000 AXNT20 KNHC 181121 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SAT OCT 18 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...SPECIAL FEATURES... TROPICAL STORM OMAR IS CENTERED NEAR 32.9N 51.5W OR ABOUT 675 NM E OF BERMUDA AND ABOUT 1235 NM W OF THE AZORES AT 18/0900 UTC. ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB. MAXIMUM SUSTAINED WIND SPEED IS 50 KT WITH GUSTS TO 60 KT. PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT5/WTNT35 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS ON TROPICAL STORM OMAR. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 90 NM FROM THE CENTER. ISOLATED MODERATE CONVECTION IS FROM 24N-32N BETWEEN 44W-52W. TROPICAL STORM OMAR IS EXPECTED TO GRADUALLY WEAKEN DURING THE NEXT 48 HOURS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 33W/34W S OF 16N MOVING W 10-15 KT. THIS WAVE COINCIDES WITH A BROAD WESTWARD-MOVING DEEP LAYER MOISTURE SURGE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. COMPUTER MODEL GUIDANCE AND CIMSS WAVETRAK PRODUCT SHOW A DISTINCT MAXIMUM IN LOW LEVEL COUNTERCLOCKWISE CIRCULATION AROUND WAVE AXIS. SCATTERED MODERATE CONVECTION IS WITHIN 180 NM EITHER SIDE OF WAVE AXIS N OF 8N. A TROPICAL WAVE IS ALONG 53W/54W S OF 16N MOVING W 10-15 KT. THIS WAVE COINCIDES WITH A NORTH-TO-SOUTH DEEP LAYER MOISTURE MAXIMUM. SATELLITE IMAGERY DEPICTS BROAD INVERTED-V PATTERN IN CLOUD FIELD AROUND WAVE AXIS. ISOLATED MODERATE CONVECTION IS WITHIN 120 NM W OF WAVE AXIS S OF 13N...WHICH IS BEING ENHANCED BY THE ITCZ. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 8N12W 9N31W 8N46W 10N61W 10N82W. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL WAVES... SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 60 NM N AND 180 NM S OF AXIS BETWEEN 12W-18W. SCATTERED MODERATE CONVECTION IS WITHIN 210 NM N AND 150 NM S OF AXIS BETWEEN 18W-30W. ISOLATED MODERATE CONVECTION IS WITHIN 120 NM EITHER SIDE OF AXIS BETWEEN 41W-50W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 5N-9N BETWEEN 75W-78W...AFFECTING NW COLOMBIA. ...DISCUSSION... GULF OF MEXICO... AN UPPER TROUGH OVER THE E CONUS EXTENDS INTO THE CENTRAL AND W GULF...WITH SW TO W FLOW ALOFT COVERING MUCH OF THE GULF. THIS TROUGH IS SUPPORTING A COLD FRONT THAT IS DRAPED ACROSS THE N AND W GULF...EXTENDING FROM THE W FLORIDA PANHANDLE NEAR 30N84W TO 26N91W TO THE BAY OF CAMPECHE NEAR 19N95W. MID/UPPER-LEVEL MOISTURE EMBEDDED WITHIN THE FLOW ALOFT IS SUPPORTING CLOUDINESS AND ISOLATED SHOWERS WITHIN 120 NM N OF THE COLD FRONT N OF 24N. OVER THE SE GULF...DRY AIR EMBEDDED WITHIN WEAK DEEP LAYER FLOW IS RESULTING IN MAINLY FAIR WEATHER. GENERALLY STABLE ATMOSPHERIC CONDITIONS COVER MUCH OF THE BAY OF CAMPECHE UNDER AN UPPER HIGH CENTERED NEAR 19N92W. HOWEVER...WEAK UPPER DIFFLUENCE SE OF THE HIGH IS RESULTING IN ISOLATED MODERATE CONVECTION OVER THE SW YUCATAN PENINSULA...WHICH IS IMPACTING THE NEARBY WATERS OF THE BAY OF CAMPECHE. CARIBBEAN SEA... AN UPPER RIDGE EXTENDS FROM AN UPPER HIGH NEAR 22N55W TO NW VENEZUELA...AND A WEAK UPPER TROUGH IS PRESENT OVER THE NW CARIBBEAN. DRY AIR IN CONFLUENT UPPER FLOW BETWEEN THESE FEATURES IS LIMITING CONVECTION OVER A LARGE PART OF THE CARIBBEAN. HOWEVER...A SURFACE TROUGH EXTENDS FROM E GUATEMALA NEAR 15N89W TO A 1010 MB SURFACE LOW NEAR 17N88W TO 19N83W TO A 1011 MB SURFACE LOW NEAR 16N75W TO THE E CARIBBEAN NEAR 17N65W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS OCCURRING FROM 16N-19N BETWEEN 73W-76W IN RESPONSE TO LOW LEVEL CONVERGENCE NEAR THE 1011 MB LOW NEAR 16N75W. ALSO...LOW LEVEL CONVERGENCE IS GENERATING SCATTERED MODERATE/ISOLATED STRONG CONVECTION WITHIN 120 NM N AND ISOLATED MODERATE CONVECTION WITHIN 60 NM S OF THE SURFACE TROUGH BETWEEN 82W-88W...INCLUDING E PORTIONS OF THE YUCATAN PENINSULA AND E BELIZE. SCATTERED MODERATE CONVECTION OVER THE HIGHER TERRAIN OF NICARAGUA...COSTA RICA...AND NW VENEZUELA IS IMPACTING THE NEARBY CARIBBEAN WATERS. ATLANTIC OCEAN... PLEASE SEE SPECIAL FEATURES SECTION ABOVE FOR INFORMATION ON TROPICAL STORM OMAR. AN UPPER TROUGH OVER THE E CONUS IS BRINGING SW FLOW ALOFT TO THE W ATLC. HOWEVER...DRY AIR EMBEDDED WITHIN THE FLOW...COMBINED WITH STABLE CONDITIONS AROUND A 1018 MB SURFACE HIGH NEAR 30N71W...IS LIMITING CONVECTION OVER THE W ATLC. FURTHER TO THE E...AN UPPER HIGH IS CENTERED NEAR 22N55W...WITH MAINLY DRY AND STABLE CONDITIONS AROUND THIS HIGH. TO THE NE OF THIS HIGH...AN UPPER TROUGH ASSOCIATED WITH TROPICAL STORM OMAR IS N OF 28N BETWEEN 46W-52W...AND THE ASSOCIATED SURFACE TROUGH EXTENDS FROM 32N51W TO 26N51W TO 17N61W. ISOLATED SHOWERS ARE WITHIN 210 NM E OF THIS SURFACE TROUGH. FURTHER TO THE E...A 1026 MB SURFACE HIGH IS CENTERED NEAR 32N29W...AND A SURFACE RIDGE EXTENDS FROM THIS HIGH TO THE SW NEAR 21N49W...WHERE SUBSIDENCE AND STABLE CONDITIONS PREDOMINATE. WEAK INSTABILITY IN ASSOCIATION WITH AN UPPER TROUGH OVER THE E ATLC N OF 22N AND E OF 23W IS SUPPORTING ISOLATED SHOWERS WITHIN 120 NM OF 29N11W. OVER THE TROPICAL ATLC...AN UPPER RIDGE EXTENDS ALONG 13N BETWEEN W AFRICA AND 35W. TO THE W...A NE-TO-SW-TILTED UPPER TROUGH EXTENDS FROM 26N34W TO AN UPPER LOW NEAR 17N42W TO 8N46W...WHERE DEEP LAYER DRY AIR IS LIMITING CONVECTIVE DEVELOPMENT. $$ COHEN