Tropical Storm NANMADOL Advisory 9月15日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANMADOL) WARNING NR
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 23.1N 139.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 131 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS CONTINUING
IMPROVEMENT AND CONSOLIDATION OF BROAD FLARING CONVECTIVE BANDING
WRAPPING AROUND THE SYSTEM INTO A DEEPENING LOW LEVEL CIRCULATION
CENTER (LLCC). SATELLITE IMAGERY ALSO REVEALS THAT 16W HAS MADE THE
LEFT TURN WHILE INCREASING TRACK SPEED AS IT TRANSITS
WEST-NORTHWEST. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON AN EARLIER EXTRAPOLATED 131141Z METOP-C ASCAT,
ALONG WITH A COMBINATION OF AGENCY FIX POSITIONS FROM PGTW, KNES,
AND RJTD. THE INITIAL INTENSITY IS PLACED WITH HIGH CONFIDENCE
BASED ON THE IMPROVED SATELLITE DEPICTION, ALONG WITH THE PGTW
DVORAK ESTIMATE OF T3.0, WITH THE LATEST CIMSS SATCON VALUE COMING
IN AT 53 KNOTS. THEREFORE, THE CURRENT INTENSITY IS UPGRADED TO 50
KNOTS.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: THE SUBTROPICAL RIDGE TO THE NORTH
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 53 KTS AT 141810Z
   CIMSS ADT: 47 KTS AT 141740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DEEP TROPICAL MOISTURE INFLOW
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TS 16W (NANMADOL) IS FORECAST TO TRACK
NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE
(STR) WHICH WILL REMAIN THE DOMINATE STEERING FEATURE TO THE NORTH.
THE ENVIRONMENTAL FACTORS ARE CONDUCIVE FOR FURTHER DEVELOPMENT
CHARACTERIZED BY LOW (0-5 KTS) VERTICAL WIND SHEAR (VWS), WARM
(29-30C) SEA SURFACE TEMPERATURES (SSTS) AND MODERATE RADIAL
OUTFLOW. THESE FACTORS WILL ALLOW 16W TO CONTINUE A STEADY INCREASE
IN INTENSIFICATION BEFORE REACHING A POTENTIAL MAXIMUM INTENSITY OF
105 KNOTS BY TAU 72, WHILE THE SYSTEM ROUNDS THE SUBTROPICAL RIDGE
AXIS AND TURNS NORTH-NORTHWEST. BETWEEN TAU 72 AND TAU 96 TS 16W
WILL BEGIN TO SLOW IN TRACK SPEED, AS MANY MODEL TRACKERS INDICATE
A POSSIBLE RECURVE SCENARIO WITH SOME SPREAD OF 125 NM.
ADDITIONALLY, THE JTWC FORECAST CALLS FOR A DECREASE IN INTENSITY
TO 80 KNOTS LIKELY DUE TO THE AFFECT OF LAND INTERACTION ALONG WITH
AN INCREASE IN VERTICAL WIND SHEAR (VWS), AS DECAY SHIPS GUIDANCE
INDICATES UP TO 15 KNOTS. BETWEEN TUA 96 AND TAU 120, THE SYSTEM IS
FORECAST TO CONTINUE TO RECURVE AS 16W MOVES POLEWARD OF THE RIDGE
AXIS AND BECOMES EMBEDDED IN AN APPROACHING UPPER LEVEL TROUGH
WHICH WOULD INCREASE ITS TRACK SPEED TO THE NORTHEAST. HOWEVER,
THERE IS UNCERTAINTY IN THE TIMING OF THE INTERACTION WITH THE
APPROACHING UPPER LEVEL TROUGH AND HOW FAST THE SUBTROPICAL RIDGE
TO THE EAST ERODES. THESE FACTORS WILL HAVE A LARGE IMPACT ON THE
TRACK MOTION AND TRACK SPEED BY THE END OF THE FORECAST.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT THROUGH
TAU 72 WITH ONLY AN 80NM SPREAD IN SOLUTIONS. BY TAU 96 THE
CONSENSUS SPREAD INCREASES TO 125NM. BEYOND TAU 96, UNCERTAINTY
INCREASES WITH DIFFERENCES IN THE TIMING AND POSITION OF A POSSIBLE
RECURVATURE WITH MODEL TRACKERS DIVERGING GREATLY. FOR EXAMPLE, THE
LATEST GFS NUMERICAL MODEL GUIDANCE SHOWS A SLOW DOWN IN TRACK
SPEED TO A POSSIBLE QUASI-STATIONARY SOLUTION TO THE SOUTHWEST OF
JAPAN. WHILE OTHER MODELS SUCH AS ECMWF, UKMO, AND GALWEM TAKE A
SHARPER TURN TOWARDS HONSHU WHILE INCREASING IN TRACK SPEED BY TAU
120. GIVEN THESE TWO POSSIBLE SCENARIOS UNCERTAINTY REMAINS HIGH IN
THE TRACK FORECAST FROM TAU 96 THROUGH TAU 120. RELIABLE INTENSITY
GUIDANCE IS IN GOOD AGREEMENT WITH ALL MEMBERS SHOWING A STEADY
INTENSIFICATION THROUGH TAU 72. HOWEVER, RAPID INTENSIFICATION IS A
POSSIBILITY OVER THE NEXT 36 TO 72 HOURS, AND WILL CONTINUE TO BE
MONITORED FOR THE POSSIBILITY WITH AN ADJUSTMENT IN THE MAXIMUM
INTENSITY AS MORE GUIDANCE BECOMES AVAILABLE. FROM TAU 96 THROUGH
120, THE FORECAST INTENSITY CONFIDENCE IS LOW GIVEN THE UNCERTAINTY
AND DIFFERENCES IN THE TIMING AND SPEED OF THE INTERACTION WITH
LARGE SCALE STEERING FEATURES AS WELL AS LAND INTERACTION.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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