000 AXNT20 KNHC 120002 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SAT MAY 11 2013 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. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM NEAR THE SENEGAL/GUINEA BISSAU BORDER TO 7N24W. THE INTERTROPICAL CONVERGENCE ZONE AXIS CONTINUES FROM 7N24W TO 3N35W TO THE COAST OF BRAZIL AT 1N50W. NO SIGNIFICANT CONVECTION ALONG THE ITCZ/MONSOON TROUGH AXES. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS LOCATED N OF 3N TO THE COAST OF AFRICA BETWEEN THE PRIME MERIDIAN AND 7W. ...DISCUSSION... GULF OF MEXICO... A WEAK COLD FRONT MOVED EASTWARD IN THE NW GULF THIS AFTERNOON. AS OF 1800 UTC...IT EXTENDS FROM CENTRAL LOUISIANA TO NE MEXICO. SOME HEAVY SHOWERS AND THUNDERSTORMS ARE NOTED AHEAD OF THE FRONT IMPACTING THE NORTHEASTERN GULF WATERS. A DIFFLUENT PATTERN ALOFT IS HELPING TO ENHANCE THIS CONVECTIVE ACTIVITY. THE FRONT WILL EXTEND FROM THE FLORIDA BIG BEND TO THE CENTRAL BAY OF CAMPECHE TOMORROW MORNING. THE NORTHERN SEGMENT OF THE FRONT TO THE N OF 26N WILL MOVE E OF THE AREA SUN NIGHT WHILE THE SOUTHERN PORTION WILL GRADUALLY DISSIPATE FROM S FLORIDA TO THE CENTRAL BAY OF CAMPECHE SUN THROUGH MON. CURRENTLY...A TROUGH EXISTS IN THE BAY OF CAMPECHE NORTHEASTWARD TO THE CENTRAL GULF AHEAD OF THE FRONT...THOUGH NOT SIGNIFICANT WEATHER IS ASSOCIATED WITH THIS FEATURE. GENTLE TO MODERATE SOUTHEASTERLY WIND FLOW IS OBSERVED IN MOST OF THE GULF...WITH MODERATE TO FRESH NORTHEASTERLY WINDS ON THE WEST SIDE OF THE TROUGH AND FRONT. ALOFT...AN UPPER LEVEL RIDGE CENTERED OVER NORTHERN CENTRAL AMERICA COVERS THE MAJORITY OF THE GULF AND SE MEXICO...INCLUDING THE YUCATAN PENINSULA. CARIBBEAN SEA... TRADE WIND FLOW OF 10-15 KT DOMINATES THE MAJORITY OF THE EASTERN AND CENTRAL CARIBBEAN WITH WINDS OF 20 TO 25 KT NEAR THE COAST OF COLOMBIA. NO SIGNIFICANT DEEP CONVECTION IS OCCURRING OVER THE CARIBBEAN THIS AFTERNOON...THOUGH DIURNALLY-AIDED THUNDERSTORM ACTIVITY IS PRESENT OVER PORTIONS OF CENTRAL AMERICA FROM BELIZE TO COSTA RICA. THIS CONVECTION MAY BE CONTRIBUTED TO BY A WEAK LOW NEAR 10N85W OVER NW COSTA RICA WITH TROUGHING EXTENDING NORTH-SOUTH. ALOFT...THE UPPER ANTICYCLONE CENTERED OVER NORTHERN CENTRAL AMERICA ALSO EXTENDS A RIDGE ACROSS THE WESTERN CARIBBEAN PROVIDING MOSTLY FAIR CONDITIONS THERE. AN UPPER LEVEL TROUGH PERSISTS ACROSS THE EASTERN CARIBBEAN EXTENDING FROM THE MONA PASSAGE TO NORTHERN COLOMBIA. STRONG UPPER LEVEL SUBSIDENCE AND DRY AIR MASS HAS INVADED HISPANIOLA LIMITING THE DEVELOPMENT OF SHOWER AND TSTM ACTIVITY. PUERTO RICO AND THE VIRGIN ISLANDS ARE ON THE EAST SIDE OF THE UPPER TROUGH. THIS TROUGH WILL COMBINE WITH LOCAL EFFECTS AND DIURNAL HEATING TO PRODUCE SOME SHOWERS AND TSTMS OVER THOSE ISLANDS MAINLY DURING THE AFTERNOONS OF THE NEXT COUPLE OF DAYS. ATLANTIC OCEAN... A RIDGE/TROUGH/RIDGE/TROUGH PATTERN DOMINATES THE DISCUSSION AREA. AN UPPER LOW IS LOCATED NEAR 24N65W SUPPORTS A 1012 MB SURFACE LOW PRES CENTERED NEAR 23N66W. SCATTEROMETER AND BUOY 41043 INDICATE THE PRESENCE OF A CLOSED LOW WITH A TROUGH EXTENDING TO ITS SOUTHWEST. DEEP CONVECTION HAS PERSISTED IN ASSOCIATION WITH THE LOW TODAY. SHOWERS AND TSTMS ARE E OF THE LOW CENTER...COVERING THE AREA FROM 21N TO 26N BETWEEN 62W AND 65W. ENVIRONMENTAL CONDITIONS...ESPECIALLY THE VERTICAL SHEAR...DO NOT APPEAR TO BE CONDUCIVE FOR TROPICAL DEVELOPMENT. THE SURFACE LOW IS FORECAST TO DRIFT TOWARD HISPANIOLA WHILE WEAKENING TO A TROUGH BY LATE SUN. THIS TROUGH WILL MOVE WESTWARD BEFORE DISSIPATING BY LATE MON. CURRENTLY...PRESSURE GRADIENT BETWEEN THE SURFACE LOW AND A RIDGE EXTENDING FROM BERMUDA TO SOUTH FLORIDA IS PRODUCING A LARGE AREA OF FRESH TO STRONG WINDS TO N...NE AND SE QUADRANTS OF THE LOW... PARTICULARLY S OF 27N BETWEEN 58W AND 68W. THE CENTRAL ATLC IS DOMINATED BY BROAD SURFACE RIDGING SUPPORTED BY AN UPPER LEVEL RIDGE ALONG 52W. AN UPPER LEVEL TROUGH COVERS THE EASTERN ATLANTIC CENTERED AROUND AN UPPER LOW NEAR 31N32W. THE UPPER LOW SUPPORTS A WEAK 1020 MB SURFACE LOW NEAR 30N32W. A SURFACE TROUGH EXTENDS FROM THE LOW CENTER TO NEAR 24N35W. SCATTERED SHOWERS AND TSTMS ARE NOTED MAINLY ON THE NORTH SIDE OF THE LOW CENTER AND AHEAD OF THE TROUGH AXIS. THIS SURFACE LOW IS EXPECTED TO DISSIPATE ON SUN. AN AREA OF SAHARAN DUST IS OBSERVED ON VIS AND SAHARAN AIR LAYER SATELLITE IMAGERY REACHING 47W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE AT THE REQUEST OF METEO-FRANCE AND THE METEOROLOGICAL SERVICES OF HAITI AND THE DOMINICAN REPUBLIC...THE TROPICAL ANALYSIS AND FORECAST BRANCH (TAFB) WILL BEGIN PROVIDING...ON A TEMPORARY BASIS...A SEPARATE DETAILED SECTION WITHIN THE ATLANTIC TROPICAL WEATHER DISCUSSION (TWDAT). IT WILL COVER BOTH HAITI AND THE DOMINICAN REPUBLIC DUE TO THE SHARED GEOGRAPHY OF BOTH COUNTRIES ON THE ISLAND OF HISPANIOLA. THE SECTION BEGINS ON MAY 15 2013 AT 1800 UTC...2 PM EDT. IT WILL PROVIDE GUIDANCE FOR SIGNIFICANT WEATHER EVENTS THAT ARE EXPECTED TO IMPACT THE REGION THROUGH 48 HOURS...WITH THE FOCUS ON ASSESSING THE POTENTIAL FOR HEAVY RAINFALL. $$ GR/CWL