[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 241158
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT SEP 24 2011

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1115 UTC.

...SPECIAL FEATURES...

TROPICAL STORM OPHELIA IS CENTERED NEAR 16.9N 55.2W AT 24/0900
UTC OR ABOUT 380 NM E OF THE LEEWARD ISLANDS MOVING NW AT 12 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED
WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. PLEASE SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
FOR MORE DETAILS. OPHELIA HAS NOT CHANGED MUCH OVER THE PAST FEW
HOURS WITH THE CENTER MOSTLY EXPOSED DUE TO MODERATE TO STRONG
SW SHEAR THAT SHOULD REMAIN IN PLACE FOR THE NEXT SEVERAL DAYS
DUE TO A UPPER LEVEL TROUGH TO THE W OF OPHELIA. SCATTERED
MODERATE/ STRONG CONVECTION IS E OF THE CENTER WITHIN 75/90 NM
OF LINE FROM 14N52W 18N51W TO 21N54W AND SW OF THE CENTER WITHIN
A 60 NM RADIUS OF 15N56W.

THE 1008 MB LOW THAT IS S OF THE CAPE VERDE ISLANDS HAS BEEN
UPGRADED TO TROPICAL DEPRESSION SEVENTEEN AT 24/0900 UTC.
TROPICAL DEPRESSION SEVENTEEN IS CENTERED NEAR 10.7N 25.2W AT
24/0900 UTC OR ABOUT 250 NM S OF THE SOUTHERNMOST CAPE VERDE
ISLANDS MOVING W AT 13 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS
1007 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40
KT. PLEASE SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. T.D. SEVENTEEN
HAS DISTINCT CURVED BANDS ON VISIBLE SATELLITE IMAGERY. A BAND
OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 45 NM
OF LINE FROM 9N26W 11N26W TO 13N24W.

...TROPICAL WAVES...

TROPICAL WAVE IS ANALYZED ALONG 37W/38W BETWEEN 9N-19N MOVING W
AT 10-15 KT. WAVE IS WELL DEFINED IN THE UPPER LEVEL SATELLITE
WINDS AND IN THE LOW CLOUDS ON SATELLITE IMAGERY. WAVE REMAINS
EMBEDDED WITHIN AN AREA OF DEEP LAYER MOISTURE AS SEEN ON THE
TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED SHOWERS ARE WITHIN
75 NM EITHER SIDE OF THE WAVE AXIS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS AFRICA WITH A PORTION OF THE
TROUGH EXTENDING FROM 13N21W THROUGH WHAT IS NOW T.D. SEVENTEEN
ALONG 8N28W TO 7N35W. SMALL CLUSTER OF SCATTERED MODERATE/
ISOLATED STRONG CONVECTION IS WITHIN 60 NM 0F 10N BETWEEN
32W-33W.

...DISCUSSION...

GULF OF MEXICO...
THE WEAKENING COLD FRONT EXTENDS INTO THE GULF ACROSS THE
FLORIDA PANHANDLE JUST W OF TALLAHASSEE ALONG 28N86W TO 26N89W
SUPPORTED BY AN UPPER TROUGH THAT COVERS E CONUS FROM THE
MISSISSIPPI VALLEY TO THE EASTERN SEABOARD AND INTO THE GULF N
OF 23N. THE N GULF IS DOMINATED BY STRONG SUBSIDENCE AND DRY
STABLE AIR THUS THE FRONT IS CURRENTLY DRY. AN UPPER RIDGE
EXTENDS FROM THE E PACIFIC REGION ACROSS MEXICO COVERING THE SW
GULF AND THE BAY OF CAMPECHE. A SURFACE TROUGH EXTENDS FROM THE
E GULF NEAR 27N85W TO OVER THE NW YUCATAN PENINSULA NEAR 21N90W
TO THE N BORDER OF GUATEMALA GENERATING SCATTERED SHOWERS AND
POSSIBLE ISOLATED THUNDERSTORMS S OF 27N BETWEEN 83W-87W AND IN
THE E BAY OF CAMPECHE S OF 20N E OF 93W TO INLAND OVER THE
YUCATAN PENINSULA. THE NW GULF REMAINS UNDER CLEAR SKIES THIS
MORNING. THE WEAK COLD FRONT WILL REACH FROM THE FLORIDA BIG
BEND REGION TO THE CENTRAL GULF LATER TODAY THEN STALL WHILE
SLOWLY DISSIPATING THROUGH MON. HIGH PRESSURE WILL BUILD IN THE
WAKE OF THE FRONT SUN THROUGH TUE AND SHIFT N WED.

CARIBBEAN SEA...
AN UPPER RIDGE COVERS THE SW CARIBBEAN S OF 17N W OF 70W WHILE
AN UPPER TROUGH FROM THE SW ATLC COVERS THE E CARIBBEAN.
EASTERLY SURFACE WIND COMBINED WITH THE DIFFLUENT ENVIRONMENT
ALOFT OVER THE CENTRAL CARIBBEAN ARE GENERATING CLUSTERS OF
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS MAINLY FROM 12N-20N W
OF 75W TO OVER CENTRAL AMERICA AND IN THE GULF OF HONDURAS. THE
MONSOON TROUGH EXTENDS ACROSS THE SW CARIBBEAN FROM COLOMBIA
NEAR 9N76W ALONG 11N81W INTO THE E PACIFIC REGION ACROSS COSTA
RICA/NICARAGUA BORDER GENERATING SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS S OF 12N BETWEEN 75W-84W. THIS IS LEAVING THE E
CARIBBEAN UNDER MOSTLY CLEAR SKIES THIS MORNING. TROPICAL STORM
OPHELIA WILL CONTINUE TO MOVE NE OF THE LEEWARD ISLANDS SAT
NIGHT THROUGH MON.

ATLANTIC OCEAN...
A SMALL UPPER RIDGE IS ANCHORED OVER THE FAR W ATLC NEAR THE
CENTRAL BAHAMAS PROVIDING A DIFFLUENT ENVIRONMENT ALOFT WHILE A
SURFACE TROUGH EXTENDS FROM 30N78W ACROSS GRAND BAHAMA ISLAND TO
THE N COAST OF CUBA NEAR 23N79W. HEAVY SHOWERS AND NUMEROUS
THUNDERSTORMS COVER THE S BAHAMA ISLANDS TO OVER THE TURKS AND
CAICOS FROM 20N-23N BETWEEN 72W-74W WHILE SCATTERED SHOWERS/
ISOLATED THUNDERSTORMS COVER THE REMAINDER OF THE AREA S OF 32N
BETWEEN 73W-80W. A BROAD UPPER RIDGE DOMINATES THE W ATLC
ANCHORED ABOUT 150 NM NW OF BERMUDA PROVIDING DRY STABLE AIR
OVER THE AREA N OF 25N BETWEEN 40W-73W. AN UPPER TROUGH EXTENDS
FROM AN UPPER LOW IN THE SW ATLC NEAR 22N67W TO OVER THE E
CARIBBEAN PRODUCING ISOLATED SHOWERS AND POSSIBLE ISOLATED
THUNDERSTORMS FROM 19N-22N BETWEEN 62W-70W. A BROAD SURFACE
RIDGE DOMINATES THE REMAINDER OF THE ATLC N OF 20N W OF 75W
ANCHORED BY A SERIES OF HIGHS N OF THE DISCUSSION AREA. THE
SURFACE TROUGH WILL REMAIN NEARLY STATIONARY AND GRADUALLY
DISSIPATE TONIGHT. TROPICAL STORM OPHELIA WILL CONTINUE TO MOVE
NE OF THE LEEWARD ISLANDS SAT NIGHT BEING N OF THE VIRGIN
ISLANDS MON NIGHT BEFORE TURNING MORE NORTHWARD.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
PAW






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