Tropical Storm NESAT Advisory 10月15日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 18.8N 127.6E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 455 NM NORTHEAST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM WITH DEEP CONVECTIVE BANDING OVER THE WESTERN
PERIPHERY WRAPPING INTO AND OBSCURING THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON AN EARLIER PARTIAL 141259Z ASCAT-C IMAGE, WHICH
SHOWS AN ELONGATED BUT DEFINED CENTER WITH 20-25 KNOT WINDS OVER
THE NORTHERN PERIPHERY. THE INITIAL INTENSITY OF 25 KTS
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, RJTD DVORAK
ESTIMATES OF T1.5 AND ASCAT DATA. ENVIRONMENTAL CONDITIONS ARE
MARGINALLY FAVORABLE WITH MODERATE POLEWARD OUTFLOW, WARM (29-30C)
SEA SURFACE TEMPERATURES (SSTS), AND MODERATE (10-15KTS) VERTICAL
WIND SHEAR (VWS).
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 23W IS TRACKING WESTWARD ALONG
THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHEAST, AND WILL GRADUALLY TURN
WEST-NORTHWESTWARD THOUGH TAU 24. THE STR IS EXPECTED TO STRENGTHEN
TO THE NORTHEAST AND REALIGN TO A NORTHWEST-SOUTHEAST ORIENTATION
WHICH WILL TURN THE SYSTEM NORTHWESTWARD THROUGH TAU 48. A DEEP
MIDLATITUDE SHORTWAVE TROUGH WILL DIG OVER EASTERN CHINA BY TAU 48,
WHICH WILL ALSO HELP STEER THE SYSTEM IN A NORTHWEST DIRECTION
PASSING JUST NORTH OF LUZON. AFTER TAU 72, AS THE SHORTWAVE
TRANSITS EASTWARD, A DEEP LAYER RIDGE OVER EAST CHINA WILL THEN
BECOME THE MAIN STEERING FEATURE WHICH WILL ALSO INDUCE A
NORTHEASTERLY SURGE EVENT. THIS WILL RESULT IN THE SYSTEM TRACKING
SOUTHWESTWARD THEN WEST-SOUTHWESTWARD THROUGH THE REMAINED OF THE
FORECAST. TD 23W WILL STEADILY INTENSIFY THROUGH TAU 36 WITH RAPID
INTENSIFICATION POSSIBLE BETWEEN TAU 36 TO TAU 72, AS POLEWARD
OUTFLOW IMPROVES BY ENHANCED UPPER LEVEL WESTERLIES WHILE THE SYSTEM
TRACKS OVER WARM (29-30C) SSTS AND HIGH OCEAN HEAT CONTENT. BETWEEN
TAU 96 AND TAU 120, THE NORTHEASTERLY SURGE EVENT WILL INCREASE
VERTICAL WIND SHEAR (VWS) WHILE INCREASING DRY AIR AROUND THE SYSTEM
WHICH WILL RESULT IN STEADY WEAKENING THROUGH THE END OF THE
FORECAST.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH THE FORECAST PERIOD WITH A LARGE SPREAD OF 150-200NM FROM
TAU 72 TO TAU 120. THROUGH TAU 48 BOTH THE AVNI AND AEMI TRACKERS
ARE VERY CLOSE TO THE NORTHERN EDGE OF LUZON, BEFORE FOLLOWING
CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH TAU 120. ADDITIONALLY,
BETWEEN TAU 96 AND TAU 120 THE PRIMARY OUTLIERS ARE JGSM ON THE
SOUTHERN EDGE OF THE AIDS ENVELOPE, AND NVGM ON THE NORTHERN EDGE.
THE BULK OF THE ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS)
SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH TAU 48, WITH
INCREASING UNCERTAINLY AFTER TAU 72. THEREFORE, THE JTWC FORECAST
TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM
CONFIDENCE. THE RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT
AND SUPPORTS AN INTENSIFICATION PHASE WITH HWRF INDICATING A PEAK
INTENSITY NEAR 85 KNOTS AND COAMPS-TC (NAVGEM VERSION) A PEAK
INTENSITY OF 95 KNOTS, ABOVE THE INTENSITY CONSENSUS PEAK OF 80
KNOTS. GEFS INDICATES HIGH PROBABILITY OF MODERATE INTENSIFICATION
AND A 10 PERCENT CHANCE OF RAPID INTENSIFICATION (RI) BETWEEN TAU
48 AND TAU 72. AFTER TAU 72 THE INTENSITY GUIDANCE INCREASES IN
UNCERTAINTY DUE TO HOW THE SYSTEM INTERACTS WITH THE MODERATE
NORTHEAST SURGE EVENT. THEREFORE, THE JTWC FORECAST INTENSITY IS
PLACED WITH LOW CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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