000
AXNT20 KNHC 190002
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL  
805 PM EDT SUN SEP 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...

A 1009 MB LOW IS EMBEDDED ON THE MONSOON TROUGH NEAR 12N36W. 
THIS LOW HAS BECOME BETTER DEFINED DURING THE PAST SEVERAL 
HOURS. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR GRADUAL 
DEVELOPMENT OF THIS DISTURBANCE OVER THE NEXT FEW DAYS AS IT 
MOVES SLOWLY WESTWARD. THIS SYSTEM HAS A CHANCE OF BECOMING A 
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST OF GUINEA 
BISSAU NEAR 12N16W TO A 1011 MB LOW NEAR 10N25W TO A SECOND 1009 
MB LOW NEAR 12N36W TO 10N40W TO 9N49W. THE MONSOON TROUGH HAS 
BECOME THE DOMINANT FEATURE ACROSS THE TROPICAL ATLC WITH NO 
INTER-TROPICAL CONVERGENCE ZONE. SCATTERED MODERATE CONVECTION 
IS FROM 9N-12N BETWEEN 16W-18W. WIDELY SCATTERED MODERATE 
CONVECTION IS FROM 4N-9N BETWEEN 18W-30W...FROM 6N-13N BETWEEN 
30W-40W...AND FROM 5N-10N BETWEEN 40W-50W.

...DISCUSSION...

GULF OF MEXICO...
RADAR IMAGERY SHOWS SCATTERED SHOWERS AND RAIN ALONG THE COASTS 
OF TEXAS AND LOUISIANA MOVING E. MOST OF THE PRECIPITATION IS N 
OF 28N BETWEEN 88W-96W. ELSEWHERE ISOLATED SHOWERS ARE OVER S 
FLORIDA S OF LAKE OKEECHOBEE. A SURFACE TROUGH IS INLAND OVER S 
MEXICO AND THE YUCATAN PENINSULA FROM 21N89W TO 15N93W. WIDELY 
SCATTERED MODERATE CONVECTION IS WITHIN 120 NM OF THE TROUGH. 
SURFACE RIDGING DOMINATES THE GULF OF MEXICO WITH 10-15 KT E-SE 
WINDS. MOSTLY FAIR WEATHER IS OVER THE REMAINDER OF THE GULF. 
EXPECT THE SURFACE TROUGH TO ADVECT CONVECTION OVER THE SOUTH 
CENTRAL GULF AND THE BAY OF CAMPECHE OVER THE NEXT 24 HOURS. 
ALSO EXPECT MORE SHOWERS OVER THE N GULF COAST FROM TEXAS TO 
FLORIDA OVER THE NEXT 24 HOURS.     

CARIBBEAN SEA...
A SURFACE TROUGH IS ALONG THE COAST OF NICARAGUA FROM 15N83W TO 
10N84W. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS FROM 
8N-14N BETWEEN 80W-84W TO INCLUDE PORTIONS OF THE SW GULF. 
ANOTHER SURFACE TROUGH IS OVER THE E CARIBBEAN FROM 20N66W TO 
14N67W. WIDELY SCATTERED MODERATE CONVECTION IS E OF THE TROUGH 
AXIS FROM 14N-20N BETWEEN 61W-66W TO INCLUDE PUERTO RICO AND THE 
LEEWARD ISLANDS. THE MONSOON TROUGH EXTENDS FROM N COLOMBIA TO S 
COSTA RICA. SCATTERED MODERATE CONVECTION IS FROM 7N-10N BETWEEN 
77W-84W. 10-20 KT TRADEWINDS ARE OVER THE CARIBBEAN WITH 
STRONGEST WINDS ALONG THE COAST OF N COLOMBIA. EXPECT THE 
SURFACE TROUGHS TO DRIFT W OVER THE NEXT 24 HOURS WITH 
CONVECTION. ALSO EXPECT CONTINUED CONVECTION OVER THE SW 
CARIBBEAN DUE TO THE MONSOON TROUGH. 

ATLANTIC OCEAN...
A DISSIPATING STATIONARY FRONT IS OFF THE COAST OF N FLORIDA 
FROM 29N-31N BETWEEN 79W-81W. A SURFACE TROUGH IS OVER THE W 
ATLANTIC FROM THE BAHAMAS AT 28N76W TO E CUBA AT 22N78W. 
SCATTERED SHOWERS ARE WITHIN 120 NM OF THE TROUGH AXIS. A 
SURFACE TROUGH IS OVER THE CENTRAL ATLANTIC FROM 32N37W TO 
27N41W. SCATTERED MODERATE CONVECTION IS E OF THE TROUGH AXIS 
FROM 28N-31N BETWEEN 34W-37W. A 1010 MB LOW IS OVER THE CENTRAL 
TROPICAL ATLANTIC NEAR 17N45W. A SURFACE TROUGH EXTENDS N FROM 
THE LOW TO 21N43W. ISOLATED MODERATE CONVECTION IS FROM 18N-20N 
BETWEEN 40W-44W. 

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

$$

FORMOSA