000 AXNT20 KNHC 230559 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 AM EDT SAT MAY 23 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...SPECIAL FEATURE... A 1006 MB SURFACE LOW IS LOCATED NEAR 28N87W...OR ABOUT 150 NM SOUTH OF MOBILE ALABAMA. A SURFACE TROUGH EXTENDS FROM THE SURFACE LOW TO THE NRN YUCATAN PENINSULA NEAR 22N89W. LOW LEVEL CONVERGENCE NEAR THE SURFACE LOW...ALONG WITH DIFFLUENCE ASSOCIATED WITH A MIDDLE TO UPPER LEVEL TROUGH AXIS ACROSS THE CENTRAL GULF ARE SUPPORTING NUMEROUS SHOWERS AND SCATTERED TSTMS ACROSS THE GULF N OF 27N E OF 90W....INCLUDING THE NE GULF COAST. THE SURFACE LOW IS FORECAST TO MOVE N-NW DURING THE NEXT 24 HOURS AND LOCATE INLAND OVER SRN MISSISSIPPI. HOWEVER... ADDITIONAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE...AND A TROPICAL DEPRESSION COULD FORM BEFORE THE LOW MOVES INLAND OVER THE NRN GULF COAST ON SATURDAY. REGARDLESS OF DEVELOPMENT... HEAVY RAINS AND OCCASIONALLY GUSTY WINDS ARE EXPECTED ALONG PORTIONS OF THE NRN GULF COAST TONIGHT AND SATURDAY. INTERESTS IN THIS AREA SHOULD MONITOR THE PROGRESS OF THE SYSTEM. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 39W/40W S OF 7N MOVING W NEAR 15 KT. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS WITH SATELLITE IMAGERY INDICATING INVERTED-V SIGNATURE AND WEAK CYCLONIC CURVATURE NEAR THE WAVE AXIS IN THE LOW LEVEL CLOUDS. SUBSIDENCE IN THE VICINITY OF A SURFACE RIDGE OVER THE ERN ATLC IS PREVENTING THE DEVELOPMENT OF DEEP CONVECTION NEAR THE NRN EXTENT OF THE WAVE...HOWEVER SCATTERED SHOWERS ARE WITHIN 300 NM EITHER SIDE OF THE WAVE AXIS S OF 4N. A TROPICAL WAVE IS ALONG 83W S OF 12N MOVING W NEAR 15 KT. THIS WAVE EXTENDS INTO THE E PACIFIC REGION AND IS ALSO ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. LOW LEVEL CYCLONIC TURNING IS NOTED OVER WRN PANAMA DUE TO THE COMBINATION OF THE WAVE AND A 1006 MB LOW E OF THE WAVE AXIS OVER NRN COLOMBIA NEAR 7N74W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM EITHER SIDE OF THE WAVE AXIS S OF 10N...INCLUDING INLAND COSTA RICA AND PANAMA. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 7N12W 3N26W 1N37W CROSSING THE EQUATOR NEAR 40W EXTENDING TO NE BRAZIL NEAR 2S45W. SCATTERED MODERATE CONVECTION IS S OF 3N BETWEEN 40W-49W. ...DISCUSSION... GULF OF MEXICO... A DEEP LAYER TROUGH IS PRESENT ACROSS THE GULF WITH THE UPPER LEVEL TROUGH AXIS EXTENDING FROM TEXAS TO THE FLORIDA KEYS. THE ASSOCIATED SURFACE FEATURE...A 1006 MB LOW NEAR 28N87W IS GENERATING NUMEROUS SHOWERS AND TSTMS...AS WELL AS STRONGER WINDS...AS THIS LOW PRESSURE AREA PUSHES UP AGAINST A HIGH PRESSURE RIDGE ACROSS THE SE CONUS. FOR MORE DETAILS ON THIS SYSTEM SEE SPECIAL FEATURE SECTION ABOVE. ACROSS THE W GULF... SUBSIDENCE ASSOCIATED WITH W-NW FLOW ALOFT IS SUPPORTING GENERALLY FAIR WEATHER CONDITIONS...WITH UPPER LEVEL MOISTURE AND HIGH LEVEL DEBRIS CLOUDS FROM SCATTERED SHOWERS/ISOLATED TSTMS ACROSS CENTRAL MEXICO STREAMING EWD. GENERALLY LIGHT NLY WINDS ARE OBSERVED ACROSS PORTIONS OF THE WRN GULF W OF 90W. CARIBBEAN SEA... SCATTERED SHOWERS AND ISOLATED TSTMS PERSIST ACROSS THE ERN CARIBBEAN N OF 14N BETWEEN 63W-71W. THIS ACTIVITY IS BEING DRIVEN BY UPPER LEVEL DIVERGENCE IN MOIST SWLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE WRN CARIBBEAN AND GULF OF MEXICO...AND AN UPPER LEVEL RIDGE ACROSS THE SE CARIBBEAN. THIS ACTIVITY IS EXPECTED TO CONTINUE OVER THE NEXT COUPLE OF DAYS ACROSS THE NRN CARIBBEAN AS THE UPPER SHORTWAVE TROUGH SHIFTS EWD ACROSS THE GREATER ANTILLES BRINGING INCREASED CHANCES FOR SCATTERED SHOWERS. CLOSER TO THE UPPER LEVEL TROUGH AXIS ACROSS THE WRN CARIBBEAN...ISOLATED SHOWERS ARE OBSERVED OVER CUBA... JAMAICA...HISPANIOLA AND NEARBY WRN CARIBBEAN WATERS FROM 14N-20N BETWEEN 75W-82W. MEANWHILE...THE SURFACE PRESSURE GRADIENT SW OF A SURFACE RIDGE OVER THE CENTRAL ATLC IS MAINTAINING ELY WINDS UP TO 20 KT ACROSS PORTIONS OF THE ERN CARIBBEAN. ADDITIONALLY...THE NRN EXTENT OF A TROPICAL WAVE IS OVER THE SW CARIBBEAN WITH SCATTERED MODERATE CONVECTION S OF 10N INLAND OVER COSTA RICA AND PANAMA. ATLANTIC OCEAN... SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING S OF 32N W OF 75W INCLUDING THE BAHAMAS AND THE COAST OF FLORIDA. THIS ACTIVITY IS BEING SUPPORTED BY UPPER LEVEL DIFFLUENCE IN MOIST SWLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE GULF OF MEXICO AND WRN CARIBBEAN...AND AN UPPER LEVEL RIDGE ACROSS THE SW NORTH ATLC. FARTHER TO THE E...AN UPPER LEVEL TROUGH IS PRESENT WITH AN AXIS EXTENDING FROM AN UPPER LEVEL LOW NEAR 30N53W TO 27N60W TO 27N68W. ATMOSPHERIC INSTABILITY NEAR THE UPPER LEVEL LOW AND TROUGH...AS WELL AS UPPER LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT...ARE SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS WITHIN 200 NM EITHER SIDE OF A LINE FROM 32N44W 24N50W 22N63W SWD TO OVER THE NE CARIBBEAN SEA. THIS ACTIVITY IS ALSO BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH EXTENDING FROM 30N52W TO A 1017 MB SURFACE LOW NEAR 27N58W CONTINUING TO 19N64W. ACROSS THE E ATLC...A SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW ALOFT IS OCCURRING AND FAIR WEATHER CONDITIONS PERSIST. HOWEVER...AN UPPER LEVEL TROUGH IS OBSERVED N OF 26N E OF 18W WITH AN ASSOCIATED SURFACE TROUGH EXTENDING FROM 31N10W TO E OF THE CANARY ISLANDS NEAR 27N14W. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS S OF 15N E OF 40W WITH AN UPPER LEVEL HIGH NEAR 7N29W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL HIGH AND UPPER LEVEL RIDGE IS ENHANCING THE SHOWER ACTIVITY ASSOCIATED WITH THE ITCZ. $$ HUFFMAN