000 AXNT20 KNHC 170603 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0530 UTC. ...SPECIAL FEATURES... HURRICANE GORDON WAS CENTERED NEAR 32.0N 53.9W OR ABOUT 560 NM EAST OF BERMUDA AT 17/0300 UTC AND IS MOVING NORTH NEAR 3 KT. THIS GENERAL MOTION 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. SLOW WEAKENING IS FORECAST DURING THE NEXT 24 HOURS...AND GORDON IS EXPECTED TO BECOME A TROPICAL STORM ON SUNDAY. 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-56W. HURRICANE HELENE WAS CENTERED NEAR 19.5N 47.5W OR ABOUT 890 NM EAST OF THE NORTHERN LEEWARD ISLANDS AT 17/0300 MOVING WEST-NORTHWEST AT 9 KT. A MOTION BETWEEN WEST-NORTHWEST AND NORTHWEST IS EXPECTED DURING THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 984 MB. MAXIMUM SUSTAINED WIND SPEED IS 70 KT WITH GUSTS TO 85 KT. SLOW 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-23N BETWEEN 45W-50W. ...TROPICAL WAVES... A BROAD 1012MB LOW NEAR 16N23W...MOVING WNW NEAR 10 KT...IS APPROACHING THE EASTERN CAPE VERDE ISLANDS BUT STILL REMAINS ABSENT OF SIGNIFICANT CONVECTION. THIS LOW MAY BE TRANSITIONING BACK INTO AN OPEN WAVE BUT SHORTWAVE IR IMAGERY STILL SHOWS CYCLONIC ROTATION OF THE LOW CLOUD FIELD ABOUT A FIXED POINT SO HAVE KEPT THE LOW. SHOWER ACTIVITY CONTINUES TO DECREASE...AND NO SIGNIFICANT DEVELOPMENT IS EXPECTED AS THE SYSTEM MOVES OVER COOLER WATERS. A WESTERN CARIBBEAN TROPICAL WAVE IS ALONG 80W S OF 18N MOVING W 10 TO 15 KT. SLIGHT VEERING OF THE WINDS AT BUOY 42057 SUGGEST THE WAVE AXIS HAS RECENTLY PASSED...AND THUS HAVE PLACED THE AXIS JUST IN LEE OF THIS BUOY ON THE 2100 UTC MAP. CLUSTERS OF SCATTERED MODERATE CONVECTION ASSOCIATED WITH THIS WAVE ARE SEEN APPROACHING NICARAGUA/HONDURAS FROM 12N-16N BETWEEN 80W-84W...AND ALSO IN THE NW CARIB FROM 17N-20N BETWEEN 78W-86W. TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 88W/89W S OF 17N MOVING W NEAR 10 KT. CYCLONIC TURNING OF THE LOW TO MID CLOUD FIELD IS BEST SEEN IN THE EPAC WATERS OFF CENTRAL AMERICA...THOUGH THE AVAILABLE SFC OBSERVATIONS OVER CENTRAL AMERICA AND SE MEXICO ALSO SUGGEST CYCLONIC TURNING ABOUT THE WAVE AXIS. PATCHES OF SCATTERED MODERATE CONVECTION ARE FROM 11N-17N BETWEEN 87W-93W. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 8N13W 9N37W 16N43W 15N49W TO INLAND OVER SOUTH AMERICA NEAR 9N61W...REEMERGING INTO THE SRN CARIBBEAN AND TO THE COAST OF PANAMA NEAR 9N78W. A SMALL CLUSTER OF SCATTERED MODERATE CONVECTION RECENTLY MOVED OFF THE COAST OF SIERRA LEONE FROM 6N-8N BETWEEN 13W-16W. ISOLATED SHOWERS/TSTMS ARE WITHIN 100NM OF EITHER SIDE OF THE AXIS BETWEEN 24W-43W. ...DISCUSSION... GULF OF MEXICO... LITTLE SIGNIFICANT WEATHER IS AFFECTING THE GULF TONIGHT...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-28N BETWEEN 86W-93W...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. CARIBBEAN SEA... TWO TROPICAL WAVES ARE TRAVERSING THE 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 WRN CARIBBEAN...WITH AN ESTIMATED CENTER NEAR 17N79W. 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 JUST 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 KITTY HAWK NC. ASSOCIATED SLOW MOVING COLD FRONT IS OVER THE W ATLC ALONG 32N69W 25N80W. DOPPLER RADAR AND IR SATELLITE IMAGERY SUGGESTS THE MOST SIGNIFICANT CONVECTION ASSOCIATED WITH THIS FRONT NOW OVER THE FLORIDA STRAITS...ELSEWHERE ISOLATED SHOWERS/TSTMS ARE WITHIN 75NM OF THE FRONTAL BOUNDARY. A MID TO UPPER LEVEL HIGH IS NNE OF THE LEEWARD ISLANDS NEAR 23N62W. 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 ALONG 20N33W 32N26W. UPPER DIFFLUENT AIR BETWEEN THIS FEATURE AND THE UPPER HIGH OVER WRN AFRICA IS HELPING TO SUPPORT THE SCATTERED SHOWERS/TSTMS FROM 18N-29N BETWEEN 16W-24W. ELSEWHERE AT THE SURFACE...A 1018MB HIGH IS CENTERED NEAR 25N63W...WITH A 1024MB HIGH N OF THE AREA NEAR 34N37W...A 1023MB HIGH CENTER FURTHER E NEAR 35N18W. $$ WILLIS