000 AXNT20 KNHC 141040 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT TUE JUL 14 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 33W/34W S OF 18N MOVING W NEAR 20 KT. THIS WAVE COINCIDES WITH A LOW AMPLITUDE MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SATELLITE-DERIVED WINDS INDICATE CYCLONIC CURVATURE IN THE FLOW WITHIN THE 800-600 MB LAYER. THE QUIKSCAT PASS AROUND 13/2015 UTC INDICATED E WINDS AT 10-15 KT AHEAD OF THE WAVE FOLLOWED BY E TO SE WINDS AT 15-20 KT BEHIND THE WAVE. THIS WAVE IS ASSOCIATED WITH SCATTERED MODERATE CONVECTION FROM 9N-13N BETWEEN 33W-37W. A TROPICAL WAVE IS E OF THE LESSER ANTILLES AND EXTENDS FROM 24N59W TO 14N58W TO 6N54W MOVING W NEAR 20 KT. THE STRONG LOW LEVEL EASTERLY JET FOLLOWING THE N PORTION OF THE WAVE IS CONTRIBUTING TO THE NW-SE TILT OF THE WAVE. A WELL-DEFINED AND HIGHLY-AMPLIFIED INVERTED-V PATTERN IS EVIDENT IN THE COVERAGE OF LOW-LEVEL CLOUDS BASED ON RECENT SATELLITE IMAGERY... COINCIDING WITH A MAXIMUM IN TOTAL PRECIPITABLE WATER. THE RELATIVELY SHORT WAVELENGTH OF THE TROPICAL WAVE IS CURRENTLY PRECLUDING AN EVEN FASTER WESTWARD WAVE MOTION. THE WAVE IS LEADING ABUNDANT DRY LOW/MID-LEVEL SAHARAN AIR. THIS IS CONTRIBUTING TO A DENSITY DIFFERENCE SUFFICIENT TO PROVIDE LOW LEVEL ATMOSPHERIC LIFT SUPPORTING RECENT DEVELOPMENT OF SCATTERED MODERATE CONVECTION ALONG AND WITHIN 60 NM E OF THE WAVE AXIS. THIS IS PARTICULARLY THE CASE N OF 16N...WHICH IS IN A ZONE OF UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE W OF THE WAVE AND AN UPPER LEVEL TROUGH E OF THE WAVE. THE DRY AIR IS LIKELY CONTRIBUTING TO STRONG DOWNDRAFTS AND GUSTY OUTFLOW WINDS WITH THIS CONVECTION. THE GFS APPEARS TO HAVE A GOOD HANDLE ON THIS FEATURE AND SHOWS IT MOVING INTO THE LESSER ANTILLES DURING THE NEXT DAY. A TROPICAL WAVE IS ALONG 92W S OF 19N MOVING W 15-20 KT. THE WAVE POSITION IS MAINLY BASED ON A MOISTURE MAXIMUM IN TOTAL PRECIPITABLE WATER AS FEW ADDITIONAL SIGNATURES ARE APPARENT IN SATELLITE IMAGERY OR OBSERVATIONS. SCATTERED MODERATE CONVECTION IS OVER SE MEXICO FROM 16N-18N BETWEEN 94W-96W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 12N16W 11N27W 10N38W 8N48W 8N61W. SCATTERED MODERATE TO STRONG CONVECTION IS FROM 7N-13N BETWEEN 18W-22W. SCATTERED MODERATE CONVECTION IS FROM 7N-10N BETWEEN 25W-32W. SCATTERED MODERATE CONVECTION IS ALSO FROM 8N-11N BETWEEN 42W-51W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL RIDGE EXTENDS SOUTHEASTWARD INTO THE GULF OF MEXICO AND IS ASSOCIATED WITH A SURFACE RIDGE ALONG 26N AND A 1018 MB SURFACE HIGH NEAR 25N84W. GENERALLY FAIR WEATHER IS PRESENT ACROSS THE GULF. ONE EXCEPTION IS OVER THE N CENTRAL GULF...WHERE SCATTERED SHOWERS AND THUNDERSTORMS ARE PRESENT N OF 28N BETWEEN 87W-90W. THIS ACTIVITY IS BEING SUPPORTED BY ATMOSPHERIC LIFT ASSOCIATED WITH A WEAK SHORTWAVE TRANSLATING SOUTHEASTWARD ON THE OUTER PERIPHERY OF THE AFOREMENTIONED UPPER RIDGE. WINDS ARE LIGHT AND VARIABLE IN THE VICINITY OF THE SURFACE RIDGE ACROSS THE N GULF...WITH ANTICYCLONIC FLOW AROUND THE RIDGE SUPPORTING A BROAD SWATH OF E WINDS OF 10-15 KT ACROSS THE S HALF OF THE GULF. LITTLE CHANGE IS EXPECTED OVER THE NEXT DAY OR TWO AS BOTH THE UPPER AND SFC RIDGE REMAIN IN PLACE. CARIBBEAN SEA... FRESH TO STRONG TRADE WINDS ARE OCCURRING BETWEEN THE SUBTROPICAL RIDGE OVER THE CENTRAL ATLC AND A BROAD TROUGH OVER NORTHERN SOUTH AMERICA...WITH THE STRONGEST FLOW NEAR THE COAST OF COLOMBIA. THESE WINDS WILL REMAIN STRONG OVER THE NEXT SEVERAL DAYS AS THE SUBTROPICAL RIDGE REMAINS IN PLACE AND A TROPICAL WAVE MOVES INTO THE AREA. IN FACT...GALE CONDITIONS ARE FORECAST FOR THE LATTER HALF OF THIS WEEK...AS THE LOW LEVEL FLOW STRENGTHENS ACROSS THE CARIBBEAN. ALOFT...INSTABILITY ASSOCIATED WITH AN UPPER LEVEL LOW OVER THE N CENTRAL CARIBBEAN CENTERED NEAR 18N79W IS RESULTING IN SCATTERED SHOWERS AND THUNDERSTORMS N OF 16N BETWEEN 75W-82W INCLUDING PORTIONS OF JAMAICA AND CUBA. DEEP LAYER DRY AIR IS RESULTING IN GENERALLY FAIR WEATHER ACROSS THE E CARIBBEAN. A TROPICAL WAVE IS FORECAST TO ENTER THE CARIBBEAN LATER TODAY. THE WAVE WILL BE ACCOMPANIED BY...AND FOLLOWED BY...STRONGER WINDS AND A STRONG SURGE OF SAHARAN AIR...WHICH WILL LIMIT THE AREAL COVERAGE OF DEEP CONVECTION NEAR THE WAVE...BUT WILL ALSO INCREASE THE THREAT FOR STRONGER DOWNDRAFTS AND GUSTY OUTFLOW WINDS WITH ANY CONVECTION THAT DEVELOPS. ATLANTIC OCEAN... DEEP LAYER MOISTURE IS COMBINING WITH UPPER LEVEL DIFFLUENCE IN NORTHWESTERLY FLOW ALOFT TO RESULT IN SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE SW NORTH ATLC N OF 26N W OF 77W...INCLUDING PORTIONS OF THE NW BAHAMAS. ALSO...SCATTERED SHOWERS AND ISOLATED TSTMS ARE N OF 24N BETWEEN 64W-71W. THIS ACTIVITY IS BEING SUPPORTED BY LOW LEVEL CONVERGENCE NEAR A SURFACE TROUGH EXTENDING FROM 28N67W TO 24N72W. THIS ACTIVITY IS ALSO SUPPORTED BY ATMOSPHERIC INSTABILITY ASSOCIATED WITH AN UPPER TROUGH OVER THE SW NORTH ATLC. SUBSIDENCE AND GENERALLY FAIR WEATHER ARE PRESENT ACROSS MUCH OF THE CENTRAL AND E ATLC AROUND A BROAD SURFACE RIDGE WITH A 1031 MB HIGH NEAR 34N47W. A SURFACE TROUGH FROM 31N32W TO 28N37W...THOUGH ASSOCIATED CLOUDINESS AND SHOWERS ARE SHALLOW IN NATURE AND LIMITED TO LOCATIONS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. ACROSS THE TROPICAL N ATLC...AN UPPER LEVEL RIDGE IS ALONG 14N E OF 39W AND AN UPPER LEVEL HIGH IS CENTERED NEAR 14N30W...WITH ASSOCIATED UPPER LEVEL DIVERGENCE ENHANCING THE CONVECTION NEAR THE ITCZ. $$ COHEN