. THE RESULTING CONVECTIVE STRUCTURE LACKS ANY
SIGNS OF PROGRESS TOWARD AXISYMMETRY, IMPLYING THAT MALAKAS MAY
STRUGGLE TO MAKE SIGNIFICANT GAINS IN INTENSITY DURING THE NEAR
TERM. HOWEVER, THE 300 MB ENVIRONMENTAL FLOW IS FORECAST TO
DECREASE TO 20 KT BY 24 HOURS, AND 15 KT BY 36 HOURS, LEADING TO A
DECREASE IN VERTICAL SHEAR THAT SHOULD ALLOW CONVECTION TO WRAP
FURTHER AROUND THE CIRCULATION CENTER AND FACILITATE
INTENSIFICATION. MALAKAS IS FORECAST TO REACH TYPHOON INTENSITY
AFTER 48 HOURS AND CONTINUE INTENSIFYING TO A PEAK OF 95 KT IN 96
HOURS IN AN ENVIRONMENT OF WEAK VERTICAL SHEAR AND WARM SEA SURFACE
TEMPERATURES. BEYOND 96 HOURS, THE CYCLONE WILL APPROACH COOLER
WATERS AROUND LATITUDE 19N AND POTENTIALLY BEGIN ENTRAINING AN
AMBIENT DRY SUBTROPICAL AIR MASS, WHICH SHOULD ARREST THE
INTENSIFICATION. THE TRACK FORECAST IS MORE STRAIGHT-FORWARD THAN
IN PREVIOUS WARNINGS, WITH MODEL GUIDANCE IN TIGHT AGREEMENT
THROUGH 48 HOURS, TAKING MALAKAS NORTHWESTWARD WELL SOUTHWEST OF
GUAM, STEERED BY THE DEEP-LAYER SUBTROPICAL RIDGE EAST OF THE
MARIANAS. A TURN NORTHWARD AROUND THE WESTERN PERIPHERY OF THIS
RIDGE IS EXPECTED AROUND 72 HOURS, AT WHICH POINT MODEL SPREAD
INCREASES. STEERING CURRENTS MAY WEAKEN AS THE MID-LATITUDE JET
REMAINS WELL NORTH OF THE CYCLONE AND A SHORTWAVE TROUGH CROSSES
KYUSHU AND BEGINS ERODING THE STEERING RIDGE. ADDITIONALLY, THE
POTENTIAL DEVELOPMENT OF INVEST 94W TO THE SOUTHWEST OF MALAKAS
COULD INDUCE A TEMPORARY WESTWARD JOG IN THE TRACK OF MALAKAS
DURING THE 72-96 HOUR PERIOD, DEPENDING ON HOW STRONG 94W BECOMES
AND THE EXACT PROXIMITY OF THE TWO CIRCULATIONS. SUCH A JOG, IF
ANY, IS EXPECTED TO BE SMALL GIVEN THE MUCH LARGER SIZE OF 02W
(MALAKAS). GIVEN THESE FACTORS, CONFIDENCE IN THE TRACK FORECAST
AFTER 72 HOURS IS MEDIUM.
MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH 48 HOURS AND SLIGHTLY WEST OF THE
PREVIOUS FORECAST, THEN SLIGHTLY RIGHT OF CONSENSUS BEYOND 48
HOURS, CLOSE TO THE MEAN OF ECMWF AND GFS, BUT A LITTLE SLOWER,
CLOSE TO THE PREVIOUS FORECAST. THE JTWC INTENSITY FORECAST IS
SLIGHTLY BELOW THE MULTI-MODEL CONSENSUS THROUGH 48 HOURS DUE TO
EXPECTED IMPEDIMENTS TO INTENSIFICATION. THE AGGRESSIVE HWRF
SOLUTION CALLS FOR TYPHOON INTENSITY IN 18 HOURS DUE TO A FORECAST
FOR RAPIDLY IMPROVING CONVECTIVE STRUCTURE, A FORECAST THAT IS NOT
VERIFYING AT PRESENT, AND IS CONSIDERED UNLIKELY.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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