000
AXNT20 KNHC 211753
TWDAT 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE APR 21 2009

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...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
XXXX UTC.

...THE ITCZ... 
ITCZ AXIS IS CENTERED ALONG 06N10W 02.5N20W CROSSING THE EQUATOR 
NEAR 24W TO 02S30W TO NE BRAZIL NEAR 03S40W. CONVECTION HAS 
INCREASED IN AREAL EXTENT NEAR THE ITCZ IN THE LAST 24 HOURS. 
SCATTERED MODERATE TO STRONG CONVECTION IS WITHIN 150 NM N OF 
THE ITCZ AXIS WEST OF 19W AND WITHIN 200 NM S OF THE AXIS WEST 
OF 19W.

...DISCUSSION...

THE GULF OF MEXICO...
A VERY LARGE DEEP LAYER TROUGH IS OVER THE EAST UNITED STATES 
AND EXTENDS SOUTH OVER THE AREA. AN ASSOCIATED COLD FRONT IS 
OVER THE STRAITS OF FLORIDA AND THE YUCATAN CHANNEL. A FEW 
SHOWERS REMAIN NEAR THIS FEATURE BUT MOST OF THE CONVECTION HAS 
MOVED EAST OF THE GULF OF MEXICO REGION. 
SURFACE HIGH PRESSURE OVER THE WEST GULF WILL SLOWLY MOVE EAST 
ACROSS THE AREA DURING THE NEXT 48 HOURS LEAVING A RIDGE OVER 
THE AREA. ATMOSPHERIC SUBSIDENCE NEAR THIS HIGH IS BEING 
SUPPORTED BY DRY NORTHWESTERLY FLOW ALOFT...AND WILL RESULT IN 
GENERALLY FAIR WEATHER CONDITIONS ACROSS THE ENTIRE GULF WITH 
RELATIVELY LIGHT SURFACE WINDS. AFTER THE SURFACE HIGH MOVES E 
OF THE GULF BY LATE WEEK...SE RETURN FLOW WILL BEGIN.

THE CARIBBEAN SEA... 
AN AREA OF CONVECTIVE ACTIVITY IS OVER THE SOUTHWEST CARIBBEAN 
AND IS ENHANCED BY LIFT FROM THE UPPER TROUGH MENTIONED IN THE 
GULF SECTION THAT EXTENDS SOUTH TO NEAR 10N. SURFACE SHIP AND 
BUOY OBSERVATION REVEALED 20-25 KT NE/E WINDS BETWEEN THE COAST 
OF COLOMBIA AND HISPANIOLA WITH 15-20 KT TRADES ELSEWHERE E OF 
80W. WINDS ARE LIGHT AND VARIABLE OVER THE W PORTION DUE TO THE 
PRESENCE OF A WEAK PREFRONTAL TROUGH ALONG 83W/84W. SOME 
MOISTURE...LIKELY CONTAINING ONLY ISOLATED SHOWERS AND 
TSTMS...HAS MOVED INTO THE NW CARIBBEAN AHEAD OF A COLD FRONT 
OVER THE YUCATAN CHANNEL. THIS FRONT IS EXPECTED TO MOVE 
INTO A PORTION OF THE AREA BUT SHOULD HAVE LITTLE SIGNIFICANT 
WEATHER IMPACTS.   

THE ATLANTIC OCEAN...
SCATTERED SHOWERS AND TSTMS ARE WITHIN 300 NM E OF THE COLD 
FRONT THAT EXTENDS THROUGH 32N77W TO SOUTH FLORIDA AND THE 
STRAITS OF FLORIDA ENHANCED BY UPPER DIFFLUENT FLOW AND LIFT 
ALONG THE COLD FRONT. SLY WINDS HAVE INCREASED TO 20-30 KT NEAR 
THE N BORDER W OF 72W DUE TO THE TIGHT PRESSURE GRADIENT BETWEEN 
THE FRONT AND A RIDGE THAT EXTENDS OVER THE AREA. OVER THE 
CENTRAL ATLC...DEEP LAYER TROUGHING REMAINS WELL DEFINED 
PROVIDING LIMITED SUPPORT FOR THE STATIONARY FRONT THAT WAS OVER 
THE AREA AND IS NOW CONSIDERED A TROUGH THROUGH 32N44W TO A WEAK 
SMALL SCALE LOW NEAR 26N57W. LITTLE WEATHER IS ASSOCIATED WITH 
THIS FEATURE. A MORE AMPLIFIED TROUGH...SUPPORTING ANOTHER 
FRONT...IS EXPECTED TO SWEEP SE AND ABSORB OR MERGE WITH THE 
WEAK LOW/TROUGH OVER THE NEXT COUPLE OF DAYS. A NARROW SWATH OF 
SCATTERED SHOWERS AND TSTMS ARE LOCATED IN THE UPPER DIFFLUENT 
ZONE N OF 22N BETWEEN 30W-40W. AN UPPER JET EXTENDING E-NE FROM 
NORTHERN COLOMBIA ACROSS THE SOUTHERN CARIBBEAN TO THE WINDWARD 
ISLANDS TO 18N30W WITH SOME HIGH CLOUDS IN A 120 NM WIDE BAND 
CENTERED ON THE JET. OTHERWISE...THE E ATLC IS DOMINATED BY A 
STRONG AZORES HIGH.  

$$
LL