Tropical Storm Chantal - 10pm Forecast Advisory

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM CHANTAL DISCUSSION NUMBER 9
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
1100 PM AST TUE JUL 09 2013

THE SATELLITE PRESENTATION OF CHANTAL BECAME LESS ORGANIZED DURING THE LATE AFTERNOON AND EARLY EVENING...BUT THERE HAS BEEN A BURST OF DEEP CONVECTION RECENTLY NEAR THE ESTIMATED CENTER. THE PLANE HAS HAD DIFFICULTY FIXING A CENTER...WITH THE WIND FIELD RESEMBLING AN OPEN WAVE RATHER THAN A CLOSED CIRCULATION. HOWEVER...AIR SPACE RESTRICTIONS PREVENTED THE PLANE FROM SAMPLING THE AREA FARTHER SOUTH...SO IT IS INCONCLUSIVE AS TO WHETHER A CLOSED CIRCULATION STILL EXISTS. AIRCRAFT DATA ALSO SUGGEST THAT SOME WEAKENING HAS TAKEN PLACE...WITH PEAK 850 MB FLIGHT-LEVEL AND BIAS-CORRECTED SFMR WINDS OF 50 AND 42 KT...RESPECTIVELY. THE INITIAL INTENSITY IS LOWERED TO 50 KT FOR THIS ADVISORY...WHICH COULD BE GENEROUS.

THE RAPID FORWARD MOTION OF CHANTAL COULD SUGGEST THAT WESTERLY LOW- TO MID-LEVEL SHEAR IS AFFECTING THE CYCLONE...AS SHOWN BY SHIPS AND UW-CIMSS ANALYSES. THE SHEAR SHOULD LIMIT ANY ADDITIONAL INTENSIFICATION PRIOR TO THE CENTER MOVING OVER OR NEAR HISPANIOLA. INTERACTION WITH THE MOUNTAINOUS TERRAIN OF THAT ISLAND SHOULD DISRUPT THE CIRCULATION ENOUGH TO CAUSE SIGNIFICANT WEAKENING OR EVEN POSSIBLY DISSIPATION. WHATEVER REMAINS OF CHANTAL AFTER THAT WILL ENCOUNTER HOSTILE UPPER-LEVEL WESTERLY WINDS ASSOCIATED WITH A MID- TO UPPER-LEVEL CYCLONIC SHEAR AXIS OVER THE SOUTHWESTERN ATLANTIC IN ABOUT 48 HOURS. THE GFS SUGGESTS A DECOUPLING OF THE LOW- TO MID-LEVEL CENTERS...WHILE ECMWF MAINTAINS MORE VERTICAL INTEGRITY. IF THE CYCLONE SURVIVES INTERACTION WITH LAND AND STRONG SHEAR...IT COULD REGENERATE OR RESTRENGTHEN LATE IN THE PERIOD. IT SHOULD BE NOTED THAT THERE IS SIGNIFICANT UNCERTAINTY IN THE INTENSITY FORECAST IN THE 3 TO 5 DAY PERIOD.

ABSENT RELIABLE CENTER FIXES...THE SPEEDY INITIAL MOTION ESTIMATE... 285/25...OF CHANTAL IS QUITE UNCERTAIN. BASED ON AVAILABLE AIRCRAFT DATA THE CENTER IS RELOCATED A BIT TO THE SOUTH RELATIVE TO THE PREVIOUS TRACK...WHICH HAS A RESULTED IN SOUTHWARD AND WESTWARD SHIFT OF THE FORECAST TRACK THROUGH 36 HOURS. A STRONG
SUBTROPICAL RIDGE GUIDING CHANTAL RAPIDLY WEST-NORTHWESTWARD IS FORECAST TO WEAKEN AND SHIFT EASTWARD AS A PRONOUNCED WEAKNESS DEVELOPS ALONG THE UNITED STATES EAST COAST AND EXTENDS SOUTHWARD
INTO FLORIDA. THIS SHOULD RESULT IN THE TRACK OF CHANTAL BENDING NORTHWESTWARD AND THEN NORTHWARD AFTER 36 HOURS. THE OFFICIAL TRACK FORECAST LEANS ON THE WEAKER GFS SOLUTION WHICH HAS A SHALLOWER CYCLONE BEYOND 48 HOURS.


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