Tropical Storm NESAT Advisory Do, 20.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) WARNING NR
022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 17.6N 108.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 96 NM NORTH OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) AS THE SYSTEM CONTINUES
TO DECAY DUE TO STRONG VERTICAL WIND SHEAR (VWS) AND DRY AIR
ENTRAINMENT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE MSI LOOP, WHICH SHOWS A DEFINED LOW LEVEL CENTER, ALONG
WITH AGENCY DVORAK POSITION FIXES. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW DVORAK ESTIMATES OF
T1.5, AND RJTD AND KNES OF T2.0, ALONG WITH A COMBINATION OF
OBJECTIVE DVORAK INTENSITY FIXES. ENVIRONMENTAL CONDITIONS ARE
MARGINALLY UNFAVORABLE WITH DRY AIR ENTRAINMENT, MODERATE POLEWARD
OUTFLOW, WARM (27-28C) SEA SURFACE TEMPERATURES (SSTS), AND STRONG
(20-25KTS) VERTICAL WIND SHEAR (VWS).
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTH AND NORTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 25 KTS AT 192340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 23W (NESAT) IS FORECAST TO TRACK SLOWLY
NORTHWEST OVER THE NEXT 12 HOURS ALONG THE SOUTHWEST PERIPHERY OF
LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH
AND NORTHEAST. THE SYSTEM IS FORECAST TO TRACK IN MARGINALLY
UNFAVORABLE ENVIRONMENT WHILE DECAYING IN INTENSITY DUE TO HIGH
VERTICAL WIND SHEAR (VWS) ALONG WITH DRY COOL AIR ENTRAINING INTO
THE SYSTEM. AFTER TAU 12, THE SYSTEM WILL TURN AND TRACK
SOUTHWESTWARD AS THE SYSTEM CONTINUES TO WEAKEN THROUGH TAU 24.
AFTER TAU 24, THE TRACK MOTION IS FORECAST TO SLOW DOWN BEFORE
MAKING LANDFALL OVER EASTERN VIETNAM. THE SYSTEM WILL THEN BECOME
QUASI-STATIONARY AND THEN DISSIPATE BY TAU 36 OR SHORTLY THEREAFTER
AS ENVIRONMENTAL CONDITIONS QUICKLY DEGRADE FURTHER.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH THE EXCEPTION OF NAVGEM AND SUPPORTS THE JTWC FORECAST TRACK
WITH MEDIUM CONFIDENCE. THE 191800Z GFS (GEFS) ENSEMBLE ALSO
SUPPORTS THE LATEST TRACK FORECAST AND INDICATES STEADY WEAKENING
AND DISSIPATION. RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT
AND SHOWS A STEADY WEAKENING TREND THROUGH OUT THE FORECAST PERIOD
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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