000 AXNT20 KNHC 182349 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT MON SEP 18 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 HELENE WAS NEAR 23.9N 51.1W OR ABOUT 870 MILES EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS AT 18/2100 UTC. HELENE IS MOVING WEST-NORTHWEST 8 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 960 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 100 KT WITH GUSTS TO 120 KT. HELENE REMAINS A LARGE AND POWERFUL CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC ADVISORY UNDER MIATCPAT3/ WTNT33 KNHC FOR MORE DETAILS. NUMEROUS MODERATE TO STRONG CONVECTION IN A 60 NM-WIDE BAND EXTENDING WEST OF THE CENTER FROM 22N-25N. HELENE IS FORECAST TO REMAIN OUT TO SEA. THE CENTER OF HURRICANE GORDON WAS NEAR 37.9N 43.3W OR ABOUT 880 MILES WEST OF TERCEIRA IN THE AZORES AT 19/0000 UTC. GORDON IS MOVING QUICKLY TO EAST-NORTHEAST NEAR 24 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 975 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 80 KT WITH GUSTS TO 100 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. NUMEROUS MODERATE TO STRONG CONVECTION ARE WITHIN A 50 NM RADIUS OF THE CENTER. GORDON THREATENS THE AZORES. A TROPICAL STORM WATCH IS ALREADY IN EFFECT FOR THESE ISLANDS. THE TROPICAL CYCLONE WILL BE NEAR OR OVER THE AZORES ON TUESDAY AFTERNOON OR EVENING. ...TROPICAL WAVES... A SURFACE TROUGH...REMNANT OF THE FORMER SURFACE LOW THAT WAS NEAR THE CAPE VERDE ISLANDS YESTERDAY IS ALONG 28W FROM 18N TO 28N. SCATTERED SHOWERS AND TSTMS ARE JUST EAST OF THE TROUGH. A TROPICAL WAVE IS ALONG 36W SOUTH OF 20N. VIS SATELLITE IMAGERY SHOWS AN INVERTED V CLOUD PATTERN ASSOCIATED WITH THE WAVE. SCATTERED SHOWERS ARE ON THE SOUTHERN END OF THE WAVE. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 8N13W 7N30W 8N40W CURVING NORTHWARD TOWARD HURRICANE HELENE TO 12N45W. ANOTHER SEGMENT OF THE ITCZ IS FROM 12N48W TO 9N60W. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS WITHIN 80 NM MAINLY SOUTH OF THE AXIS BETWEEN 18W-28W AND BETWEEN 40W-46W. ...DISCUSSION... A DEEP LAYER TROUGH IS OVER CENTRAL U.S. AND NORTHERN MEXICO MOVING EWD. THE ASSOCIATED COLD FRONT EXTENDS FROM A 1010 MB SURFACE LOW PRES LOCATED OVER ARKANSAS ACROSS SE TEXAS INTO NORTHERN MEXICO. THIS SYSTEM IS FORECAST TO MOVE OFFSHORE THE TEXAS COAST THIS EVENING AND WILL EXTEND FROM THE FLORIDA PANHANDLE TO NE MEXICO ON TUESDAY. MODERATE N TO NE WINDS WILL FOLLOW THE FRONTAL BOUNDARY THAT IS EXPECTED TO MOVE ACROSS THE FLORIDA PENINSULA TUESDAY NIGHT/WEDNESDAY. MOISTURE AND THE CHANCE OF SHOWERS WILL INCREASE AHEAD OF THE FRONT. AS OF 2100 UTC...A PRE-FRONTAL TROUGH RUNS FROM 28N92W TO NEAR TAMPICO MEXICO. MUCH OF THE SHOWER ACTIVITY IS CURRENTLY BEHIND THIS TROUGH. AN UPPER ANTICYCLONE IS NEAR 28N92W COVERING THE EASTERN PORTION OF THE GULF. DRY AIR IS ON THE SOUTH SIDE OF THIS HIGH FROM 21N-27N BETWEEN 87W-93W. ANOTHER UPPER ANTICYCLONE IS SITUATED NEAR BELIZE AND COVERS SOUTH MEXICO AND THE YUCATAN PENINSULA. SCATTERED SHOWERS AND TSTMS HAVE DEVELOPED UNDER THE INFLUENCE OF THIS UPPER FEATURE. S TO SW WINDS OF 10-15 KT DOMINATES THE GULF AHEAD OF THE COLD FRONT. THE CARIBBEAN SEA... AN UPPER ANTICYCLONE IS NEAR BELIZE SUPPORTING THE DEVELOPMENT OF SCATTERED SHOWERS AND TSTMS OVER CENTRAL AMERICA AND THE YUCATAN PENINSULA. ANOTHER UPPER ANTICYCLONE IS LOCATED OVER THE LEEWARD ISLANDS WITH A RIDGE EXTENDING SOUTHWESTWARD ACROSS THE ABC ISLANDS. ABUNDANT DRY AIR...RESULTING IN MODERATE TO STRONG SUBSIDENCE DOMINATES THE EASTERN CARIBBEAN WEST OF 70W... INCLUDING PUERTO RICO AND DOMINICAN REPUBLIC AS WELL AS ALL THE LESSER ANTILLES. THE UW-CIMMS SAHARAN AIR LAYER IS STILL SHOWING THAT 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 75W. THE TRADE WINDS ARE ON THE WEAK SIDE...COMPARED WITH THE PREVIOUS DAYS THANKS TO THE TROPICAL CYCLONE ACTIVITY OVER THE ATLANTIC OCEAN THAT IS CREATING A BREAK IN THE SUBTROPICAL RIDGE. SCATTERED MODERATE CONVECTION IS FOUND OVER COSTA RICA AND PANAMA DUE TO THE CLOSE PROXIMITY OF THE ITCZ. CLUSTERS OF SCATTRED MODERATE TO ISOLATED STRONG CONVECTION HAVE ALSO DEVELOPED OVER NORTHERN VENZUELA AND COLOMBIA DUE TO A DIFFLUENT PATTERN ALOFT. THE ATLANTIC OCEAN... THE DEEP LAYER TROUGH LOCATED OVER THE W ATLC EXTENDS SOUTHWESTWARD ALONG THE NORTHERN BAHAMAS AND WESTERN CUBA TO THE NE PORTION OF THE YUCATAN PENINSULA. A SURFACE TROUGH RUNS ALONG 31N68W 24N74W 24N80W. SCATTERED SHOWERS AND TSTMS HAVE FORMED NEAR THE BASE OF THE UPPER TROUGH OVER THE FLORIDA KEYS...THE STRAIT OF FLORIDA AND ALONG CUBA. A MID TO UPPER LEVEL HIGH IS OVER THE LEEWARD ISLANDS WITH A RIDGE EXTENDING NWD ALONG 60/61W. DRY AIR COVERS THE ATLANTIC OCEAN AND THE CARIBBEAN SEA FROM 10N-27N BETWEEN 55W-70W. SATELLITE IMAGERY SHOWS THE OUTFLOW OF HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF LOW IS LOCATED NEAR 20N32W. 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 1023 MB HIGH ANCHORED NEAR 33N32W. THIS SYSTEM IS FORECAST TO MOVE SOUTH DURING THE NEXT 24 HOURS. $$ GR