000 AXNT20 KNHC 222353 AAA TWDAT TROPICAL WEATHER DISCUSSION...UPDATED NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT FRI MAY 22 2009 ...UPDATED INFORMATION REGARDING SURFACE LOW IN THE GULF OF MEXICO... 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 2245 UTC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 37W/38W SOUTH OF 7N MOVING WEST NEAR 15 KT. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SATELLITE IMAGERY INDICATES CYCLONIC CIRCULATION IN THE MOTION OF LOW LEVEL CLOUDS IN THE VICINITY OF THE WAVE. SUBSIDENCE IN THE VICINITY OF A SURFACE RIDGE OVER THE E ATLC IS PREVENTING THE DEVELOPMENT OF DEEP CONVECTION NEAR THIS WAVE...HOWEVER SCATTERED SHOWERS ARE WITHIN 90 NM EITHER SIDE OF THE WAVE AXIS FROM 1N-6N. A TROPICAL WAVE IS ALONG 82W SOUTH OF 12N MOVING WEST NEAR 15 KT. THIS WAVE IS ALSO ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. LOW LEVEL CYCLONIC TURNING IS NOTED OVER THE SW CARIBBEAN DUE TO THE COMBINATION OF THE WAVE AND A 1006 MB LOW E OF THE WAVE AXIS OVER N COLOMBIA NEAR 8N74W. SCATTERED MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF THE WAVE AXIS S OF 11N...INCLUDING THE COASTS OF COSTA RICA AND PANAMA. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 6N10W 4N19W 1N28W CROSSING THE EQUATOR NEAR 40W EXTENDING TO NE BRAZIL NEAR 1S46W. SCATTERED MODERATE CONVECTION IS S OF 3N BETWEEN 6W-9W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS S OF 5N BETWEEN 14W-27W. SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 41W-46W. ...DISCUSSION... GULF OF MEXICO... A DEEP LAYER TROUGH IS PRESENT ACROSS THE GULF WITH AN UPPER LEVEL LOW NEAR 28N88W AND AN ASSOCIATED 1007 MB SURFACE LOW NEAR 27N87W. A SURFACE TROUGH EXTENDS FROM THE SURFACE LOW TO THE N YUCATAN PENINSULA NEAR 21N87W. LOW LEVEL CONVERGENCE NEAR THE SURFACE LOW AND SURFACE TROUGH...AS WELL AS UPPER LEVEL DIFFLUENCE E OF THE UPPER LOW...ARE SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE GULF N OF 23N E OF 89W....INCLUDING COASTAL WATERS OF FLORIDA. THE TIGHT SURFACE PRESSURE GRADIENT BETWEEN THE SURFACE LOW AND A SURFACE RIDGE OVER THE SE CONUS IS SUPPORTING WIND SPEEDS OF 20 TO 25 KT AROUND THE LOW ACROSS N PORTIONS OF THE MIDDLE GULF. THE SURFACE LOW IS FORECAST TO MOVE NORTHWARD DURING THE NEXT DAY AND BE LOCATED NEAR 30N89W AS A 1008 MB SURFACE LOW AT 23/1800 UTC. ADDITIONAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE...AND A TROPICAL DEPRESSION COULD FORM BEFORE THE LOW MOVES INLAND OVER THE NORTHERN GULF COAST ON SATURDAY. IF NECESSARY...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL INVESTIGATE THE LOW TOMORROW. THERE IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. REGARDLESS OF DEVELOPMENT... HEAVY RAINS AND OCCASIONALLY GUSTY WINDS ARE EXPECTED ALONG PORTIONS OF THE NORTHERN GULF COAST TONIGHT AND SATURDAY. THE WINDS AROUND THE LOW ARE FORECAST TO BECOME LIGHTER LATE THIS WEEKEND AS THE PRESSURE GRADIENT AROUND THE LOW RELAXES. ACROSS THE W GULF...SUBSIDENCE ASSOCIATED WITH NORTHWESTERLY FLOW ALOFT IS SUPPORTING GENERALLY FAIR WEATHER CONDITIONS...WITH UPPER LEVEL MOISTURE AND HIGH LEVEL CLOUDS STREAMING SOUTHEASTWARD. NW TO N WINDS UP TO 20 KT ARE OCCURRING ACROSS PORTIONS OF THE NW GULF. ADDITIONALLY...RECENT VISIBLE SATELLITE IMAGERY INDICATES THAT AN AREA OF SMOKE ENTRAINED WITHIN THE LOW LEVEL SOUTHWESTERLY FLOW AROUND THE AFOREMENTIONED LOW IS DRIFTING NORTHEASTWARD FROM THE N YUCATAN PENINSULA ACROSS THE SE GULF...POTENTIALLY REDUCING VISIBILITIES. CARIBBEAN SEA... SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS PERSIST ACROSS THE E CARIBBEAN FROM 14N-18N BETWEEN 64W-71W. THIS ACTIVITY IS BEING SUPPORTED BY UPPER LEVEL DIVERGENCE IN MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE W CARIBBEAN AND GULF OF MEXICO...AND AN UPPER LEVEL RIDGE ACROSS THE E CARIBBEAN AND SW NORTH ATLC. THE UPPER LEVEL DIVERGENCE AND ASSOCIATED SHOWER AND THUNDERSTORM ACTIVITY ARE CURRENTLY WEAKENING. HOWEVER...ADDITIONAL SHOWERS AND THUNDERSTORMS COULD AFFECT NORTHERN PORTIONS OF THE CARIBBEAN DURING THE NEXT COUPLE OF DAYS WITH THE UPPER TROUGH AND ASSOCIATED ATMOSPHERIC INSTABILITY PERSISTING OVER THE CARIBBEAN. ADDITIONALLY...ATMOSPHERIC INSTABILITY NEAR THE UPPER TROUGH IS RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS OVER CUBA...HISPANIOLA...PUERTO RICO...AND NEARBY COASTAL WATERS...AS WELL AS OVER THE W CARIBBEAN FROM 14N-19N BETWEEN 77W-86W. UPPER LEVEL MOISTURE AND HIGH LEVEL CLOUDS ARE STREAMING GENERALLY EASTWARD ACROSS THE CARIBBEAN. MEANWHILE...THE SURFACE PRESSURE GRADIENT S OF A SURFACE RIDGE OVER THE CENTRAL ATLC IS MAINTAINING E TO SE WINDS UP TO 20 KT ACROSS PORTIONS OF THE E CARIBBEAN. ADDITIONALLY...A TROPICAL WAVE IS OVER THE SW CARIBBEAN WITH SCATTERED MODERATE CONVECTION AFFECTING THE COASTS OF COSTA RICA AND PANAMA. PLEASE SEE ABOVE FOR FURTHER INFORMATION ON THIS TROPICAL WAVE. ATLANTIC OCEAN... SCATTERED SHOWERS AND THUNDERSTORMS ARE OCCURRING S OF 30N W OF 74W INCLUDING THE NW BAHAMAS AND THE COAST OF FLORIDA...AS WELL AS S OF 24N BETWEEN 64W-74W INCLUDING CUBA...HISPANIOLA...PUERTO RICO...AND THE SE BAHAMAS. THIS ACTIVITY IS BEING SUPPORTED BY UPPER LEVEL DIFFLUENCE IN MOIST SOUTHWESTERLY FLOW ALOFT BETWEEN AN UPPER LEVEL TROUGH OVER THE GULF OF MEXICO AND W CARIBBEAN... AND AN UPPER LEVEL RIDGE ACROSS THE SW NORTH ATLC AND E CARIBBEAN. ATMOSPHERIC INSTABILITY NEAR THE UPPER LEVEL TROUGH IS ALSO SUPPORTING THE SHOWER AND THUNDERSTORM ACTIVITY. FARTHER TO THE E...AN UPPER LEVEL TROUGH IS PRESENT WITH AN AXIS EXTENDING FROM AN UPPER LEVEL LOW NEAR 31N55W TO 27N52W TO 25N50W. 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 THUNDERSTORMS N OF 24N BETWEEN 43W-55W. THIS ACTIVITY IS ALSO BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH EXTENDING FROM 31N51W TO A 1016 MB SURFACE LOW NEAR 27N57W CONTINUING TO 22N62W TO 21N68W. THIS LOW LEVEL CONVERGENCE IS ALSO SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FROM 17N-22N BETWEEN 57W-65W. DURING THE NEXT DAY...THE 1016 MB SURFACE LOW IS FORECAST TO DISSIPATE. 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 PRESENT N OF 27N E OF 18W WITH AN ASSOCIATED SURFACE TROUGH EXTENDING FROM 27N17W TO THE CANARY ISLANDS NEAR 29N14W TO 32N10W TO N OF THE DISCUSSION AREA. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS WITHIN 60 NM EITHER SIDE OF THIS SURFACE TROUGH. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS S OF 11N E OF 41W WITH AN UPPER LEVEL HIGH NEAR 7N28W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL HIGH AND UPPER LEVEL RIDGE IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ. $$ COHEN