000
WTNT43 KNHC 312030
TCDAT3
TROPICAL STORM CHANTAL DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032007
500 PM EDT TUE JUL 31 2007

CHANTAL IS MAINTAINING A CURVED BAND STRUCTURE ON VISIBLE SATELLITE
PICTURES...ALBEIT WITH LESS DEEP CONVECTION THAN EARLIER TODAY. 
THE STORM SHOULD SOON BEGIN THE EXTRATROPICAL TRANSITION PROCESS AS
SEA SURFACE TEMPERATURES BENEATH THE STORM SOON DECREASE BELOW 70F
AND IT INTERACTS WITH COOLER AIR OVER THE CANADIAN MARITIMES. 
SATELLITE CLASSIFICATIONS AND AMSU INTENSITY ESTIMATES SUPPORT
MAINTAINING THE INITIAL INTENSITY OF 45 KT.  COMPUTER
MODELS...ESPECIALLY THE GFS...FORECAST THE SYSTEM TO BECOME A
STRONG EXTRATROPICAL STORM IN ABOUT 3 DAYS AND A LITTLE
STRENGTHENING IS INDICATED AT THAT TIME.  

CHANTAL CONTINUES TO MOVE NORTHEASTWARD...WITH A 12 HOUR MOTION OF
ABOUT 23 KT.  A DEEPENING MIDDLE-LATITUDE STORM OVER EASTERN CANADA
SHOULD CONTINUE THE STORM'S MOTION TOWARD THE NORTHEAST WITH SOME
ACCELERATION.  MODEL GUIDANCE IS TIGHTLY CLUSTERED ON A TRACK
TAKING THE SYSTEM NEAR OR OVER THE AVALON PENINSULA OF NEWFOUNDLAND
AND THE OFFICIAL FORECAST REFLECT THIS SCENARIO.  

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      31/2100Z 41.7N  61.2W    45 KT
 12HR VT     01/0600Z 44.5N  57.3W    45 KT...BECOMING EXTRATROPICAL
 24HR VT     01/1800Z 48.6N  49.7W    45 KT...EXTRATROPICAL
 36HR VT     02/0600Z 53.5N  40.5W    45 KT...EXTRATROPICAL
 48HR VT     02/1800Z 57.0N  34.5W    45 KT...EXTRATROPICAL
 72HR VT     03/1800Z 60.0N  27.5W    50 KT...EXTRATROPICAL
 96HR VT     04/1800Z 62.0N  19.0W    40 KT...EXTRATROPICAL
120HR VT     05/1800Z 64.0N  12.0W    35 KT...EXTRATROPICAL
 
$$
FORECASTER BLAKE