Sunday,  September 9, 2012

TROPICAL STORM LESLIE

TROPICAL STORM LESLIE DISCUSSION NUMBER  41
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
1100 AM AST SUN SEP 09 2012

LESLIE HAS A VERY BROAD EYE AS EVIDENCED BY BERMUDA RADAR
OBSERVATIONS AND SATELLITE IMAGES.  A RECENT ASCAT PASS OVER THE
TROPICAL CYCLONE SHOWED 40-45 KT WINDS...AND ENHANCED IR DATA SHOWED
SOME INCREASE IN THE DEEP CONVECTION IN CLUSTERS SURROUNDING THE
CENTER.  THE CURRENT INTENSITY IS HELD AT 50 KT FOR THIS ADVISORY.
SINCE LESLIE LACKS A WELL-DEFINED INNER CORE...IT MAY HAVE
DIFFICULTY RE-INTENSIFYING AS IT MOVES FARTHER AWAY FROM THE COOLER
WATERS IT UPWELLED.  HOWEVER...UPPER-TROPOSPHERIC WINDS ARE
FORECAST TO BE FAVORABLE FOR STRENGTHENING DURING THE NEXT DAY OR
SO...AND THE OFFICIAL WIND SPEED FORECAST SHOWS THE CYCLONE
REGAINING HURRICANE STATUS AS IN THE PREVIOUS ADVISORY.  THIS IS
ALSO IN GOOD AGREEMENT WITH THE LATEST LGEM GUIDANCE.  BEYOND 48
HOURS...THE GLOBAL MODELS DEPICT LESLIE TO BE QUITE DEEP BUT
BECOMING EMBEDDED WITHIN A FRONTAL ZONE...SO THE SYSTEM IS FORECAST
TO BECOME A VIGOROUS EXTRATROPICAL CYCLONE IN 2-3 DAYS AS IT MOVES
OVER THE ATLANTIC.  BY DAY 5 THE SYSTEM IS LIKELY TO MERGE WITH A
LARGE LOW TO THE NORTHWEST OF SCANDANAVIA.

LESLIE IS BEGINNING TO INCREASE ITS FORWARD SPEED...AND THE INTIAL
MOTION IS ESTIMATED TO BE 010/9.  AS A MID-TROPOSPHERIC TROUGH
MOVES OFF THE NORTHEAST U.S. COAST...THE CYCLONE IS EXPECTED TO
ACCELERATE NORTH-NORTHEASTWARD IN THE FLOW ON THE EAST SIDE OF THE
TROUGH OVER THE NEXT COUPLE OF DAYS.  IN 3-4 DAYS...THE POST-
TROPICAL CYCLONE SHOULD TURN EAST-NORTHEASTWARD IN THE HIGHER
LATITUDE WESTERLIES.  THE OFFICIAL TRACK FORECAST IS SOMEWHAT
FASTER THAN THE PREVIOUS ONE IN THE LATTER PART OF THE FORECAST
PERIOD...BUT NOT AS FAST AS THE LATEST GFS SOLUTION.   

LONG-PERIOD SWELLS FROM LESLIE ARE EXPECTED TO PRODUCE ROUGH SURF
AND LIFE-THREATENING RIP CURRENTS ON BERMUDA AND ALONG MUCH OF THE
U.S. EAST COAST FOR THE NEXT FEW DAYS.

FORECAST POSITIONS AND MAX WINDS

INIT  09/1500Z 32.0N  62.4W   50 KT  60 MPH
 12H  10/0000Z 33.6N  62.0W   55 KT  65 MPH
 24H  10/1200Z 36.3N  60.9W   60 KT  70 MPH
 36H  11/0000Z 40.2N  59.0W   65 KT  75 MPH
 48H  11/1200Z 46.5N  55.5W   65 KT  75 MPH
 72H  12/1200Z 58.0N  42.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  13/1200Z 62.0N  20.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  14/1200Z...MERGED

91L off the coast of Africa

A tropical wave that emerged off the coast of Africa on Friday (Invest 91L) is 250 miles west of the Cape Verde Islands, and is headed west-northwest at 10 – 15 mph. The disturbance is large with plenty of spin, but has limited heavy thunderstorm activity due to dry air. Most of the reliable computer models are predicting that 91L will develop into a tropical depression by Wednesday. In their 8 am EDT Tropical Weather Outlook, NHC gave 91L a 40% chance of developing into a tropical depression by Tuesday morning. Our two most reliable models, the GFS and ECMWF, predict that 91L will pass at least 500 miles to the northeast of the Lesser Antilles Islands late this week, on a track that would likely keep this storm far out at sea away from any land areas.

(Source: Weatherunderground.com)