[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171749
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED AUG 17 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 1715 UTC.

...SPECIAL FEATURE...
AN ACTIVE TROPICAL WAVE IS MOVING THROUGH THE CENTRAL CARIBBEAN
EXTENDING S OF HAITI ALONG 18N72W TO 12N74W MOVING W NEAR 20 KT.
SATELLITE IMAGERY INDICATES A CLEAR MID-LEVEL CIRCULATION AROUND
THE AXIS NEAR 15N...BUT A WELL-DEFINED SURFACE CIRCULATION HAS
NOT FORMED AT THIS TIME. ENHANCED DEEP LAYER MOISTURE
ACCOMPANIES THE WAVE BETWEEN 71W-77W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 13N-18N BETWEEN
72W-78W. A SMALL CLUSTER OF SIMILAR ACTIVITY IS S OF THE
DOMINICAN REPUBLIC FROM 17N-18N BETWEEN 70W-71W. SOME GRADUAL
DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER THE NEXT COUPLE OF
DAYS.


...TROPICAL WAVES...

WELL DEFINED TROPICAL WAVE IS ACROSS THE ERN TRPCL ATLC ALONG
19N33W TO THE MONSOON TROUGH NEAR 13N33W MOVING W 15-20 KT.
SATELLITE IMAGERY SHOWS DISTINGUISHABLE LOW-LEVEL CYCLONIC FLOW
AROUND THE WAVE AXIS CONCENTRATED AT THE INTERSECTION WITH THE
MONSOON TROUGH. THIS CYCLONIC FLOW IS ALSO EVIDENT IN
SCATTEROMETER DATA. THE WAVE IS EMBEDDED WITHIN A SURGE OF DEEP
LAYER MOISTURE EXTENDING TO 20N. ISOLATED MODERATE CONVECTION IS
W OF THE WAVE AXIS FROM 12N-15N BETWEEN 35W-37W.

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

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 20N16W
ALONG 16N24W TO S OF A TROPICAL WAVE NEAR 13N33W TO 9N41W. THE
ITCZ CONTINUES FROM 9N41W TO 5N54W. SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS FROM 8N-14N BETWEEN 13W-21W. SIMILAR
ACTIVITY IS FROM 6N-9N BETWEEN 34W-40W.

...DISCUSSION...

THE GULF OF MEXICO...
A LONGWAVE UPPER LEVEL TROUGH NOW OVER THE FAR WRN ATLC
CONTINUES TO SUPPORT A WEAK STATIONARY FRONT IN THE NE GULF OF
MEXICO EXTENDING FROM THE BIG BEND OF FLORIDA NEAR 29N83W ALONG
27N87W TO SE LOUISIANA NEAR 30N90W. A SURFACE TROUGH IS S OF THE
FRONT ALONG 27N83W TO 25N87W. SCATTERED SHOWERS/THUNDERSTORMS
ARE WITHIN 60 NM EITHER SIDE OF THE TROUGH AXIS. SIGNIFICANT DRY
AIR ALOFT EXTENDS N OF THE FRONT KEEPING CONDITIONS FAIR. THE
REMAINDER OF THE BASIN IS ALSO UNDER MOSTLY FAIR WEATHER
INFLUENCED BY WEAK SURFACE RIDGING AROUND A 1017 MB HIGH IN THE
NW GULF NEAR 27N92W. ALOFT...MAINLY DRY ALOFT COVERS THE BASIN
IN NELY FLOW AROUND AN UPPER LEVEL RIDGE CENTERED OVER NEW
MEXICO. EXPECT WEAK RIDGING TO REMAIN OVER THE WRN HALF OF THE
BASIN WITH THE STATIONARY FRONT CONTINUING TO SIT OVER THE NE
GULF.

THE CARIBBEAN SEA...
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE ACROSS THE NW
CARIBBEAN NEAR A SURFACE TROUGH EXTENDING FROM S OF WRN CUBA
NEAR 22N82W TO 19N86W. THE TROUGH IS SUPPORTED BY A NARROW UPPER
LEVEL TROUGH EXTENDING FROM WRN CUBA TO GUATEMALA. AN ACTIVE
TROPICAL WAVE IS S OF HAITI SUPPORTING SHOWERS/THUNDERSTORMS
FROM 13N-18N BETWEEN 72W-78W. SEE SPECIAL FEATURES SECTION FOR
MORE DETAILS. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO IN THE SW
CARIBBEAN FROM 10N-12N BETWEEN 79W-85W ASSOCIATED WITH THE
MONSOON TROUGH THAT EXTENDS JUST S OF COSTA RICA AND PANAMA. THE
ERN CARIBBEAN IS EXPERIENCING MOSTLY FAIR CONDITIONS WITH A FEW
AREAS OF SHOWERS EMBEDDED WITHIN THE TRADEWIND FLOW FROM 13N-14N
BETWEEN 62W-70W...AND FROM 16N-18N BETWEEN 63W-65W. ALOFT...AN
UPPER LEVEL INVERTED TROUGH IS OVER THE SW CARIBBEAN WHILE
MOSTLY ELY FLOW ALOFT COVERS THE ERN AND CENTRAL CARIBBEAN.
EXPECT THE TROPICAL WAVE IN THE CENTRAL CARIBBEAN TO MOVE WWD.
AN AREA OF MOISTURE JUST E OF THE LESSER ANTILLES IS CURRENTLY
PRODUCING SCATTERED SHOWERS/THUNDERSTORMS. THIS AREA OF MOISTURE
MAY BEGIN TO IMPACT THE ISLANDS DURING THE NEXT 24 HOURS AS THE
MOISTURE MOVES W.

THE ATLANTIC OCEAN...
A LARGE AREA OF SHOWERS/THUNDERSTORMS IS OVER THE WRN ATLC
ASSOCIATED WITH A DEEP LAYER TROUGH EXTENDING DOWN 77W. THE
UPPER TROUGH SUPPORTS A STATIONARY FRONT ALONG 31N77W TO THE BIG
BEND OF FLORIDA NEAR 29N83W. SCATTERED SHOWERS/THUNDERSTORMS ARE
S OF THE BOUNDARY FROM 28N-32N BETWEEN 63W-79W. ISOLATED
ACTIVITY IS OVER THE WRN BAHAMAS. AN UPPER LEVEL LOW IS NE OF
THE LEEWARD ISLANDS CENTERED NEAR 24N56W SUPPORTING ISOLATED
SHOWERS FROM 22N-23N BETWEEN 54W-57W...AND FROM 18N-20N BETWEEN
56W-63W. AN AREA OF SHOWERS/THUNDERSTORMS IS ALSO TO THE S AND E
OF THE LEEWARD ISLANDS FROM 9N-16N BETWEEN 53W-59W ASSOCIATED
WITH AN AREA OF ENHANCED MOISTURE EVIDENT IN TOTAL PRECIPITABLE
WATER IMAGERY. THE REMAINDER OF THE BASIN IS DOMINATED BY
SURFACE RIDGING AROUND A 1025 MB HIGH NEAR 32N55W AND A 1024 MB
HIGH NEAR 33N33W PROVIDING MOSTLY FAIR WEATHER. ALOFT...TO THE
N...AN UPPER LEVEL RIDGE IS CENTERED NEAR 39N41W. A SECOND UPPER
RIDGE IS OVER THE W TROPICAL ATLC NEAR 17N50W. A BROAD UPPER
RIDGE COVERS THE ERN ATLC CENTERED S OF THE CANARY ISLANDS WITH
AXIS ALONG 25N. AN UPPER LEVEL TROUGH IS TO THE N OF 30N WITH
AXIS ALONG 19W. VISIBLE SATELLITE IMAGERY CONTINUES TO SHOW TWO
AREAS OF AFRICAN DUST. THE FIRST IS E OF 45W WITH CLEARING
AROUND THE TROPICAL WAVE ALONG 33W. THE SECOND AREA IS N OF THE
CARIBBEAN BETWEEN 55W-75W.

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

$$
WALTON





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