Tropical Storm Chantal - 10pm Monday Advisory

By: National Hurricane Center
By: National Hurricane Center

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 ANDWEST 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.


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