000 AXNT20 KNHC 180047 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SUN SEP 17 2006 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN 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...WEATHER OBSERVATIONS...RADAR... AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...SPECIAL FEATURES... THE CENTER OF HURRICANE GORDON WAS NEAR 34.6N 52.4W OR ABOUT OR ABOUT 1430 MILES WEST OF THE AZORES AT 17/2100. GORDON IS MOVING TOWARD THE NORTH-NORTHEAST AT 12 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 983 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 70 KT WITH GUSTS TO 85 KT. PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC OR THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. SCATTERED MODERATE CONVECTION IS ASSOCIATED WITH GORDON MAINLY NORTH OF THE CENTER FROM 34N-37N BETWEEN 50W-53W. GORDON IS EXPECTED TO BECOME EXTRATROPICAL IN ABOUT TWO DAYS NEAR THE AZORES AS IT MERGES WITH A FRONTAL SYSTEM. THE CENTER OF HURRICANE HELENE WAS NEAR 21.2N 49.3W...OR ABOUT 920 NM EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS AT 2100 UTC. HELENE IS MOVING NORTHWEST 8 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 970 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 90 KT WITH GUSTS TO 110 KT. PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC ADVISORY UNDER MIATCPAT2/ WTNT32 KNHC FOR MORE DETAILS. A BAND OF MODERATE TO STRONG CONVECTION IS MAINLY ON THE WESTERN SIDE OF THE HURRICANE FROM 19N-23N BETWEEN 48W-51W. SOME STRENGTHENING IS POSSIBLE DURING THE NEXT 24-36 HOURS AND HELENE MAY BECOME THE SECOND MAJOR HURRICANE OF THE SEASON. ...TROPICAL WAVES... AN ATLANTIC OCEAN 1012 MB LOW PRESSURE CENTER IS NEAR 18N23W...JUST NORTH OF THE CAPE VERDE ISLANDS. SHOWER ACTIVITY ASSOCIATED WITH THIS BROAD AREA OF LOW PRESSURE HAS DIMINISHED AND PROBABLY ONLY AN OPEN WAVE LEFT IN THIS AREA. BASED ON THAT...A TROPICAL WAVE WAS ADDED ALONG 22/23W ON THE 1800 UTC MAP. AS OF 2100 UTC...A TROPICAL WAVE IS ENTERING THE YUCATAN PENINSULA. IT AXIS LIES ALONG 87/88W. THE WAVE IS ENHANCING THE SHOWER/TSTM ACTIVITY OVER NICARAGUA...HONDURAS...THE YUCATAN PENINSULA AND NORTHERN GUATEMALA. THERE ARE ALSO SCATTERED SHOWERS OVER THE NW CARIBBEAN CARIBBEAN JUST BEHIND THE WAVE AXIS. THE NORTHERN END OF A TROPICAL WAVE IS MOVING THROUGH SOUTHERN MEXICO...NOW OVER THE AREA JUST WEST OF THE ISTHMUS OF TEHUANTEPEC. SCATTERED SHOWERS AND TSTMS ARE OVER CHIAPAS AND OAXACA IN MEXICO NEAR THE WAVE AXIS. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N12W 12N21W 10N30W 12N44W 13N48W 10N60W. CLUSTERS OF SCATTERED MODERATE/STRONG CONVECTION ARE INLAND JUST NORTH OF THE ITCZ BETWEEN 11W-17W. SIMILAR CONVECTION IS FOUND FROM 6N-10N BETWEEN 18W-20W. ...DISCUSSION... THE GULF OF MEXICO... AN UPPER RIDGE COVERS THE ENTIRE GULF AND THE SE U.S. INCLUDING THE STATE OF FLORIDA. ABUNDANT DRY MID TO UPPER LEVEL AIR COVERS THE AREA. THERE ARE ISOLATED SHOWERS OVER THE NORTHERN GULF WATERS N OF 27N AND WEST OF 85W. SCATTRED SHOWERS AND TSTMS ARE ALSO ALONG THE FLORIDA WEST COAST MAINLY SOUTH OF TAMPA BAY. A DIFFLUENT PATTERN ALOFT BETWEEN THE RIDGE OVER THE GULF AND A TROUGH OFF THE U.S. EAST COAST IS ENHANCING THIS SHOWER ACTIVITY. AT THE SURFACE...SELY WINDS OF 10-15 KT DOMINATES THE GULF AHEAD OF A NEW COLD FRONT THAT IS EXPECTED TO MOVE IN LATE MON AFTERNOON OR EARLY EVENING...INCREASING THE LIKELIHOOD OF SHOWERS OVER THE NORTHERN GULF WATERS. THE CARIBBEAN SEA... AN UPPER ANTICYCLONE IS OVER THE NW CARIBBEAN NEAR 17N83W SUPPORTING THE DEVELOPMENT OF CONVECTIVE ACTIVITY OVER CENTRAL AMERICA AND THE SW CORNER OF THE AREA. ANOTHER UPPER ANTICYCLONE IS SITUATED JUST EAST OF THE LESSER ANTILLES. ABUNDANT DRY AIR...RESULTING IN MODERATE TO STRONG SUBSIDENCE DOMINATES THE EASTERN CARIBBEAN INCLUDING PUERTO RICO AND DOMINICAN REPUBLIC AS WELL AS THE LESSER ANTILLES. THE UW-CIMMS SAHARAN AIR LAYER ANALYSIS ALSO SUGGESTS THIS AREA IS UNDER THE INFLUENCE OF SAHARAN DUST. UPPER LEVEL MOISTURE IS BEING ADVECTED OVER VENEZUELA. AN INVERTED TROUGH LIES BETWEEN THESE TWO ANTICYCLONES ALONG 71W. MODERATE TO STRONG WINDS ARE BLOWING ACROSS THE BASIN. THE STRONGEST WINDS OF 2O KT ARE SEEN JUST NORTH OF WESTERN VENEZUELA AND NORTHERN COLOMBIA. SCATTERED MODERATE CONVECTION OVER THE SW CORNER OF THE AREA AND OVER COSTA RICA AND PANAMA DUE TO THE CLOSE PROXIMITY OF THE ITCZ. THE ATLANTIC OCEAN... THE DEEP LAYER TROUGH LOCATED OFF THE U.S. EAST COAST EXTENDS SOUTHWESTWARD ALONG THE NORTHERN BAHAMAS AND WESTERN CUBA. A SURFACE TROUGH RUNS FROM 26N72W TO 24N80W. SHOWERS AND TSTMS HAVE FORMED ALONG CUBA JUST EAST OF THIS UPPER TROUGH. THE ASSOCIATED FRONTAL SYSTEM IS A WEAKENING COLD FRONT THAT EXTENDS FROM A 1008 MB LOW PRESSURE LOCATED NORTH OF THE AREA NEAR 35N70W TO 26N72W. ISOLATED SHOWERS ARE RELATED TO THE FRONTAL BOUNDARY. A MID TO UPPER LEVEL HIGH IS EAST OF THE LEEWARD ISLANDS NEAR 15N58W. SATELLITE IMAGERY SHOWS THE OUTFLOW OF HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF LOW IS LOCATED NEAR 23N31W. EAST OF THE LOW THERE IS AN UPPER ANTICYCLONE COVERING WESTERN AFRICA AND THE FARTHER EAST ATLANTIC OCEAN. AT THE SURFACE...A RIDGE DOMINATES THE E ATLC FROM A 1024 MB HIGH ANCHORED WITHIN AROUND 200 NM NORTH OF MADEIRA ISLANDS. ISOLATED TO SCATTERED SHOWERS ARE NORTH OF 22N AND EAST OF 25W...JUST EAST OF THE UPPER TROUGH AXIS MENTIONED ABOVE. $$ GR