000 AXNT20 KNHC 162358 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE SEP 16 2008 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 2315 UTC. ...TROPICAL WAVES... A NEW TROPICAL WAVE IS ADDED TO THE 18Z ANALYSIS/SURFACE MAP ALONG 17W/18W BASED ON SURFACE OBSERVATIONS AND SATELLITE PICTURES. THIS WAVE IS CURRENTLY MOVING OFF THE AFRICAN COAST. A BROAD CYCLONIC TURNING IS OBSERVED ALONG THE WAVE AXIS FROM 10N-14N. SATELLITE DERIVED WINDS AND 850 MB VORTICITY ALSO SUPPORT THE WAVE POSITION INDICATED. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS INLAND JUST BEHIND THE WAVE AXIS FROM 11N-19N. A LOW AMPLITUDE TROPICAL WAVE IS ALONG 36W/37W SOUTH OF 13N MOVING WEST NEAR 10 KT. SCATTERED SHOWERS ARE NEAR THE INTERSECTION OF THE WAVE AXIS AND THE ITCZ. PATCHES OF LOW LEVEL CLOUDS ARE NEAR THE NORTHERN END OF THE WAVE LINE. A TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 61W/62W SOUTH OF 21N MOVING WEST NEAR 10 KT. THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMMS DEPICTS ENHANCED DEEP LAYER MOISTURE JUST EAST OF THE WAVE AXIS. A SWIRL OF LOW CLOUDS LOCATED NEAR 21N61W IS MOVING IN TANDEM WITH THIS TROPICAL WAVE. A LARGE AREA OF SCATTERED MODERATE CONVECTION IS WITHIN 200 NM E OF THE WAVE AXIS. A DIFFLUENT PATTERN ALOFT IS HELPING TO INDUCE THIS ACTIVITY. ANOTHER TROPICAL WAVE IS OVER THE CARIBBEAN SEA EXTENDING FROM JAMAICA TO EASTERN PANAMA ALONG 78W SOUTH OF 20N MOVING WEST 10-15 KT. THE WAVE IS GENERATING SCATTERED MODERATE CONVECTION OVER THE CENTRAL CARIBBEAN JUST SOUTH OF JAMAICA. A TROPICAL WAVE EXTENDS ACROSS THE YUCATAN PENINSULA AND BELIZE CROSSING EL SALVADOR INTO THE EPAC. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE WAVE AXIS OVER THE YUCATAN PENINSULA AND CENTRAL AMERICA...PARTICULARLY ACROSS BELIZE. VISIBLE SATELLITE IMAGERY DEPICTS SOME INVERTED-V STRUCTURE IN THE CLOUD PATTERN ASSOCIATED WITH THIS WAVE. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 10N15W 8N25W 8N35W 9N45W 10N60W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 8N-11N BETWEEN 21W-25W. SIMILAR CONVECTION IS ALSO SEEN WITHIN 100 NM N OF THE AXIS BETWEEN 46W-56W. ...DISCUSSION... GULF OF MEXICO... A WEAKENING COLD FRONT EXTENDS FROM THE APALACHEE BAY WWD TO THE CENTRAL GULF...AND THEN CURVES SOUTHWARD TOWARD THE WESTERN PORTION OF THE BAY OF CAMPECHE ENTERING MEXICO JUST SOUTH OF VERACRUZ WHICH IS REPORTING GUSTY WINDS OF 25 KT FROM THE NW. NORTH TO NORTHEASTERLY SURFACE WINDS...WITH SPEEDS UP TO 25 KT PER A RECENT ASCAT PASS ARE BLOWING BEHIND THE COLD FRONT...WITH MORE EASTERLY WINDS AHEAD OF THE FRONT. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS CONTINUE TO DEVELOP IN THE VICINITY OF THE FRONTAL BOUNDARY...ESPECIALLY BETWEEN 92W AND THE MEXICAN COAST. THIS CONVECTIVE ACTIVITY IS IN RESPONSE TO WEAK UPPER LEVEL DIFFLUENCE ASSOCIATED WITH AN UPPER LEVEL ANTICYCLONE LOCATED OVER N-CENTRAL MEXICO. WEAK SURFACE RIDGE DOMINATES THE REMAINDER OF THE GULF REGION AHEAD OF THE COLD FRONT. THIS WEATHER PATTERN IS SUPPORTING LIGHT EASTERLY WINDS GENERALLY UNDER 10 KT. AN UPPER-LEVEL TROUGH EXTENDS FROM N FLORIDA TO THE YUCATAN PENINSULA. SWLY FLOW AHEAD OF THIS UPPER FEATURE IS ENHANCING CONVECTION ASSOCIATED WITH THE TROPICAL WAVE OVER THE YUCATAN PENINSULA...AND IS ALSO SUPPORTING SOME CLOUDINESS OVER THE SE PORTION OF THE GULF. THE AFOREMENTIONED FRONT WILL CONTINUE TO WEAKEN AND BECOME DIFFUSE ON THU. ACCORDING TO THE COMPUTER MODELS...A WEAK LOW PRES IS FORECAST TO PERSIST OVER THE NW CORNER OF THE GULF THU AND FRI BUT DISSIPATE SAT. CARIBBEAN SEA... THERE ARE THREE TROPICAL WAVES BETWEEN THE LESSER ANTILLES AND THE YUCATAN PENINSULA. SEE TROPICAL WAVE SECTION FOR DETAILS. AN AREA OF MODERATE TO ISOLATED STRONG CONVECTION PERSISTS OVER THE SW CARIBBEAN JUST EAST OF THE CARIBBEAN PLAINS OF NICARAGUA. THIS SHOWER/TSTM ACTIVITY IS ALSO AFFECTING COSTA RICA AND WESTERN PANAMA...AND EXTENDS INTO THE EPAC. SOME OF THE COMPUTER MODELS LIKE THIS AREA OF CONVECTION AND THE GFS TRIES TO DEVELOP A TROPICAL CYCLONE NEAR THE PACIFIC COASTLINE OF CENTRAL AMERICA LATE THIS WORK WEEK. CLUSTERS OF MODERATE TO STRONG CONVECTION ARE AFFECTING WESTERN VENEZUELA AND N COLOMBIA. SHOWERS AND TSTMS ARE FIRED UP OVER HISPANIOLA. UPPER DIFFLUENCE ASSOCIATED WITH AN UPPER-LEVEL LOW SPINNING JUST SOUTH OF PUERTO RICO IS ASSISTING IN THE DEVELOPMENT OF THIS ACTIVITY. AN UPPER-LEVEL HIGH CENTERED NEAR CABO GRACIAS A DIOS DOMINATES THE WESTERN CARIBBEAN. EASTERLY SURFACE TRADE WINDS AT 15 TO 20 KT ARE BLOWING ACROSS MUCH OF THE BASIN. ATLANTIC OCEAN... WEAK PRES GRADIENT CONTINUES TO DOMINATES THE W ATLC DUE TO THE PRESENCE OF A WEAK SFC TROUGH THAT ENTERS THE AREA NEAR 31N62W THEN CONTINUES SW TO THE SE BAHAMAS NEAR 23N73W. SCATTERED SHOWERS ARE WITHIN 60 NM OF TROUGH. JUST E OF THE TROUGH...THERE IS AN AREA OF MODERATE CONVECTION AND COVERS FROM 26N-31N BETWEEN 57W-61W. THIS TROUGH SEEMS TO BE A REFLECTION OF AN UPPER-LEVEL TROUGH EXTENDING FROM AN UPPER-LEVEL LOW NEAR 30N63W TO A SECOND UPPER-LEVEL LOW LOCATED JUST SOUTH OF PUERTO RICO. THE SURFACE TROUGH IS EXPECTED TO SLIDE NORTHWESTWARD OVER THE NEXT DAY OR SO...WITH CONVECTION REMAINING POSSIBLE EAST OF THE TROUGH. A SFC RIDGE ANCHORED ON A HIGH SITUATED WELL N OF THE FORECAST AREA ENVELOPS THE CENTRAL AND EASTERN ATLC RESULTING IN MOSTLY FAIR WEATHER ACROSS THE AREA. A SWIRL OF LOW CLOUDS IS NOTED ON SATELLITE IMAGERY RELATED TO A 1013 MB SFC LOW LOCATED NEAR 18N38W. THIS LOW IS EXPECTED TO MOVE WEST-SOUTHWESTWARD DURING THE NEXT 24 HOURS. NO SUBSTANTIAL CONVECTION HAS BEEN OBSERVED WITH THIS LOW THUS FAR...AS THIS FEATURE REMAINS EMBEDDED WITHIN A DEEP-LAYER RIDGE THAT COVERS MUCH OF THE TROPICAL ATLC. $$ GR