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000
AXNT20 KNHC 212344
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE MAY 21 2013

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.

...TROPICAL WAVES...
TROPICAL WAVE EXTENDS FROM 7N36W TO EQ39W THROUGH A 1011 MB
SURFACE LOW NEAR 4N38W MOVING WEST NEAR 10 KT. THIS POSITION IS
SLIGHTLY EAST OF THE LAST ANALYSIS. THIS WAS DONE DUE TO MORE
PROMINENT LOW LEVEL CYCLONIC FLOW NEAR THE WEAK SURFACE
LOW...AND WAS ALSO EVIDENT IN 1000 MB STREAMLINES IN MODEL
GUIDANCE. THERE ARE SEVERAL PIECES OF ENERGY IN THE VICINITY AND
IT IS HARD TO DETERMINE WHICH WILL BECOME DOMINANT...AS IS
COMMON THIS TIME OF YEAR. A CLUSTER OF MODERATE/STRONG
CONVECTION IS NEAR THE LOW CENTER.

TROPICAL WAVE MOVES THROUGH THE EASTERN CARIBBEAN ALONG 17N68W
TO 10N71W MOVING WEST NEAR 15 KT. THE WAVE COINCIDES WITH A
BROAD AREA OF INCREASED MOISTURE EVIDENT IN TOTAL PRECIPITABLE
WATER IMAGERY. DUE TO UPPER LEVEL WESTERLY FLOW...SOME OF THE
MOISTURE IS BEING DRAWN EASTWARD ACROSS THE NE CARIBBEAN
INCLUDING THE LEEWARD ISLANDS. SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS ARE NORTH OF 14N EAST OF 70W.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM THE COAST OF GUINEA NEAR 10N13W
TO 7N18W. THE ITCZ BEGINS AT 7N18W AND CONTINUES ALONG 4N26W
5N36W. ISOLATED MODERATE CONVECTION IS FROM 2N-6N BETWEEN 14W-
20W. SIMILAR ACTIVITY IS FROM 3N-6N BETWEEN 23W-34W.

...DISCUSSION...

GULF OF MEXICO...
MOSTLY CLEAR SKIES SPREAD THROUGHOUT THE GULF OF MEXICO
ASSOCIATED WITH DRY AIR ALOFT AROUND A BROAD UPPER LEVEL RIDGE
COVERING THE BASIN ALONG 90W. THE UPPER RIDGE SUPPORTS BROAD
SURFACE RIDGING EXTENDING FROM THE WEST ATLC. HOWEVER...A
SHORTWAVE UPPER LEVEL TROUGH LIES ACROSS FLORIDA ALONG 80W/81W
PROVIDING DIFFLUENCE ALOFT. THIS PATTERN COMBINED WITH DIURNAL
HEATING HAS LED TO HEAVY SHOWERS AND THUNDERSTORMS ACROSS MUCH
OF THE FLORIDA PENINSULA. RADAR IMAGERY INDICATES THE ACTIVITY
IS MAINLY CONCENTRATED ALONG THE WEST COAST OF FLORIDA AND
ACROSS THE SOUTH CENTRAL PORTIONS NEAR LAKE OKEECHOBEE. EAST TO
SOUTHEAST SURFACE WINDS DOMINATE THE AREA RANGING FROM 10 KT IN
THE EASTERN GULF TO 15-20 IN THE WESTERN GULF. SURFACE RIDGING
WILL REMAIN DOMINANT AT THE SURFACE FOR THE NEXT SEVERAL DAYS.
THE UPPER TROUGH OVER FLORIDA SHOULD DRIFT EAST OF FLORIDA IN
THE NEXT 24 HOURS...BUT IT MAY STILL INFLUENCE AFTERNOON
CONVECTIVE ACTIVITY TOMORROW.

CARIBBEAN SEA...
UPPER LEVEL RIDGING ALONG WITH DRY AIR ALOFT SPREADS INTO THE NW
CARIBBEAN FROM THE GULF OF MEXICO PROVIDING CLEAR SKIES AND
FAIR WEATHER. HEAVY SHOWERS AND SCATTERED THUNDERSTORMS ARE
ACROSS THE SW CARIBBEAN ASSOCIATED WITH THE MONSOON TROUGH THAT
EXTENDS FROM COSTA RICA ALONG 10N TO NORTHERN COLOMBIA. A WEAK
1009 MB SURFACE LOW IS ANALYZED ALONG THE MONSOON TROUGH NEAR
10N79W. ACTIVITY IS MAINLY SOUTH OF 12N. IT IS ALSO ENHANCED BY
DIFFLUENT FLOW ALOFT AS MOIST SOUTHWESTERLY FLOW ALOFT IS
PRESENT TO THE EAST AND ACROSS THE REMAINDER OF THE BASIN. THE
SOUTHWEST FLOW ALOFT IS SHEARING MOISTURE NEAR A TROPICAL WAVE
IN THE EASTERN CARIBBEAN NEAR 70W AND DRAWING IT ACROSS THE NE
CARIBBEAN. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE
NORTH OF 14N EAST OF 70W. AFTERNOON CONVECTIVE SHOWERS AND
THUNDERSTORMS ARE ALSO COVERING MUCH OF
CUBA...HISPANIOLA...JAMAICA...AND PUERTO RICO. TRADEWIND FLOW OF
15-20 KT IS PRESENT THROUGHOUT MUCH OF THE AREA. THE WAVE IS
EXPECTED TO CONTINUE MOVING WEST AND WILL LIKELY MERGE WITH THE
MOISTURE FIELD NEAR THE MONSOON TROUGH IN THE SW CARIBBEAN.

HISPANIOLA...
AFTERNOON CONVECTION ACTIVITY IS BEGINNING TO DIE DOWN ACROSS
HISPANIOLA WITH A FEW THUNDERSTORMS STILL PRESENT OVER HAITI
WITH SHOWERS CONTINUING OVER THE CENTRAL PORTION OF THE ISLAND.
TOTAL PRECIPITABLE WATER IMAGERY INDICATES THAT AN INCREASED
AREA OF MOISTURE IS APPROACHING THE ISLANDS FROM THE EAST
ASSOCIATED WITH A TROPICAL WAVE TO THE SOUTH. THIS LOW-LEVEL
MOISTURE COMBINED WITH UPPER LEVEL MOISTURE STREAMING EASTWARD
FROM A SHORTWAVE TROUGH NEAR FLORIDA WILL PROVIDE AN INCREASED
CHANCE FOR HEAVIER THAN NORMAL AFTERNOON CONVECTION TOMORROW.

ATLANTIC OCEAN...
A SHORTWAVE UPPER TROUGH IS JUST EAST OF FLORIDA NEAR 80W
PROVIDING DIFFLUENCE ALOFT ACROSS THE BAHAMAS. SCATTERED SHOWERS
AND THUNDERSTORMS ARE MAINLY FROM 23N-28N BETWEEN 75W-79W WITH
ACTIVITY CONTINUING OVER CUBA. UPPER LEVEL RIDGING COVERS THE
REMAINDER OF THE WEST ATLC SUPPORTING SURFACE RIDGING AROUND A
1024 MB HIGH NEAR 31N58W. A NARROW UPPER TROUGH NEAR 44W
SUPPORTS A COLD FRONT THAT ENTERS THE AREA NEAR 32N44W AND
CONTINUES TO 27N51W WHERE IT BEGINS TO DISSIPATE TO NEAR 26N59W.
SCATTERED SHOWERS ARE NORTH OF 30N BETWEEN 41W-47W. A WEAK 1019
MB SURFACE LOW IS SOUTH OF THE FRONT NEAR 27N48W WITH A SURFACE
TROUGH EXTENDING THROUGH IT ALONG 29N47W TO 23N50W. NO SHOWER
ACTIVITY IS NEAR THE TROUGH/LOW. THE REMAINDER OF THE EAST ATLC
IS DOMINATED BY SURFACE RIDGING CENTERED WELL NORTH OF THE AREA.
THE RIDGE IS SUPPORTED BY AN UPPER LEVEL RIDGE CENTERED NEAR
44N27W. BROAD UPPER RIDGING ALSO COVERS THE TROPICAL ATLC.

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

$$
WALTON