[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 252356
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT AUG 25 2012

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2315 UTC.

...SPECIAL FEATURES...

THE CENTER OF TROPICAL STORM ISAAC AT 26/0000 UTC IS NEAR 21.7N
76.7W. THIS POSITION IS ABOUT 70 NM ENE OF CAMAGUEY CUBA...AND
ABOUT 325 NM ESE OF KEY WEST FLORIDA. ISAAC IS MOVING NW AT 17
KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 997 MB. THE
MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT.
PLEASE READ THE FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC AND THE PUBLIC ADVISORY...MIATCPAT4/WTNT34
KNHC FOR MORE DETAILS. THE RAIN IMPACTS OF ISAAC SPREAD ACROSS A
LARGE AREA FROM THE CARIBBEAN ALL THE WAY INTO THE SE GULF OF
MEXICO. CURRENTLY NUMEROUS MODERATE/ISOLATED STRONG CONVECTION
IS FROM 15N-21N BETWEEN 69W-74W...INCLUDING MUCH OF HISPANIOLA.
SIMILAR ACTIVITY IS N OF CUBA INTO THE FLORIDA STRAITS FROM
22N-25N BETWEEN 76W-81W. ELSEWHERE...SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS FROM 18N-26N BETWEEN 67W-85W...INCLUDING
PORTIONS OF PUERTO RICO...CUBA...THE BAHAMAS...AND SOUTHERN
FLORIDA.

TROPICAL WAVE EXTENDS FROM 21N31W TO A 1009 MB SURFACE LOW NEAR
15N32W MOVING WNW NEAR 15 KT. THE WAVE/LOW LIES WITHIN A LARGE
SURGE OF DEEP LAYER MOISTURE PRESENT ACROSS MUCH OF THE EASTERN
TROPICAL ATLC. BROAD CYCLONIC FLOW IS AROUND THE WAVE/LOW AND
THE MONSOON TROUGH AND THE SYSTEM HAS BECOME SLIGHTLY MORE
ORGANIZED TODAY. CURRENTLY SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 13N-20N BETWEEN 28W-36W. DEVELOPMENT OF THIS
SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF DAYS.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF
MAURITANIA AT 20N16W CONTINUING TO A 1009 MB SURFACE LOW
CONNECTED TO A TROPICAL WAVE AT 15N32W AND ALONG 10N39W 10N48W.
THE ITCZ BEGINS AT 10N48W TO 12N60W. SCATTERED MODERATE
CONVECTION IS FROM 8N-10N BETWEEN 38W-44W.

...DISCUSSION...

THE GULF OF MEXICO...
WEAK SURFACE RIDGING EXTENDS ACROSS THE MAJORITY OF THE GULF OF
MEXICO EXTENDING FROM A SURFACE HIGH OVER GEORGIA TO THE SW
GULF. A FEW SHOWERS/THUNDERSTORMS CONTINUE OVER THE FAR NW GULF
N OF 27N BETWEEN 93W-96W DUE TO INCREASED RETURN FLOW AROUND THE
SURFACE RIDGE. THE SE GULF IS ALREADY BEING IMPACTED BY
LOW-LEVEL MOISTURE WRAPPING AROUND THE NORTHERN SIDE OF TROPICAL
STORM ISAAC WITH STRONG SHOWERS EXTENDING THROUGH THE FLORIDA
STRAITS AND PORTIONS OF SOUTH FLORIDA AS WELL AS CUBA. THIS
ACTIVITY IS ENHANCED BY DIFFLUENCE ALOFT AROUND AN UPPER LEVEL
TROUGH EXTENDING FROM THE FLORIDA PANHANDLE TO THE YUCATAN
PENINSULA. THIS UPPER TROUGH WILL PLAY A ROLE IN THE TRACK OF
ISAAC ONCE IT APPROACHES THE SE GULF. UPPER LEVEL RIDGING IS TO
EITHER SIDE OF THE TROUGH. DRY AIR ALOFT IS SINKING S AROUND THE
WEST SIDE OF THE UPPER TROUGH AND CONTINUING INTO THE NW
CARIBBEAN. THIS DRY AIR IS HELPING MAINTAIN MOSTLY CLEAR SKIES
FOR NOW. AS THE CENTER OF ISAAC MOVES CLOSER TO THE BASIN
TONIGHT CONDITIONS ACROSS THE SE GULF WILL BEGIN TO DETERIORATE
AND WILL CONTINUE THROUGH SUNDAY NIGHT AND INTO MONDAY
EVENTUALLY SPREADING NORTHWARD. INTERESTS IN THE EASTERN GULF OF
MEXICO SHOULD CONTINUE TO MONITOR THE PROGRESS OF TROPICAL STORM
ISAAC.

THE CARIBBEAN SEA...
TROPICAL STORM ISAAC IS DOMINATING THE CARIBBEAN PRODUCING
WIDESPREAD SHOWERS/THUNDERSTORMS ACROSS MUCH OF THE NORTHERN
CARIBBEAN ISLANDS ESPECIALLY HISPANIOLA AND PORTIONS OF CUBA.
REPORTS FROM HAITI ALREADY ARE INDICATING LARGE AREAS OF DAMAGE
AND FLOODING. REPORTS FROM CUBA ARE ALSO INDICATING COASTAL
FLOODING IS IN PORTIONS OF BARACOA...GIBARA...AND BANES.
FLOODING AND MUDSLIDES ARE LIKELY ACROSS BOTH HAITI AND PORTIONS
OF CUBA AS RAINFALL CONTINUES. THE ENTIRE CIRCULATION AROUND
ISAAC IS LARGE AND FAIRLY ELONGATED WITH A SURFACE TROUGH
EXTENDING FROM SW CUBA NEAR 20N77W THROUGH A WEAK SPOT LOW AT
19N81W TO 19N87W. SOME STRONGER SHOWERS/THUNDERSTORMS HAVE
RECENTLY POPPED UP NEAR THE CENTER OF ISAAC AND ACROSS EASTERN
CUBA TO JAMAICA. DUE TO THE LARGE CIRCULATION...MUCH OF THE
NORTHERN CARIBBEAN WITH CONTINUE TO SEE WIND AND RAIN AS THE
STORM CONTINUES TOWARDS THE GULF OF MEXICO. THE NW AND SW
CARIBBEAN ARE THE ONLY AREAS STILL UNDER MOSTLY FAIR CONDITIONS
DUE TO DRY AIR ALOFT SINKING INTO THE BASIN FROM THE CENTRAL
GULF OF MEXICO. SOME STRONG SHOWERS/THUNDERSTORMS HAVE ALSO
FORMED OVER COSTA RICA LIKELY INFLUENCED BY THE MONSOON TROUGH
EXTENDING FROM THE E PACIFIC TROUGH COSTA RICA AND PANAMA TO
NORTHERN COLUMBIA. ALL INTERESTS IN THE NORTHERN CARIBBEAN
SHOULD CONTINUE TO MONITOR ISAAC.

THE ATLANTIC OCEAN...
THE COMBINATION OF LOW-LEVEL MOISTURE BEING DRAWN ACROSS THE
BAHAMAS DUE TO TROPICAL STORM ISAAC AND DIFFLUENCE ALOFT AROUND
AN UPPER TROUGH OVER THE EASTERN GULF OF MEXICO IS HELPING
PRODUCE SCATTERED SHOWERS/THUNDERSTORMS ACROSS MUCH OF THE
BAHAMAS AND SOUTH FLORIDA S OF 26N W OF 67W. UPPER LEVEL
RIDGING...OUTFLOW FROM ISAAC COVERS THE MAJORITY OF THE WEST
ATLC. AN UPPER LEVEL LOW IS TO THE EAST NEAR 20N57W WITH AN
ELONGATED AXIS EXTENDING TO THE NW. IT IS HELPING PRODUCE
ISOLATED SHOWERS/THUNDERSTORMS FROM 20N-23N BETWEEN 58W-62W...AS
WELL AS FROM 23N-31N BETWEEN 54W-59W. SOME OF THIS ACTIVITY IS
ALSO INFLUENCED FROM A SURFACE TROUGH EXTENDING FROM 26N56W TO
20N52W. THIS SURFACE TROUGH IS THE REMNANTS OF JOYCE WHICH
DISSIPATED A FEW DAYS AGO. THE REMAINDER OF THE ATLC IS
DOMINATED BY BROAD SURFACE RIDGING AROUND A PAIR OF HIGH CENTERS
N OF THE AREA. THE RIDGE IS SUPPORTED BY A BROAD UPPER LEVEL
RIDGE CENTERED NEAR 31N46W WITH A SECOND UPPER RIDGE CENTERED
OVER WEST AFRICA. THE LAST VISIBLE SATELLITE IMAGES ALONG WITH
GOES-R ENHANCEMENT IMAGERY INDICATE AN AREA OF DUST EXTENDS
BETWEEN THE TROPICAL WAVE IN THE TROPICAL ATLC AND THE SURFACE
TROUGH IN THE CENTRAL ATLC. SOME DUST ALSO IS EMERGING OFF THE
COAST OF AFRICA BEHIND THE WAVE.

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

$$
WALTON





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