000 AXNT20 KNHC 252355 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE SEP 25 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND THE 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. ...SPECIAL FEATURES... KAREN...THE ELEVENTH NAMED STORM OF THE 2007 HURRICANE SEASON DEVELOPED THIS MORNING IN THE EASTERN ATLANTIC. AT 25/2100 UTC THIS TROPICAL CYCLONE WAS NEAR 11.1N 39.9W OR ABOUT 1240 NM... 2305 KM...EAST OF THE WINDWARD ISLANDS...MOVING W-NW AT 13 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WINDS ARE 35 KT WITH GUSTS TO 45 KT. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. KAREN CONTINUES TO SHOW SOME BANDING FEATURES AND A WELL-DEFINED CIRCULATION ON VISIBLE IMAGES...BUT ITS PRESENTATION ON INFRARED IMAGERY IS NOT VERY IMPRESSIVE. THE SYSTEM CONTINUES TO LACK MUCH IN THE WAY OF CENTRAL DEEP CONVECTION AND...IN FACT...THE OVERALL AMOUNT OF DEEP CONVECTION IS MINIMAL. THE UPPER-LEVEL OUTFLOW OVER THE NORTHERN SEMICIRCLE HAS BECOME A LITTLE BETTER ESTABLISHED AND...IF KAREN DEVELOPS SOME MORE CENTRAL CONVECTION IT COULD STRENGTHEN SOME DURING THE NEXT COUPLE OF DAYS. THE OFFICIAL NHC FORECAST KEEPS KAREN AS A TROPICAL STORM DURING THE NEXT 5 DAYS. DATA FROM THE AIR FORCE RECONNAISSANCE AIRCRAFT SHOWS THAT THE AREA OF LOW PRESSURE IN THE SOUTHWESTERN GULF OF MEXICO HAS A WELL-DEFINED CIRCULATION...AND IS UPGRADED TO A TROPICAL DEPRESSION STATUS. AT 25/2215Z...TROPICAL DEPRESSION THIRTEEN WAS NEAR 21.7N 95.0W OR ABOUT 165 NM...305 KM...EAST OF TAMPICO MEXICO...MOVING TOWARD THE SW SLOWLY AT 3 KT. LITTLE OVERALL MOTION IS EXPECTED OVER THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1010 MB. MAXIMUM SUSTAINED WINDS ARE 25 KT WITH GUSTS TO 35 KT. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. THERE IS STILL SOME SOUTHWESTERLY SHEAR OVER THE CYCLONE ASSOCIATED WITH AN UPPER LOW ALONG THE MEXICAN COAST NEAR TAMPICO. THIS SHEAR IS EXPECTED TO RELAX AND BE REPLACED BY AN UPPER ANTICYCLONE OVER THE NEXT COUPLE OF DAYS...WHICH WOULD ALLOW THE SYSTEM AN OPPORTUNITY TO STRENGTHEN. AS A RESULT...THE DEPRESSION COULD BECOME A TROPICAL STORM ON WEDNESDAY. ...TROPICAL WAVES... A TROPICAL WAVE WAS ADDED TO THE 1800 UTC SURFACE MAP ALONG 19W S OF 18N BASED ON SURFACE DATA...SATELLITE IMAGERY AND AN EARLIER QUIKSCAT PASS THAT SHOWED THE WIND SHIFT ASSOCIATED WITH THE WAVE AXIS. IN ADDITION...THE WAVE SHOWS UP WELL IN THE LOW LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW CIMSS TPW PRODUCTS. MOST OF THE STRONG CONVECTION IS AHEAD OF THE WAVE AXIS...PROBABLY ASSOCIATED WITH A LOW EMBEDDED IN THE ITCZ. SCATTERED SHOWERS ARE WITHIN 130 NM EITHER SIDE OF WAVE APEX. A 1013 MB LOW PRESSURE AREA IS NEAR 17N63W ASSOCIATED WITH A TROPICAL WAVE ALONG 63W SOUTH OF 21N. CONVECTION HAS DIMINISHED NEAR THE LOW CENTER THIS EVENING. THE SYSTEM HAS CHANGED LITTLE IN ORGANIZATION AND UPPER-LEVEL WINDS HAVE BECOME LESS FAVORABLE FOR DEVELOPMENT. HOWEVER...THE LOW SHOULD MOVE TOWARD THE NORTHWEST...BRINGING SQUALLY WEATHER TO THE NORTHERN LEEWARD ISLANDS...THE UK/US VIRGIN ISLANDS AND PUERTO RICO DURING THE NEXT DAY OR SO. INTERESTS IN THESE AREAS SHOULD CONTINUE TO MONITOR THE PROGRESS OF THIS SYSTEM. SATELLITE IMAGERY DEPICTS SCATTERED MODERATE CONVECTION MAINLY EAST OF THE WAVE AXIS FROM 17N-21N BETWEEN 58W-63W. A WEAK TROPICAL WAVE IS ALONG 92W S OF 18N MOVING W 10-15 KT. WAVE REMAINS DIFFICULT TO LOCATE WITH ITS POSITION BASED MAINLY ON CONTINUITY FROM PREVIOUS ANALYSES. SCATTERED MODERATE CONVECTION IS MOSTLY INLAND NEAR THE GUATEMALA/MEXICO BORDER. FOR FUTURE INFO ON THIS WAVE PLEASE REFER TO PACIFIC DISCUSSION UNDER MIATWDEP. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 8N16W 6N24W 12N34W 5N46W 5N57W. CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION ARE FROM 4N-8N BETWEEN 22W-28W. DISCUSSION... GULF OF MEXICO... THE MAIN WEATHER FEATURE ACROSS THE GULF OF MEXICO IS NOW TROPICAL DEPRESSION THIRTEEN LOCATED IN THE SW PORTION OF THE AREA. SEE SPECIAL FEATURES ABOVE. A SURGE OF TROPICAL MOISTURE IS OVER THE BASIN MAINLY WEST OF 90W FROM THE BAY OF CAMPECHE ALL THE WAY NORTH TO LOUISIANA. UPPER DIFFLUENCE BETWEEN AN UPPER LOW NEAR TAMPICO AND AN UPPER RIDGE THAT CONTINUES TO DOMINATE MUCH OF THE CENTRAL GULF IS ENHANCING THIS SHOWER/TSTM ACTIVITY. VERY DRY MID TO UPPER AIR IS BEING ADVECTED INTO THE NE GULF AROUND AN UPPER TROUGH EXTENDING INTO THE AREA FROM THE WRN ATLC...WHILE AN AREA OF DISTURBED WEATHER PERSISTS OVER SOUTH FLORIDA...WEST-CENTRAL CUBA AND THE WESTERN BAHAMAS. THIS ACTIVITY IS PRIMARILY ASSOCIATED WITH A MID TO UPPER LEVEL TROUGH. SURFACES PRESSURES ARE NOT FALLING AT THIS TIME AND ADDITIONAL DEVELOPMENT...IF ANY WILL BE SLOW TO OCCUR. THIS SYSTEM COULD BRING LOCALLY HEAVY RAINS TO SOUTH FLORIDA AND THE KEYS DURING THE NEXT DAY OR TWO. AS OF 2100 UTC...A SFC TROUGH IS ANALYZED OVER THE AREA AND RUNS FROM 27N79W TO 23N83W. ELSEWHERE AT THE SFC...RIDGING EXTENDS INTO THE NE GULF AND SE U.S. AROUND A 1024 MB HIGH PRES CENTERED OVER THE W ATLC NEAR 37N70W. RIDGING WILL PERSIST OVER THE NRN GULF THROUGH WED WHILE LOW PRES MEANDERS IN THE SW PORTION. A WEAK COLD FRONT IS FORECAST TO MOVE OVER THE NORTHERN GULF WATERS THU NIGHT. CARIBBEAN SEA... THE MAIN WEATHER FEATURE IN THE CARIBBEAN IS ASSOCIATED WITH THE TROPICAL WAVE AND ASSOCIATED LOW PRESSURE AREA MOVING TOWARD THE NW. SEE TROPICAL WAVE SECTION. OTHERWISE THE BASIN IS FAIRLY TRANQUIL. AN UPPER RIDGE/TROUGH/RIDGE PATTERN CONTINUES TO DOMINATE THE AREA. CONVECTION HAS FLARED UP OVER DOMINICAN REPUBLIC AND ALONG THE COAST OF VENEZUELA THIS EVENING. THIS ACTIVITY SEEMS MOSTLY ASSOCIATED WITH DIFFLUENT FLOW ALOFT OVER THE AREA. UPPER SLY FLOW AHEAD OF AN UPPER TROUGH IS ADVECTING HIGH CLOUDS/MOISTURE NEWD OVER THE CENTRAL CARIBBEAN. THE COLOMBIAN LOW IS NEAR 10N67W GENERATING SOME SHOWER ACTIVITY. TRADES REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT WINDS/SEAS COULD BE HIGHER AT TIMES IN SQUALLS NEAR THE LOW/WAVE MOVING THROUGH THE EASTERN CARIBBEAN. ATLANTIC OCEAN... AN AREA OF DISTURBED WEATHER PERSISTS OVER SOUTH FLORIDA... WEST-CENTRAL CUBA AND THE WESTERN BAHAMAS. A CLOSED UPPER LOW OVER THE FLORIDA PENINSULA AND A SFC TROUGH THAT HAS DEVELOPED OVER SOUTH FLORIDA ARE CREATING THIS HUMID AND UNSTABLE WEATHER PATTERN. MORE DETAILS IN THE GULF OF MEXICO SECTION. ELSEWHERE AT THE SFC... A 1024 MB HIGH LOCATED N OF THE AREA IS PRODUCING AN ELY FLOW OVER THE W ATLC. A WEAK SFC TROUGH ENTERS THE FORECAST REGION NEAR 31N38W...THEN CONTINUES ALONG 28N50W TO 23N64W. SCATTERED SHOWERS ARE WITHIN 90 NM AHEAD OF THE TROUGH AXIS. ANOTHER WEAK TROUGH IS ALONG 52W WITH LIMITED SHOWER ACTIVITY. MODERATE RIDGING TAKES OVER IN THE E ATLC. THIS PATTERN IS STILL PRODUCING MODERATE TRADES IN THE E ATLC... EXCEPT STRONGER NEAR THE NW COAST OF AFRICA WHERE THE PRES GRADIENT TIGHTENS. IN THE MID AND UPPER LEVELS...A BROAD UPPER TROUGH EXTENDS MAINLY EAST TO WEST ALONG 29N/30N WEST OF 40W TO THE UPPER LOW LOCATED OVER FLORIDA. THIS TROUGH IS SUPPORTING THE SFC TROUGH MENTIONED ABOVE AND A COLD FRONT THAT IS CLIPPING THE AREA BETWEEN 50W-60W. ABUNDANT MID/TO UPPER LEVEL MOISTURE IS JUST SOUTH OF THE TROUGH AXIS. AN AMPLIFIED UPPER RIDGE IS SEEN E OF THE TROUGHING EXTENDING NE FROM AN UPPER HIGH SITUATED NEAR 21N38W TO BEYOND 32N33W. A LARGE UPPER LOW IS LOCATED E OF THE RIDGE BETWEEN THE MADEIRA/CANARY ISLANDS NEAR 31N19W. ISOLATED SHOWERS AREA NEAR THE LOW CENTER AND OVER THE CANARY ISLANDS. $$ GR