000
WTNT43 KNHC 100254
TCDAT3

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.   

FORECAST POSITIONS AND MAX WINDS

INIT  10/0300Z 15.3N  66.2W   50 KT  60 MPH
 12H  10/1200Z 16.7N  69.3W   50 KT  60 MPH
 24H  11/0000Z 18.6N  72.8W   40 KT  45 MPH
 36H  11/1200Z 20.6N  75.1W   35 KT  40 MPH...OVER LAND
 48H  12/0000Z 22.6N  76.6W   35 KT  40 MPH...OVER WATER
 72H  13/0000Z 26.5N  78.0W   35 KT  40 MPH
 96H  14/0000Z 29.0N  79.5W   35 KT  40 MPH
120H  15/0000Z 31.0N  81.0W   40 KT  45 MPH

$$
FORECASTER KIMBERLAIN/BROWN