WTPQ30 RJTD 071200
RSMC TROPICAL CYCLONE PROGNOSTIC REASONING
REASONING NO.13 FOR TY 2014 CHAN-HOM (2014)
1.GENERAL COMMENTS
TY CHAN-HOM IS LOCATED AT 26.5N, 133.9E. INFORMATION ON THE
CURRENT POSITION IS BASED ON ANIMATED MSI AND SURFACE
OBSERVATIONS. POSITIONAL ACCURACY IS GOOD. CENTRAL PRESSURE IS
970HPA AND MAXIMUM SUSTAINED WINDS NEAR THE CENTER ARE 65KNOTS.
THE SYSTEM IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT UNDER THE
INFLUENCE OF HIGH SSTS, HIGH TCHP AND WEAK VWS. HOWEVER, THE
LIMITED FIRMNESS OF ITS STRUCTURE HAS CAUSED IT TO MAINTAIN ITS
INTENSITY OVER THE LAST SIX HOURS. INFORMATION ON THE CURRENT
INTENSITY IS BASED ON DVORAK INTENSITY ANALYSES AND SURFACE
OBSERVATIONS.
2.SYNOPTIC SITUATION
THE SYSTEM IS MOVING NORTHWESTWARD BETWEEN TWO MID-LEVEL
SUB-TROPICAL HIGHS. ANIMATED MSI SHOWS THE ELONGATION OF 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 NORTHWESTWARD ALONG THE PERIPHERY OF A
MID-LEVEL SUB-TROPICAL HIGH UNTIL FT12. THE SYSTEM WILL THEN
GRADUALLY DECELERATE AND MOVE NORTHWARD DUE TO WEAK STEERING FLOW
UNTIL FT48. THE SYSTEM WILL THEN GRADUALLY ACCELERATE AND MOVE
EAST-NORTHEASTWARD UNDER THE INFLUENCE OF MID-LATITUDE PREVAILING
WESTERLIES UNTIL FT120. THE TRACK FORECAST IS BASED ON GSM
PREDICTIONS, AND REFERENCE TO OTHER NWP MODELS. TRACK FORECAST
CONFIDENCE IS FAIR UNTIL FT72 BUT LOW THEREAFTER DUE TO
SIGNIFICANT DIFFERENCES AMONG NWP MODEL OUTPUTS.
4.INTENSITY FORECAST
THE SYSTEM WILL DEVELOP UNTIL FT24 DUE TO THE INFLUENCE OF
INTERACTION WITH HIGH SSTS, HIGH TCHP, WEAK VWS AND GOOD UPPER
LEVEL OUTFLOW. THE SYSTEM WILL THEN WEAKEN UNTIL FT72 DUE TO THE
INFLUENCE OF INTERACTION WITH LOWER SSTS, REDUCED TCHP AND
INCREASED VWS. THE SYSTEM WILL THEN WEAKEN UNTIL FT120 DUE TO THE
INFLUENCE OF INTERACTION WITH LOW SSTS, LOW TCHP, STRONG VWS AND
LAND. THE SYSTEM WILL TRANSFORM INTO AN EXTRATROPICAL CYCLONE BY
FT120. THE INTENSITY FORECAST IS BASED ON A CONSENSUS OF GUIDANCE
DATA INCLUDING GSM.
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