000 AXNT20 KNHC 181056 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1030 UTC. ...SPECIAL FEATURES... THE CENTER OF HURRICANE HELENE AT 18/0900 UTC WAS NEAR 22.3N 49.6W...OR ABOUT 800 NM EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS AND ABOUT 1005 NM EAST-SOUTHEAST OF BERMUDA. HELENE IS MOVING TOWARD THE NORTH-NORTHWEST AT 6 KT. A TURN TO THE WEST-NORTHWEST IS EXPECTED OVER THE NEXT 24 HOURS. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 958 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 105 KT WITH GUSTS TO 130 KT. HELENE IS A CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. SOME FURTHER STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS. 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/ISOLATED STRONG CONVECTION ASSOCIATED WITH HELENE IS FROM 21N-26W FROM 46W-52W. THE CENTER OF HURRICANE GORDON AT 18/0900 UTC WAS NEAR 36.5N 49.6W OR ABOUT 1080 NM WEST OF THE AZORES. GORDON IS MOVING TOWARD THE NORTHEAST AT 17 KT. A GRADUAL TURN TOWARD THE EAST-NORTHEAST WITH AN INCREASE IN FORWARD SPEED IS EXPECTED OVER THE NEXT 24 HOURS. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 983 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 70 KT WITH GUSTS TO 85 KT. LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT 24 HOURS. 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 ASSOCIATED WITH GORDON LIES FROM 35N-40N BETWEEN 46W-53W. ...TROPICAL WAVES... AN EASTERN ATLANTIC TROPICAL WAVE IS ALONG 24W/25W S OF 20N...MOVING W NEAR 10 KT. SATELLITE IMAGERY DEPICTS BROAD CYCLONIC TURNING OF THE LOW TO MID CLOUD FIELD ABOUT THE WAVE AXIS. A QUIKSCAT PASS AROUND 0800 UTC ALSO SHOWS THIS IS NOW LIKELY AN OPEN WAVE INSTEAD OF THE CLOSED LOW THAT HAS BEEN CARRIED THE PAST COUPLE DAYS. DEEP CONVECTION REMAINS MINIMAL WITH ONLY ISOLATED SHOWER/TSTM ACTIVITY NOTED WITHIN 200NM OF THE WAVE AXIS. A TROPICAL WAVE IS MOVING THROUGH THE YUCATAN PENINSULA AND CENTRAL AMERICA...AND THE EPAC ALONG 89W/90W S OF 22N MOVING W NEAR 15 KT. CONVECTION OVER CENTRAL AMERICA HAS DIMINISHED OVER THE LAST FEW HOURS. PATCHES OF SCATTERED MODERATE CONVECTION NOTED IN THE EPAC FROM 11N-14N BETWEEN 86W-94W. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N11W 11N24W 10N29W 11N44W 13N49W 10N61W...AND IN THE SOUTHERN CARIBBEAN NEAR 9N77W TO INLAND OVER CENTRAL AMERICA NEAR 9N83W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE INLAND OVER AFRICA AND OVER THE ADJACENT ERN ATLC WATERS FROM 6N-15N BETWEEN 12W-33W. THESE CLUSTERS ARE NOT AS IMPRESSIVE AS THEY WERE LAST NIGHT. SCATTERED MODERATE ALSO FROM 9N-12N BETWEEN 51W-55W. A CLUSTER OF NUMEROUS MODERATE/ISOLATED STRONG CONVECTION IS MOVING INTO THE SW CARIBBEAN OFF THE COLOMBIAN COAST FROM 9N-13N BETWEEN 74W-79W. ISOLATED SHOWERS AND TSTMS ARE NOTED ELSEWHERE WITHIN 200NM OF THE ITCZ. ...DISCUSSION... THE GULF OF MEXICO... THE MOST ACTIVE WEATHER IN THE GULF TONIGHT IS ASSOCIATED WITH PREFRONTAL INSTABILITY OVER COASTAL TEXAS AND THE ADJACENT GULF WATERS. BROWNSVILLE AND CORPUS CHRISTI RADAR IMAGERY SHOW NUMEROUS SHOWERS AND TSTMS MOVING INTO THE NW GULF. A MID TO UPPER LEVEL ANTICYCLONE IS OVER THE NRN GULF...WITH A CENTER ESTIMATED BY WV IMAGERY NEAR 27N90W. THERE IS A SMALL UPPER LOW SEEN SPINNING IN THE SW GULF NEAR 22N97W. OVERALL ABUNDANT DRY MID TO UPPER LEVEL AIR AND FAIR WEATHER IS OVER THE MIDDLE AND SOUTHERN GULF FROM 19N-26N BETWEEN 82W-98W. THERE ARE ALSO ISOLATED SHOWERS AND TSTMS SEEN IN THE SE GULF JUST OFF SW FLORIDA. THIS IS ASSOCIATED WITH UPPER DIFFLUENT AIR BETWEEN THE UPPER HIGH S OF LOUISIANA AND THE TROUGHING OFF THE EAST COAST...ALONG WITH A SURFACE TROUGH/OLD COLD FRONT BOUNDARY EXTENDING THROUGH THE FLORIDA STRAITS. THE REMAINDER OF THE SURFACE PATTERN IS DOMINATED BY ANTICYCLONIC 10-15KT SE FLOW...EXCEPT STRONGER/GUSTY WINDS IN THE NW GULF WITH CONVECTION. THE CARIBBEAN SEA... A PAIR OF MID TO UPPER LEVEL ANTICYCLONES ARE OVER THE NW CARIBBEAN NEAR 18N86W AND 17N77W. THE ONLY DEEP CONVECTION SEEN IN THE CARIBBEAN IS IN THE SW PORTION MOVING W FROM COLOMBIA. THIS SEEMS MOST ASSOCIATED WITH THE ITCZ AS DESCRIBED ABOVE. THERE IS A LITTLE UPPER LEVEL MOISTURE BEING ADVECTED N FROM SOUTH AMERICA INTO THE FAR SRN CARIBBEAN...AROUND AN UPPER TROUGH EXTENDING NNE THROUGH COLOMBIA TOWARDS HISPANIOLA AND THE UPPER HIGH JUST NE OF THE LEEWARD ISLANDS. OVERALL THOUGH...MUCH OF THE REMAINDER OF THE CARIBBEAN BETWEEN 60W-80W IS DOMINATED BY VERY DRY MID TO UPPER LEVEL AIR AND FAIR WEATHER...ALONG WITH FAIRLY DENSE SAHARAN DUST AS DEPICTED BY THE UW-CIMMS SAHARAN AIR LAYER ANALYSIS. 10-20 KT TRADES PERSIST AT THE SURFACE. THE ATLANTIC OCEAN... THE DEEP LAYER TROUGH LOCATED OFF THE U.S. EAST COAST EXTENDS SOUTHWESTWARD ALONG THE NORTHERN BAHAMAS AND ENDS NEAR WESTERN CUBA. ASSOCIATED SURFACE TROUGH/OLD COLD FRONT BOUNDARY RUNS FROM 24N81W TO 30N68W...AND ATTACHES TO A 1004MB SURFACE LOW SPINNING ABOUT 300NM E OF CAPE HATTERAS. ISOLATED SHOWERS AND TSTMS ASSOCIATED WITH THIS BOUNDARY ARE NOW MOSTLY LIMITED TO THE FLORIDA STRAITS AND SRN BAHAMAS. A MID TO UPPER LEVEL HIGH IS JUST NE OF THE LEEWARD ISLANDS NEAR 19N62W. SATELLITE IMAGERY AND GOES HIGH DENSITY WINDS SHOW DISTINCT OUTFLOW OF HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF MID TO UPPER LEVEL LOW IS LOCATED NEAR 20N32W. EAST OF THE LOW THERE IS AN UPPER ANTICYCLONE COVERING WESTERN AFRICA AND THE FAR EAST ATLANTIC OCEAN. ELSEWHERE AT THE SURFACE...A RIDGE DOMINATES THE E ATLC FROM A 1024 MB HIGH ANCHORED WITHIN AROUND 100 NM WNW OF THE MADEIRA ISLANDS...WITH ANOTHER 1024MB CENTER FURTHER W NEAR 33N35W. $$ WILLIS