000 AXNT20 KNHC 182325 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2245 UTC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 45W/46W S OF 12N TO 2N MOVING W NEAR 10 KT. THIS WAVE IS EMBEDDED WITHIN A BROAD INVERTED-V STRUCTURE IN THE LOW-LEVEL CLOUD COVERAGE...AND IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SCATTERED MODERATE CONVECTION IS OCCURRING WITHIN 90 NM EITHER SIDE OF THE WAVE S OF 6N. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 5N9W 2N18W CROSSING THE EQUATOR NEAR 28W EXTENDING TO 2S36W AND INTO NE BRAZIL NEAR 3S45W. SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 1W-3W. SCATTERED MODERATE CONVECTION IS ALSO S OF 2N BETWEEN 7W-9W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS S OF 6N BETWEEN 15W-21W. SCATTERED MODERATE CONVECTION IS S OF 2N BETWEEN 26W-29W. ...DISCUSSION... GULF OF MEXICO... A DEEP LAYER TROUGH OVER THE E CONUS AND E GULF IS ASSOCIATED WITH A SURFACE COLD OVER THE E GULF THAT EXTENDS FROM THE SOUTH FLORIDA PENINSULA NEAR 26N82W TO 26N83W. FARTHER TO THE SW...A NEWLY-DEVELOPED 1010 MB SURFACE LOW IS LOCATED NEAR 25N85W... WITH A SURFACE TROUGH EXTENDING FROM 26N84W TO THE SURFACE LOW TO 22N85W. THIS SURFACE LOW IS LOCATED BENEATH THE SOUTHWESTERN PORTION OF THE DEEP LAYER TROUGH THAT EXTENDS INTO THE E GULF. LOW LEVEL CONVERGENCE NEAR THE LOW...TROUGH...AND COLD FRONT IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER THE GULF FROM 23N-29N E OF 87W...INCLUDING THE CENTRAL AND SOUTH FLORIDA PENINSULA...THE STRAITS OF FLORIDA...THE FLORIDA KEYS...AND W CUBA. THIS SHOWER AND THUNDERSTORM ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THE AFOREMENTIONED DEEP TROUGH AND AN UPPER LEVEL RIDGE OVER THE SW NORTH ATLC. DURING THE NEXT DAY...THE SURFACE LOW IS FORECAST TO MOVE EASTWARD AND BE LOCATED OVER THE FLORIDA KEYS NEAR 25N81W AS A 1009 MB SURFACE LOW AT 19/1800 UTC. HOWEVER...THE FUTURE DEVELOPMENT AND TRACK OF THE LOW REMAIN UNCERTAIN...THOUGH COMPUTER MODEL GUIDANCE SUGGESTS THAT WINDS WILL INCREASE AROUND THE LOW...WHICH WILL AFFECT PORTIONS OF THE GULF OF MEXICO. ACROSS THE WEST GULF... DEEP LAYER DRY AIR...AS WELL AS SUBSIDENCE WITH CONFLUENT UPPER LEVEL NORTHWESTERLY FLOW...ARE RESULTING IN GENERALLY FAIR WEATHER CONDITIONS. ALSO...N TO NE SURFACE WINDS ARE OCCURRING ACROSS THE W GULF...WITH WIND SPEEDS UP TO 25 KT ACROSS PORTIONS OF THE NW GULF. CARIBBEAN SEA... SCATTERED SHOWERS AND THUNDERSTORMS ARE AFFECTING PORTIONS OF THE N CARIBBEAN N OF 17N BETWEEN 67W-78W...INCLUDING JAMAICA... HISPANIOLA...AND E CUBA. THIS ACTIVITY IS BEING SUPPORTED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER LEVEL TROUGH OVER THE CARIBBEAN WITH AN AXIS EXTENDING FROM 18N72W TO 13N73W TO 11N74W. ADDITIONALLY...ATMOSPHERIC INSTABILITY IS RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS OVER HONDURAS...W CUBA AND E PORTIONS OF THE YUCATAN PENINSULA...IMPACTING THE ADJACENT COASTAL WATERS...WITH SCATTERED SHOWERS AND THUNDERSTORMS ALSO OVER PANAMA AND COSTA RICA. UPPER LEVEL MOISTURE AND HIGH LEVEL CLOUDS ARE STREAMING SOUTHEASTWARD ACROSS THE W CARIBBEAN AND NORTHEASTWARD ACROSS THE E CARIBBEAN. MEANWHILE...SURFACE HIGH PRESSURE CENTERED NW OF BERMUDA IS MAINTAINING 15-20 KT E WINDS PORTIONS OF THE E CARIBBEAN. ATLANTIC OCEAN... SCATTERED SHOWERS AND THUNDERSTORMS ARE OCCURRING S OF 24N BETWEEN 67W-80W...INCLUDING E CUBA...THE SE BAHAMAS...AND THE ADJACENT WATERS OF THE SW NORTH ATLC AS WELL AS HISPANIOLA. THIS ACTIVITY IS BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A 1011 MB SURFACE LOW NE OF CUBA NEAR 22N76W AND A TROUGH EXTENDING FROM 23N74W TO THE SURFACE LOW TO E CUBA NEAR 21N77W. THIS ACTIVITY IS ALSO BEING SUPPORTED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE OVER THE SW NORTH ATLC AND AN UPPER LEVEL TROUGH ACROSS THE CARIBBEAN. SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING THE NEXT DAY OR TWO AS IT MOVES GENERALLY NORTHWARD AT 10 TO 15 MPH. THE LOW IS FORECAST TO BE LOCATED NEAR 26N76W AS A 1010 MB LOW AT 19/1800 UTC. DURING THE NEXT 48 HOURS...THERE IS A LOW CHANCE...LESS THAN 30 PERCENT... OF THIS SYSTEM BECOMING A TROPICAL CYCLONE. IF NECESSARY...AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL INVESTIGATE THE SYSTEM ON TUESDAY. ALSO...THE PRESSURE GRADIENT AROUND THE LOW IS FORECAST TO RESULT IN GALE CONDITIONS N OF 27N W OF 75W TONIGHT THROUGH WEDNESDAY. ALSO ACROSS THE SW NORTH ATLC...THE DEEP LAYER TROUGH OVER THE E CONUS AND E GULF OF MEXICO IS SUPPORTING A COLD FRONT THAT EXTENDS FROM 32N77W TO 29N79W TO 28N80W. GALE CONDITIONS ARE FORECAST TO DEVELOP N OF THE FRONT BEGINNING AT 19/0000 UTC. LOW LEVEL CONVERGENCE NEAR THE COLD FRONT IS SUPPORTING SCATTERED SHOWERS AND THUNDERSTORMS OVER THE SW NORTH ATLC FROM 24N-30N W OF 75W...INCLUDING PORTIONS OF W CUBA...THE NW BAHAMAS AND THE CENTRAL AND S FLORIDA PENINSULA. E OF THE FRONT...A SURFACE RIDGE EXTENDS SOUTHWESTWARD FROM SURFACE HIGH PRESSURE CENTERED NW OF BERMUDA. SUBSIDENCE ASSOCIATED WITH THIS SURFACE RIDGE...AS WELL AS ATMOSPHERIC STABILITY ASSOCIATED WITH THE UPPER RIDGE OVER THE SW NORTH ATLC...ARE SUPPORTING GENERALLY FAIR WEATHER CONDITIONS. FARTHER TO THE E...AN OCCLUDED 1010 MB SURFACE LOW IS LOCATED NEAR 32N53W. AN ASSOCIATED SURFACE OCCLUDED FRONT EXTENDS FROM 32N46W TO 31N46W AND THEN SOUTHWESTWARD AS A STATIONARY FRONT FROM 31N46W TO 23N48W TO 19N56W TO 18N63W. LOW LEVEL CONVERGENCE IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ALONG AND WITHIN 120 NM E OF THE FRONTS. THIS SHOWER AND THUNDERSTORM ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE NEAR AN UPPER TROUGH THAT EXTENDS FROM AN UPPER LOW NEAR 32N51W TO 31N45W TO 27N42W. ACROSS THE E ATLC...A SURFACE RIDGE IS PRESENT WHERE MAINLY ZONAL FLOW ALOFT IS OCCURRING AND FAIR WEATHER CONDITIONS PERSIST. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS PRESENT S OF 13N E OF 58W WITH UPPER LEVEL HIGHS CENTERED NEAR 4N48W AND 5N27W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE UPPER LEVEL HIGHS AND UPPER LEVEL RIDGE IS ENHANCING THE CONVECTION ASSOCIATED WITH THE ITCZ AND WITH THE TROPICAL WAVE ALONG 45W/46W S OF 12N TO 2N. $$ COHEN