000 AXNT20 KNHC 181743 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON MAY 18 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 1715 UTC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 44W/45W S OF 12N TO 3N MOVING W NEAR 10 KT. THIS WAVE IS EMBEDDED WITHIN BROAD SURFACE CYCLONIC FLOW WITH VISIBLE IMAGERY SHOWING AN INVERTED-V CLOUD PRESENTATION IN THE LOW-LEVEL CLOUD FIELD S OF 6N BETWEEN 42W-47W. AN EARLIER ASCAT PASS AROUND 1200 UTC SHOWED 15-20 KT WINDS IN THE VICINITY OF THE WAVE AXIS WITH ISOLATED MODERATE CONVECTION FROM 1N-5N BETWEEN 43W-47W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 5N10W 1N20W CROSSING THE EQUATOR NEAR 24W EXTENDING TO 2S38W AND INTO NE BRAZIL NEAR 1S46W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 2N-6N BETWEEN 10W-17W. SIMILAR CONVECTION IS S OF 5N BETWEEN 19W-26W. ...DISCUSSION... GULF OF MEXICO... A DEEP LAYER TROUGH OVER THE ERN CONUS IS ASSOCIATED WITH A SURFACE STATIONARY FRONT OVER THE FLORIDA PENINSULA AND E GULF THAT AT 1500 UTC EXTENDS FROM TITUSVILLE FLORIDA TO TAMPA BAY AND ALONG 27N86W 24N89W CLIPPING THE NW YUCATAN PENINSULA AND ALONG THE COAST TO 19N92W. ALSO...A SURFACE TROUGH IS LOCATED TO THE E OF THE FRONT AND EXTENDS FROM NEAR 28N84W TO 22N85W. LOW LEVEL CONVERGENCE NEAR THE STATIONARY FRONT AND SURFACE TROUGH IS SUPPORTING NUMEROUS SHOWERS AND SCATTERED TSTMS OVER THE GULF N OF 24N E OF 88W TO OVER THE FLORIDA PENINSULA AND INTO THE W ATLC. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THE AFOREMENTIONED DEEP TROUGH AND AN UPPER LEVEL RIDGE OVER THE SW GULF. THE FRONT IS EXPECTED TO GRADUALLY WEAKEN ACROSS THE GULF DURING THE NEXT DAY...AS MANY OF THE GLOBAL MODELS ARE SHOWING LOW PRESSURE DEVELOPING OVER THE SW NORTH ATLC AND SE GULF...EITHER EXTRATROPICAL OR SUBTROPICAL...AND MOVE GENERALLY N. THE DEVELOPMENT AND TRACK OF THE LOW REMAINS UNCERTAIN...THOUGH COMPUTER MODELS SUGGEST THAT WINDS WILL INCREASE AROUND THE LOW. CARIBBEAN SEA... SCATTERED SHOWERS AND TSTMS ARE AFFECTING PORTIONS OF THE NORTH CENTRAL CARIBBEAN N OF 15N BETWEEN 68W-77W...INCLUDING E CUBA... HISPANIOLA AND THE WINDWARD PASSAGE. THIS ACTIVITY IS BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH THAT EXTENDS FROM EXUMA SOUND IN THE BAHAMAS ACROSS ERN CUBA TO 16N76W. THE ACTIVITY IS ALSO BEING SUPPORTED BY MIDDLE TO UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER RIDGE OVER THE SW NORTH ATLC AND AN UPPER TROUGH OVER THE CENTRAL CARIBBEAN. DURING THE NEXT DAY...A SURFACE LOW IS FORECAST TO DEVELOP ALONG THE SURFACE TROUGH AND MOVE N OF THE CARIBBEAN BY TUESDAY. UPPER LEVEL DIVERGENCE AND ATMOSPHERIC INSTABILITY ASSOCIATED WITH THE UPPER TROUGH OVER THE CENTRAL CARIBBEAN IS ALSO SUPPORTING SCATTERED SHOWERS OVER THE NE CARIBBEAN N OF 16N...IMPACTING PUERTO RICO...THE VIRGIN AND LEEWARD ISLANDS. ATLANTIC OCEAN... AN OCCLUDED 1009 MB SURFACE LOW IS QUASI-STATIONARY NEAR 32N52W. AN ASSOCIATED SURFACE STATIONARY FRONT EXTENDS FROM 30N45W TO 25N46W TO 22N50W W-SW TO NEAR BARBUDA. LOW-LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS ALONG AND WITHIN 250 NM E OF THE SURFACE FRONT N OF 22N. S OF 22N...SCATTERED SHOWERS ARE WITHIN 60 NM EITHER SIDE OF THE FRONT. A SURFACE TROUGH IS ALSO ANALYZED TO THE W OF THE STATIONARY FRONT AND EXTENDS FROM 31N49W TO 28N49W TO 24N57W. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 30 NM EITHER SIDE OF THIS SURFACE TROUGH. ALL OF THIS SHOWER AND THUNDERSTORM ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE IN THE ERN SEMICIRCLE OF AN UPPER LOW NEAR 32N52W. FARTHER TO THE W...A SURFACE RIDGE EXTENDS SW FROM A SURFACE HIGH PRESSURE CENTERED NW OF BERMUDA. SUBSIDENCE AND ATMOSPHERIC STABILITY ASSOCIATED WITH AN UPPER RIDGE OVER THE SW NORTH ATLC...IS SUPPORTING GENERALLY FAIR WEATHER CONDITIONS BETWEEN 57W-73W. HOWEVER...MOIST SELY LOW LEVEL FLOW OVER PORTIONS OF THE SW NORTH ATLC IS SUPPORTING SCATTERED SHOWERS AND TSTMS W OF 72W ALL FOCUSED ON A STATIONARY FRONT THAT ENTERS THE REGION NEAR 32N77W EXTENDING SW TO NEAR TITUSVILLE FLORIDA. ADDITIONALLY...SCATTERED SHOWERS AND TSTMS ASSOCIATED WITH THE SURFACE TROUGH OVER THE CENTRAL CARIBBEAN ACROSS ERN CUBA TO 23N76W ARE MOVING NWD INTO THE W ATLC IMPACTING THE WINDWARD PASSAGE...TURKS AND CAICOS ISLANDS AS WELL AS THE BAHAMAS. DURING THE NEXT DAY...MANY OF THE GLOBAL MODELS ARE SHOWING LOW PRESSURE DEVELOPING OVER THE SW NORTH ATLC AND SE GULF OF MEXICO...EITHER EXTRATROPICAL OR SUBTROPICAL...AND MOVING GENERALLY NWD. THE PRESSURE GRADIENT AROUND THE LOW IS FORECAST TO RESULT IN GALE CONDITIONS N OF 29N W OF 76W EARLY TUESDAY THROUGH WEDNESDAY. ACROSS THE E ATLC...A SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW ALOFT IS OBSERVED AND FAIR WEATHER CONDITIONS PERSIST. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS PRESENT S OF 12N E OF 58W WITH UPPER LEVEL HIGHS CENTERED NEAR 6N26W AND 5N48W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL HIGHS AND RIDGE IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ. $$ HUFFMAN