Tropical Storm Chantal - 10am Monday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM CHANTAL DISCUSSION NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
1100 AM AST MON JUL 08 2013

CONVECTIVE ORGANIZATION OF HAS IMPROVED SLIGHTLY IN SATELLITE IMAGERY SINCE THE PREVIOUS ADVISORY WITH FRAGMENTED CURVED BANDS DEVELOPING IN THE NORTHERN SEMICIRCLE...ALTHOUGH THE CORE CONVECTION HAS WEAKENED SOME. THE INITIAL INTENSITY OF 40 KT IS BASED ON A BLEND OF TAFB...SAB...ADT...AND AMSU SATELLITE INTENSITY ESTIMATES. VISIBLE AND WATER VAPOR IMAGERY ALSO INDICATE THAT CHANTAL HAS DEVELOPED SOME WEAK ANTICYCLONIC OUTFLOW.

THE INITIAL MOTION ESTIMATE REMAINS A RATHER BRISK 280/23 KT. NO CHANGES WERE MADE TO THE PREVIOUS FORECAST TRACK. CHANTAL IS FORECAST TO MOVE QUICKLY WEST-NORTHWESTWARD TO THE SOUTH OF A STRONG DEEP-LAYER SUBTROPICAL RIDGE FOR THE NEXT 48 HOURS. BY DAY 3 AND BEYOND...A VIGOROUS MID-/UPPER-LEVEL LOW CURRENTLY JUST EAST OF THE BAHAMAS IS EXPECTED TO MOVE WESTWARD AND MERGE WITH A MID-LATITUDE TROUGH...CREATING A BREAK IN THE SUBTROPICAL RIDGE OVER THE SOUTHEASTERN U.S. AND THE BAHAMAS. CHANTAL IS FORECAST TO SLOW DOWN AND TURN NORTHWESTWARD BY 72 HOURS AS IT APPROACHES THIS DEVELOPING WEAKNESS IN THE RIDGE...AND THEN MOVE SLOWLY NORTH-NORTHWESTWARD THROUGH THE WEAKNESS ON DAYS 4 AND 5. THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE LEFT OF THE MODEL CONSENSUS AND LIES ALONG THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE...CLOSE TO THE GFS AND FSSE MODELS.

OTHER THAN THE FAST FORWARD SPEED OF CHANTAL...ENVIRONMENTAL CONDITIONS ARE FAIRLY FAVORABLE FOR AT LEAST SOME MODEST STRENGTHENING TO OCCUR DURING THE NEXT 48 HOURS OR SO WHILE THE
CYCLONE REMAINS UNDERNEATH A 200 MB RIDGE AXIS. INTERACTION WITH THE MOUNTAINOUS TERRAIN OF HISPANIOLA AND EASTERN CUBA IN ABOUT THREE DAYS...COUPLED WITH INCREASING WESTERLY VERTICAL WIND SHEAR...IS EXPECTED TO CAUSED TO CHANTAL TO WEAKEN CONSIDERABLY BY
DAY 3...AND CONTINUE INTO DAYS 4 AND 5 AS THE CYCLONE MOVES UNDERNEATH AN UPPER-LEVEL TROUGH. THE OFFICIAL INTENSITY FORECAST FOLLOWS THE ICON INTENSITY CONSENSUS MODEL AND THE FSSE MODEL.


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