000 AXNT20 KNHC 202344 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT FRI APR 20 2012 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. ...THE ITCZ/THE MONSOON TROUGH... THE MONSOON TROUGH EXTENDS INLAND ACROSS THE TROPICAL REGIONS OF WEST AFRICA INTO THE ATLC BASIN ACROSS THE COAST OF LIBERIA NEAR 6N11W TO 2N14W...WHERE THE ITCZ AXIS CONTINUES ALONG 1S30W TO THE COAST OF BRAZIL NEAR 3S40W. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS NOTED FROM THE EQUATOR TO 5N BETWEEN THE PRIME MERIDIAN AND 18W. SCATTERED MODERATE CONVECTION IS S OF 4N BETWEEN 20W AND 30W. ...DISCUSSION... GULF OF MEXICO... SHOWERS AND TSTMS ARE FLARED UP OVER FLORIDA AND THE EASTERN PORTION OF THE GULF AHEAD OF A SURFACE TROUGH EXTENDING FROM 27N85W TO 21N88W. A DIFFLUENT PATTERN ALOFT IS HELPING TO INDUCE THIS CONVECTIVE ACTIVITY. AS AN UPPER LEVEL TROUGH DEEPENS OVER THE CENTRAL PLAINS AND THE GULF OF MEXICO...EXPECT MORE SHOWERS AND TSTMS TO DEVELOP OVER THE EASTERN GULF AND PARTS OF FLORIDA THIS SATURDAY. SOME OF THESE TSTMS COULD BE STRONG OR SEVERE. A COLD FRONT IS REACHING THE COAST OF TEXAS. A BAND OF SHOWERS AND TSTMS IS JUST AHEAD OF THE FRONT AND IS PRESENTLY AFFECTING THE NW GULF WATERS STRETCHING FROM THE TEXAS/LOUISIANA BORDER TO BROWNSVILLE TEXAS. THE COLD FRONT IS EXPECTED TO ENTER THE GULF WATERS THIS EVENING REACHING A POSITION FROM THE MISSISSIPPI DELTA TO THE BAY OF CAMPECHE EARLY SAT AND FROM THE FLORIDA BIG BEND TO YUCATAN PENINSULA EARLY SUN. A FRONTAL WAVE OR WEAK LOW WILL DEVELOP ALONG THE FRONTAL BOUNDARY NEAR SE LOUISIANA ON SAT. THE LOW PRES WILL MOVE EWD ACROSS THE NORTHERN GULF WATERS INTO N FLORIDA SUN MORNING WHILE DEEPENING...THEN WILL CONTINUE NE ALONG THE SE U.S. COAST SUNDAY AFTERNOON. AS THE LOW PRES RACES NE LATE SAT NIGHT INTO EARLY SUN...THE COLD FRONT WILL MOVE RAPIDLY SE THROUGH THE STRAITS OF FLORIDA LATE SUN. FRESH TO STRONG WINDS OF 25-30 KT AND BUILDING SEAS OF UP TO 13 FT ARE EXPECTED IN THE WAKE OF THE FRONT. STRONG TO SEVERE TSTMS ARE ALSO POSSIBLE OVER PARTS OF FLORIDA WITH THE FRONTAL PASSAGE. THE AFOREMENTIONED DEEPENING UPPER-LEVEL TROUGH SUPPORTS THE EVOLUTION OF THIS WEATHER PATTERN. CARIBBEAN SEA... HIGH PRES LOCATED N OF AREA IS PRODUCING MODERATE TO FRESH NE TO E WINDS ACROSS THE BASIN. THE MOST RECENT SCATTEROMETER DATA CONFIRMED THE PRESENCE OF THESE WIND SPEEDS. SCATTERED SHOWERS AND ISOLATED TSTMS ARE NOTED ACROSS THE YUCATAN CHANNEL UNDER A SE LOW LEVEL WIND FLOW. SOME SHOWERS ARE NEAR THE WINDWARD ISLAND IN ASSOCIATION WITH A SURFACE TROUGH THAT HAS MOVED LITTLE SINCE YESTERDAY. THIS TROUGH EXTENDS ACROSS THE TROPICAL N ATLC FROM 18N57W TO 10N62W. AN EARLIER ASCAT PASS REVELED THE WIND SHIFT RELATED TO THIS FEATURE. SOME SHOWER ACTIVITY IS ALSO NOTED OVER THE SW CARIBBEAN IN THE VICINITY OF SAN ANDRES. WINDS ARE FORECAST TO INCREASE ACROSS THE NW CARIBBEAN ON SAT AHEAD OF THE COLD FRONT FORECAST TO MOVE ACROSS THE GULF OF MEXICO THIS WEEKEND. THE SOUTHERN PORTION OF THE COLD FRONT WILL MOVE ACROSS THE YUCATAN CHANNEL SAT EVENING REACHING FROM CENTRAL CUBA TO NEAR CABO GRACIAS A DIOS NICARAGUA LATE SUN. FRESH W TO NW WINDS ARE EXPECTED BEHIND THE FRONT. ALOFT...NEAR ZONAL WESTERLY FLOW DOMINATES THE CARIBBEAN SEA. ATLANTIC OCEAN... A SHORTWAVE ALONG THE COAST OF SE U.S. SUPPORTS A WEAK TROUGH EXTENDING FROM 31N79W TO THE COAST OF FLORIDA NEAR MELBOURNE. SCATTERED SHOWERS AND TSTMS ARE AHEAD OF THE TROUGH AXIS JUST N OF THE NW BAHAMAS. THE REMAINDER OF THE WESTERN ATLC IS UNDER THE INFLUENCE OF A WEAK RIDGE ANCHORED ON A 1018 MB HIGH LOCATED NEAR BERMUDA. THIS SYSTEM IS MAINTAINING MOSTLY FAIR WEATHER CONDITIONS AND LIGHT WINDS ACROSS THE REGION BETWEEN 55W AND THE BAHAMAS. SW AND W OF THIS RIDGE...SE TO S WINDS OF 10 TO 15 KT ARE BLOWING. THESE WINDS WILL FURTHER INCREASE TO 25 TO 30 KT LATE SAT AHEAD OF THE DEVELOPING LOW PRES AND STRONG COLD FRONT FORECAST TO MOVE ACROSS THE GULF OF MEXICO. THE COLD FRONT IS EXPECTED TO MOVE OFF THE SE U.S. COAST BY SUN. A WEAK LOW PRES REMAINS OVER THE FORECAST REGION NEAR 30N49W. THIS LOW IS FORECAST TO DISSIPATE IN ABOUT 24 HOURS. THE ATTENDANT WEAKENING COLD FRONT IS WELL DISPLACED TO THE EAST AND ENTERS THE AREA NEAR 31N43W THEN CONTINUES SW TO 26N45W. WHERE IT BEGINS TO DISSIPATE. FRESH TO STRONG SLY WINDS ARE SEEN AHEAD OF THE FRONT PER THE MOST RECENT ASCAT PASS DUE TO THE PRES GRADIENT BETWEEN THE LOW PRES AND A HIGH CENTERED NEAR THE AZORES. THIS HIGH EXTENDS A RIDGE OVER THE EASTERN ATLC. AS PREVIOUSLY MENTIONED...A SURFACE TROUGH IS OVER THE TROPICAL N ATLC WATERS JUST E OF THE LESSER ANTILLES AND IS GENERATING SOME SHOWER ACTIVITY. ACCORDING TO THE COMPUTER MODEL...MOISTURE ASSOCIATED WITH THIS TROUGH WILL REMAIN NEAR THE LESSER ANTILLES THIS UPCOMING WEEKEND. A BAND OF TRANSVERSE HIGH CLOUDS ASSOCIATED WITH STRONG UPPER-LEVEL WINDS EXTENDS FROM NORTHERN SOUTH AMERICA ACROSS THE WINDWARD ISLANDS INTO THE ATLC AROUND THE BASE OF AN UPPER LEVEL TROUGH EXTENDING BETWEEN 40W AND 50W...THEN UP ACROSS THE N PORTION OF A RIDGE ANCHORED ON A HIGH NEAR 6N37W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GR