TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL  
805 PM EDT THU AUG 18 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2315 UTC.

...SPECIAL FEATURE...
THE TROPICAL WAVE IN THE W CARIBBEAN EXTENDS FROM 18N81W TO 
12N80W. A WELL DEFINED MID LEVEL CYCLONIC CIRCULATION IS ALONG 
THE WAVE AXIS NEAR 16N. SCATTERED MODERATE/ISOLATED STRONG 
CONVECTION IS FROM 14N-17N BETWEEN 78W-82W. A LOW LEVEL 
CIRCULATION IS BECOMING BETTER DEFINED AND A SURFACE LOW COULD 
BE FORMING ABOUT 90 NM ENE OF CAPE GRACIAS A DIOS NICARAGUA. 
ENVIRONMENTAL CONDITIONS REMAIN CONDUCIVE FOR A TROPICAL 
DEPRESSION TO FORM AS LONG AS THE DISTURBANCE REMAINS OFFSHORE. 
THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A TROPICAL CYCLONE 
BEFORE IT MOVES INLAND OVER CENTRAL AMERICA. TROPICAL STORM 
CONDITIONS ARE POSSIBLE ALONG THE COASTS OF HONDURAS...THE BAY 
ISLANDS...GUATEMALA AND BELIZE DURING THE NEXT DAY OR TWO AS THE 
SYSTEM MOVES GENERALLY WESTWARD AT 9-13 KT. 

A TROPICAL WAVE WAS INTRODUCED ON THE 18/1800 UTC MAP ALONG THE 
COAST OF W AFRICA NEAR 16W FROM 13N-21N. A BROAD MID LEVEL 
CYCLONIC CIRCULATION COVERS THE AREA FROM 8N-16N E OF 22W TO 
INLAND OVER W AFRICA. THIS WAVE IS ALREADY SHOWING SIGNS OF 
ORGANIZATION WITH A STRONG SURFACE CYCLONIC CIRCULATION 
DEVELOPING ON THE SOUTHERN EXTENT OF THIS TROPICAL WAVE. 
SCATTERED/NUMEROUS STRONG CONVECTION IS WITHIN 75 NM ALONG A 
LINE FROM 12N19W 14N19W TO INLAND OVER SENEGAL NEAR DAKAR. 
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVER 
THE AREA FROM 8N-13N BETWEEN 17W-25W. UPPER LEVEL WINDS ARE 
FORECAST TO BE CONDUCIVE FOR FURTHER DEVELOPMENT DURING THE NEXT 
COUPLE OF DAYS. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A 
TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES 
WEST-NORTHWESTWARD AT 10 TO 15 MPH.  REGARDLESS OF 
DEVELOPMENT...LOCALLY HEAVY RAIN AND STRONG GUSTY WINDS ARE 
POSSIBLE IN THE CAPE VERDE ISLANDS FRIDAY INTO SATURDAY.   

...TROPICAL WAVES...

TROPICAL WAVE IN THE CENTRAL TROPICAL ATLC EXTEND FROM 19N43W 
ALONG 15N43W TO JUST N OF THE MONSOON TROUGH NEAR 13N41W MOVING 
W 15-20 KT. THIS WAVE IS WELL DEFINED IN THE LOWER LEVELS 
COVERING A BROAD AREA AND BECOMING TILTED NW/SE. WAVE REMAINS 
EMBEDDED WITHIN A SURGE OF DEEP LAYER MOISTURE. SCATTERED 
SHOWERS ARE FROM 13N-17N BETWEEN 40W-46W. 

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

THE DEPICTION ON THE SURFACE ANALYSIS HAS A SPLIT MONSOON TROUGH 
ALONG 16W AS A RESULT OF A VERY ACTIVE TROPICAL WAVE MOVING OFF 
THE COAST OF AFRICA...SEE SPECIAL FEATURES ABOVE. ONE PORTION OF 
THE MONSOON TROUGH EXTENDS ACROSS AFRICA. THE OTHER PORTION OF 
THE MONSOON TROUGH EXTENDS FROM A DEVELOPING CIRCULATION 
ASSOCIATED WITH THIS TROPICAL WAVE INTO THE TROPICAL ATLC NEAR 
13N17W ALONG 15N31W RUNNING JUST S OF THE TROPICAL WAVE NEAR 
12N41W TO 9N48W. THE ITCZ AXIS CONTINUES FROM 9N48W ALONG 10N55W 
TO SOUTH AMERICA NEAR 10N62W. SCATTERED MODERATE/ISOLATED STRONG 
CONVECTION IS WITHIN 150 NM S OF THE MONSOON TROUGH BETWEEN 
43W-48W. SMALL CLUSTERS OF SCATTERED MODERATE CONVECTION DOT THE 
AREA FROM 5N-10N BETWEEN 25W-37W. 

...DISCUSSION...

GULF OF MEXICO...
BROAD UPPER RIDGE DOMINATES THE GULF N OF 24N ANCHORED OVER 
CENTRAL TEXAS. AN INVERTED UPPER TROUGH IS OVER THE BAY OF 
CAMPECHE EXTENDING FROM THE ISTHMUS OF TEHUANTEPEC TO THE N 
COAST OF THE YUCATAN PENINSULA NEAR MERIDA GENERATING SCATTERED 
SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS INLAND ALONG THE 
COAST OF MEXICO. UPPER LEVEL CONVERGENCE IS GENERATING SCATTERED 
SHOWERS/ISOLATED THUNDERSTORMS OVER THE W GULF FROM 24N-26N 
BETWEEN 92W-96W. A SURFACE TROUGH EXTENDS FROM S GEORGIA THEN 
INTO THE GULF NEAR TALLAHASSEE ALONG 27N85W 24N88W TO 24N92W. 
AFTERNOON SHOWERS/THUNDERSTORMS HAVE DEVELOPED INLAND OVER THE 
FLORIDA PENINSULA AND SE LOUISIANA WITH SOME ISOLATED SHOWERS 
MOVING TO ALONG THE IMMEDIATE COASTLINES AND OVER THE FLORIDA 
KEYS. THIS SURFACE TROUGH EFFECTIVELY SPLITS THE SURFACE RIDGE 
FROM THE W ATLC WITH A 1016 MB HIGH OVER THE W GULF NEAR 27N95W. 
WEAK SURFACE RIDGE WILL PREVAIL OVER THE N GULF THROUGH MON. A 
TROPICAL WAVE IS EXPECTED TO MOVE ACROSS THE BAY OF CAMPECHE SUN 
AND MON.

CARIBBEAN SEA...
THE PRIMARY CONCERN THIS EVENING IS THE POTENTIAL FOR TROPICAL 
FORMATION ASSOCIATED WITH THE TROPICAL WAVE IN THE W 
CARIBBEAN...SEE SPECIAL FEATURES ABOVE. THIS FEATURE IS 
DOMINATING THE CARIBBEAN AND IS GENERATING ADDITIONAL SCATTERED 
SHOWERS/ISOLATED THUNDERSTORMS COVERING THE AREA BETWEEN 
75W-86W. AN UPPER LEVEL RIDGE COVERS THE CARIBBEAN W OF 73W 
ANCHORED NEAR THE CAYMAN ISLANDS. A LARGE UPPER TROUGH IN THE 
CENTRAL ATLC EXTENDS S OVER THE NE CARIBBEAN GENERATING 
SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS FROM N OF 
15N BETWEEN 70W-75W LEAVING THE REMAINDER OF THE CARIBBEAN UNDER 
MOSTLY CLEAR SKIES THIS EVENING. A SURFACE LOW IS EXPECTED TO 
DEVELOP ALONG THE CARIBBEAN TROPICAL WAVE WITH THE POSSIBILITY 
OF TROPICAL CYCLONE FORMATION...SEE SPECIAL FEATURES ABOVE. THE 
LOW WILL THEN MOVE W THROUGH THE GULF OF HONDURAS FRI AFTERNOON 
TO INLAND OVER BELIZE SAT NIGHT. A TROPICAL WAVE IN THE CENTRAL 
ATLC WILL ENTER THE NE CARIBBEAN SUN TO THE CENTRAL CARIBBEAN ON 
TUE.

ATLANTIC OCEAN...
A SHORTWAVE UPPER TROUGH EXTENDS ALONG THE CAROLINA COAST INTO 
THE W ATLC THEN THROUGH 32N78W TO NEAR GRAND BAHAMA ISLAND 
GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS WITHIN 120 
NM OF LINE FROM OVER W CUBA NEAR SANTA CLARA ACROSS THE BAHAMAS 
TO NEAR 32N74W. A LARGE UPPER LEVEL TROUGH COVERS THE REMAINDER 
OF THE W ATLC AND INTO THE CENTRAL ATLC EXTENDING FROM BEYOND 
32N55W THEN THROUGH AN UPPER LOW NEAR 26N57W ACROSS HISPANIOLA/ 
PUERTO RICO INTO THE NE CARIBBEAN. SCATTERED SHOWERS AND 
POSSIBLE ISOLATED THUNDERSTORMS ARE WITHIN 120 NM OF LINE FROM 
27N60W TO 32N55W. LOW LEVEL SPEED CONVERGENCE AND AN ABUNDANCE 
OF DEEP LAYER MOISTURE IS GENERATING SCATTERED SHOWERS AND 
POSSIBLE ISOLATED THUNDERSTORMS E OF THE LESSER ANTILLES FROM 
11N-15N BETWEEN 57W AND THE LESSER ANTILLES. THE REMAINDER OF 
THE ATLC BASIN IS DOMINATED BY A SURFACE RIDGE THAT EXTENDS FROM 
A 1025 MB HIGH OVER THE AZORES THROUGH A 1022 MB HIGH NEAR 
33N59W TO THE FLORIDA COAST NEAR DAYTONA BEACH LEAVING THE 
REMAINDER OF THE ATLC UNDER FAIR CONDITIONS THIS EVENING. TWO 
AREAS OF SAHARAN DRY AIR ARE ACROSS THE ATLC BASIN. THE LARGEST 
S ACROSS THE TROPICAL ATLC FROM 15N-30N E OF 57W. THE SECOND IS 
SMALLER N OF THE E CARIBBEAN FROM 20N-28N BETWEEN 63W-70W. THE W 
ATLC SURFACE RIDGE WILL GRADUALLY WEAKEN SAT THROUGH MON.