000 AXNT20 KNHC 171053 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...SPECIAL FEATURES... HURRICANE GORDON WAS CENTERED NEAR 32.6N 53.3W OR ABOUT 580 NM EAST OF BERMUDA AT 17/0900 UTC MOVING NORTH NEAR 5 KT. A TURN TOWARD THE NORTHEAST WITH A GRADUAL INCREASE IN FORWARD SPEED IS EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 987 MB. MAXIMUM SUSTAINED WINDS ARE 65 KT WITH GUSTS TO 80 KT. SOME SLOW WEAKENING IS FORECAST DURING THE NEXT 24 HOURS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. SCATTERED MODERATE CONVECTION ASSOCIATED WITH GORDON LIES FROM 31N-35N BETWEEN 51W-55W. HURRICANE HELENE WAS CENTERED NEAR 20.0N 48.2W OR ABOUT 850 NM EAST OF THE NORTHERN LEEWARD ISLANDS AT 17/0900 UTC MOVING NORTHWEST AT 8 KT. A MOTION BETWEEN WEST-NORTHWEST AND NORTHWEST IS EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 979 MB. MAXIMUM SUSTAINED WINDS ARE 75 KT WITH GUSTS TO 90 KT. SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS MODERATE/ISOLATED STRONG CONVECTION ASSOCIATED WITH HELENE LIES FROM 18N-24N BETWEEN 45W-50W. ...TROPICAL WAVES... A BROAD 1012MB LOW NEAR 17N22W...MOVING WNW 5-10 KT...IS NEAR THE EASTERN CAPE VERDE ISLANDS BUT DEEP CONVECTION REMAINS MINIMAL OVERALL. THERE IS A SMALL CLUSTER OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION N OF THE LOW FROM 19N-20N BETWEEN 21W-23W...WHICH MAY BE GETTING MORE SUPPORT FROM THE UPPER DIFFLUENT AIR BETWEEN THE UPPER TROUGH TO THE WNW AND THE UPPER HIGH OVER WRN AFRICA. DEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED DUE TO UNFAVORABLE UPPER-LEVEL WINDS AND COOL OCEAN TEMPERATURES. A WESTERN CARIBBEAN TROPICAL WAVE IS ALONG 82W S OF 20N MOVING W 10 TO 15 KT. THERE IS STILL A WEAK INVERTED V PATTERN SEEN ON SATELLITE IMAGERY BUT THE SIGNAL IS NOT AS CLEAR CUT AS IT HAS BEEN. THE DEEP CONVECTION ASSOCIATED WITH THIS WAVE HAS DIMINISHED IN BOTH COVERAGE AND INTENSITY OVER THE LAST 12HRS...WITH ISOLATED SHOWERS AND TSTMS NOW SEEN FROM 12N-22N BETWEEN 77W-86W. TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 90W/91W S OF 18N MOVING W 10 TO 15 KT. THE ASSOCIATED DEEP CONVECTION IS NOW MOVING INTO THE EPAC WATERS FROM 11N-16N BETWEEN 89W-94W. THERE ALSO APPEARS TO BE SOME SUBTLE CYCLONIC TURNING OF THE LOW TO MID CLOUD FIELD IN THIS REGION. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 8N13W 10N37W 16N43W 16N51W TO INLAND OVER SOUTH AMERICA NEAR 9N61W...EMERGING INTO THE SRN CARIBBEAN AND TO THE COAST OF PANAMA NEAR 9N78W. THE CLUSTER OF SCATTERED MODERATE CONVECTION THAT MOVED OFF THE COAST OF SIERRA LEONE LAST NIGHT IS NOW FROM 6N-9N BETWEEN 14W-17W. ISOLATED SHOWERS/TSTMS ARE WITHIN 100NM OF EITHER SIDE OF THE AXIS BETWEEN 25W-42W. PATCHES OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ALSO SEEN OVER NW COLOMBIA AND THE SW CARIBBEAN FROM 7N-12N BETWEEN 74W-80W. ...DISCUSSION... GULF OF MEXICO... LITTLE SIGNIFICANT WEATHER IS AFFECTING THE GULF THIS MORNING...WITH ABUNDANT DRY MID TO UPPER LEVEL AIR HOVERING OVER THE AREA. THERE ARE A FEW ISOLATED SHOWERS IN THE MIDDLE GULF WATERS FROM 22N-26N BETWEEN 87W-94W...ASSOCIATED WITH UPPER DIFFLUENT AIR BETWEEN THE FLOW AROUND AN UPPER ANTICYCLONE OVER MEXICO AND THE TROUGHING OFF THE U.S. EAST COAST. THESE SMALL CELLS ARE BARELY ABLE TO SUSTAIN THEMSELVES IN THE MIDST OF THE DRY AIR PRESENT. FAIRLY LIGHT 5-15 KT ANTICYCLONIC SE/S FLOW DOMINATES AT THE SURFACE TONIGHT. THE EXCEPTION IS 15-20KT SE/S FLOW IN THE W/NW PORTION WHERE A SLIGHTLY STRONGER GRADIENT IS IN TACT AS THE WRN PORTION OF HIGH PRESSURE INTERACTS WITH LOWER PRESSURE OVER MEXICO...AND A FRONTAL SYSTEM PUSHING INTO NW TEXAS. CARIBBEAN SEA... A TROPICAL WAVE IS TRAVERSING THE WRN CARIBBEAN SEA PRODUCING CONVECTION W OF 78W AS DESCRIBED ABOVE. MUCH OF THE CARIBBEAN E OF 78W IS DOMINATED BY DRY MID TO UPPER LEVEL AIR AND FAIR WEATHER. THE UW-CIMMS SAHARAN AIR LAYER ANALYSIS ALSO SUGGESTS THIS AREA IS UNDER THE INFLUENCE OF DENSE SAHARAN DUST. A MID TO UPPER LEVEL HIGH IS OVER THE NW CARIBBEAN...WITH AN ESTIMATED CENTER NEAR 17N83W. THERE IS A MID TO UPPER LEVEL TROUGH AXIS THAT EXTENDS NORTH FROM VENEZUELA AND INTO THE CARIBBEAN MORE OR LESS ALONG 68W TO NEAR THE MONA PASSAGE...BUT DRY AIR IS INHIBITING CONVECTION. AT THE SURFACE...10-20KT TRADES DOMINATE EXCEPT SLIGHTLY STRONGER N OF THE COLOMBIAN COAST. ATLANTIC OCEAN... PRONOUNCED DEEP LAYER TROUGHING OFF THE US EAST COAST IS ANCHORED BY AN UPPER LOW ABOUT 150NM E OF RODANTHE NORTH CAROLINA. ASSOCIATED SLOW MOVING...NOW DYING COLD FRONT IS OVER THE W ATLC ALONG 32N68W 25N80W. THE MOST SIGNIFICANT CONVECTION ASSOCIATED WITH THIS OLD FRONTAL BOUNDARY IS NOW MOVING THROUGH THE SRN BAHAMAS FROM 23N-25N BETWEEN 76W-78W...ELSEWHERE ISOLATED SHOWERS/TSTMS ARE WITHIN 75NM OF THE FRONTAL BOUNDARY. A MID TO UPPER LEVEL HIGH IS NNE OF THE LEEWARD ISLANDS NEAR 21N62W. OUTFLOW IS SEEN IN SATELLITE IMAGERY OVER THE CENTRAL ATLC HURRICANES GORDON AND HELENE...WITH GOES HIGH DENSITY WINDS ALSO DEPICTING THIS WELL. A MID TO UPPER LEVEL TROUGH IS OVER THE ERN ATLC NEAR 22N32W. UPPER DIFFLUENT AIR BETWEEN THIS FEATURE AND THE UPPER HIGH OVER WRN AFRICA IS HELPING TO SUPPORT THE SCATTERED SHOWERS/TSTMS FROM 19N-30N BETWEEN 16W-23W. ELSEWHERE AT THE SURFACE...A 1016MB HIGH IS CENTERED NEAR 24N65W...WITH A 1023MB HIGH N OF THE AREA NEAR 34N38W...AND A 1022MB HIGH CENTER FURTHER E NEAR 34N17W. $$ WILLIS