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Tropical Storm CHANTAL


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TROPICAL STORM CHANTAL DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL032013
1100 PM AST MON JUL 08 2013
 
THE OVERALL CLOUD PATTERN OF CHANTAL HAS IMPROVED SLIGHTLY SINCE
THIS AFTERNOON...WITH MORE BANDING FEATURES EVIDENT IN CONVENTIONAL
SATELLITE IMAGERY.  THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT
INVESTIGATING CHANTAL FOUND A SMALL AREA OF LIGHT NORTHWEST AND
WEST WINDS SOUTH OF THE CENTER AND WERE THEREFORE ABLE TO CLOSE OFF
A CIRCULATION.  THE AIRCRAFT REPORTED MAXIMUM FLIGHT-LEVEL WINDS OF
58 KT AND BIAS-CORRECTED SFMR WINDS OF 40 TO 42 KT.  A BLEND OF THE
SFMR AND FLIGHT-LEVEL DATA YIELDS AN INITIAL WIND SPEED OF 45 KT.
THE AIRCRAFT REPORTED A SURPRISINGLY HIGH CENTRAL PRESSURE OF 1010
MB.
 
CHANTAL CONTINUES TO RACE RAPIDLY WEST-NORTHWESTWARD AT 23 KT. THE
STORM IS FORECAST TO CONTINUE ON THIS GENERAL HEADING AND FORWARD
SPEED DURING THE NEXT 24 HOURS OR SO...WITH SOME DECELERATE
EXPECTED AS IT APPROACHES HISPANIOLA IN 36 TO 48 HOURS.  AFTER THAT
TIME...A NORTHWESTWARD TURN AND A FURTHER REDUCTION IN FORWARD
SPEED IS FORECAST AS A BREAK IN THE RIDGE DEVLOPS OVER THE WESTERN
ATLANTIC.  AT DAYS 4 AND 5...CHANTAL IS EXPECTED TO MOVE SLOWLY
NORTH-NORTHWESTWARD OVER THE BAHAMAS AND WESTERN ATLANTIC
BETWEEN THE ATLANTIC RIDGE AND A DEVELOPING CUT-OFF LOW OVER
THE SOUTHEASTERN UNITED STATES. THE TRACK GUIDANCE IS IN GOOD
AGREEMENT DURING THE FIRST 48 HOURS OR SO OF THE FORECAST
PERIOD...BUT DIVERGES SOMEWHAT THEREAFTER.  THE LATEST GFS HAS
SHIFTED NORTHWARD AND IS NOW ALONG THE EASTERN EDGE OF THE GUIDANCE
ENVELOPE.  THE OFFICIAL FORECAST HAS BEEN NUDGED NORTHWARD AND
EASTWARD TO BE CLOSER TO THE MULTI-MODEL CONSENSUS...BUT IT LIES
SOUTH AND WEST OF THE LASTEST GFS AND ECMWF SOLUTIONS.
 
FAVORABLE ENVIRONMENTAL CONDITIONS SHOULD ALLOW FOR GRADUAL
STRENGTHENING BEFORE THE SYSTEM REACHES HISPANIOLA.  THE INTENSITY
GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 36 HOURS...AND THE
UPDATED INTENSITY FORECAST IS VERY SIMILAR TO THE PREVIOUS NHC
ADVISORY.  AFTER CHANTAL INTERACTS WITH HISPANIOLA...THE INTENSITY
FORECAST BECOMES QUITE UNCERTAIN.  THE CYCLONE SHOULD WEAKEN WHILE 
IT INTERACTS WITH LAND AND THE UPPER-LEVEL ENVIRONMENT BECOMES MUCH
LESS FAVORABLE.  ALTHOUGH NOT EXPLICITLY SHOWN IN THE FORECAST...
CHANTAL COULD WEAKEN BELOW TROPICAL STORM FORCE OR PERHAPS EVEN
DISSIPATE IN THE 3 TO 4 DAY TIME PERIOD.  NEAR THE END OF THE
FORECAST PERIOD...THE UPPER-LEVEL WINDS ARE FORECAST TO BECOME
CONDUCIVE FOR RESTRENGTHENING IF THE CYCLONE SURVIVES.  THE OFFICIAL
FORECAST ASSUMES THAT CHANTAL WILL REMAIN A TROPICAL CYCLONE AND
RE-INTENSIFY UNDER FAVORABLE CONDITIONS AROUND DAY 5.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/0300Z 12.4N  56.1W   45 KT  50 MPH
 12H  09/1200Z 13.7N  59.4W   50 KT  60 MPH
 24H  10/0000Z 15.3N  63.9W   55 KT  65 MPH
 36H  10/1200Z 17.1N  67.9W   60 KT  70 MPH
 48H  11/0000Z 19.0N  71.2W   50 KT  60 MPH
 72H  12/0000Z 22.5N  75.0W   35 KT  40 MPH
 96H  13/0000Z 25.5N  76.5W   35 KT  40 MPH
120H  14/0000Z 27.5N  77.5W   45 KT  50 MPH
 
$$
FORECASTER BROWN
 
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