WTPQ30 RJTD 091200
RSMC TROPICAL CYCLONE PROGNOSTIC REASONING
REASONING NO. 7 FOR TS 2021 ETAU (2021)
1.GENERAL COMMENTS
TS ETAU IS LOCATED AT 12.1N, 111.6E. INFORMATION ON THE CURRENT
POSITION IS BASED ON ANIMATED MSI AND SURFACE OBSERVATIONS.
POSITIONAL ACCURACY IS FAIR. CENTRAL PRESSURE IS 996HPA AND
MAXIMUM SUSTAINED WINDS NEAR THE CENTER ARE 40KNOTS. THE SYSTEM IS
IN AN UNFAVORABLE ENVIRONMENT FOR DEVELOPMENT UNDER THE INFLUENCE
OF LOWER SSTS AND REDUCED TCHP. THIS HAS CAUSED THE SYSTEM TO
WEAKEN OVER THE LAST SIX HOURS. HOWEVER, THE INFLUENCE OF WEAK VWS
IS FAVORABLE FOR SYSTEM DEVELOPMENT. INFORMATION ON THE CURRENT
INTENSITY IS BASED ON DVORAK INTENSITY ANALYSES AND SURFACE
OBSERVATIONS.
2.SYNOPTIC SITUATION
THE SYSTEM IS MOVING WEST-SOUTHWESTWARD ALONG THE SOUTHERN
PERIPHERY OF A MID-LEVEL SUB-TROPICAL HIGH. ANIMATED MSI SHOWS THE
SYSTEM HAS A BAND WITH A CURVATURE SUGGESTING THE CSC. ANIMATED
MSI SHOWS GOOD CLOUD CHARACTERISTICS OF ANTICYCLONIC OUTFLOW.
WATER VAPOR IMAGERY SHOWS DRY AIR IN THE DIRECTION OF THE
MOVEMENT. DMSP-F18/SSMIS 89 GHZ MICROWAVE IMAGERY SHOWS THE SYSTEM
HAS A BAND WITH CURVATURE INDICATING THE CSC.
3.TRACK FORECAST
THE SYSTEM WILL MOVE WESTWARD ALONG THE PERIPHERY OF A MID-LEVEL
SUB-TROPICAL HIGH UNTIL FT24. THE SYSTEM WILL HIT VIET-NAM BY
FT18. THE TRACK FORECAST IS BASED ON GSM PREDICTIONS, AND
REFERENCE TO OTHER NWP MODELS. TRACK FORECAST CONFIDENCE IS FAIR
UNTIL FT12 BUT LOW THEREAFTER DUE TO SIGNIFICANT DIFFERENCES AMONG
NWP MODEL OUTPUTS.
4.INTENSITY FORECAST
THE SYSTEM WILL MAINTAIN ITS INTENSITY UNTIL FT12 DUE TO THE
INFLUENCE OF INTERACTION WITH LOWER SSTS, REDUCED TCHP AND WEAK
VWS. THE SYSTEM WILL THEN WEAKEN UNTIL FT24 DUE TO ITS LANDFALL.
THE SYSTEM WILL WEAKEN TO TD INTENSITY BY FT24. THE INTENSITY
FORECAST IS BASED ON A CONSENSUS OF GUIDANCE DATA INCLUDING GSM.
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