000 AXNT20 KNHC 180600 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...SPECIAL FEATURES... THE CENTER OF HURRICANE HELENE WAS NEAR 21.6N 49.4W...OR ABOUT 800 NM EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS AT 18/0300 UTC. HELENE IS MOVING TOWARD THE NORTHWEST AT 7 KT. THIS MOTION IS EXPECTED TO CONTINUE OVERNIGHT WITH A GRADUAL TURN TOWARD THE WEST-NORTHWEST ON MONDAY. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 962 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 100 KT WITH GUSTS TO 120 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 20N-25W FROM 44W-52W...WITH A SYMMETRIC EYE IN THE VICINITY OF 21N-22N BETWEEN 48W-50W. THE CENTER OF HURRICANE GORDON WAS NEAR 35.4N 51.5W OR ABOUT 1185 NM WEST OF THE AZORES AT 18/0300 UTC. GORDON IS MOVING TOWARD THE NORTHEAST AT 12 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 34N-38N BETWEEN 49W-53W. ...TROPICAL WAVES... SATELLITE IMAGERY SUGGESTS THE EASTERN ATLANTIC LOW JUST N OF THE CAPE VERDE ISLANDS HAS TRANSITIONED BACK INTO AN OPEN WAVE. THE WAVE IS PLACED ALONG 24W/25W S OF 20N...MOVING W NEAR 10 KT. SHORTWAVE IR IMAGERY STILL SHOWS CYCLONIC TURNING OF THE LOW TO MID CLOUD FIELD ABOUT THE WAVE AXIS...THOUGH SHOWER AND TSTM ASSOCIATED WITH THIS WAVE REMAINS MINIMAL. A TROPICAL WAVE IS MOVING THROUGH THE YUCATAN PENINSULA AND CENTRAL AMERICA...AND THE EPAC ALONG 88W/89W S OF 22N MOVING W NEAR 15 KT. PATCHES OF SCATTERED MODERATE CONVECTION SEEN FROM 11N-21N BETWEEN 85W-93W...WITH A LINGERING HINT OF AN INVERTED V PATTERN NOTED IN THIS REGION AS WELL. THE NORTHERN END OF A LOW AMPLITUDE TROPICAL WAVE IS MOVING THROUGH SOUTHERN MEXICO AND THE EPAC ALONG 97W S OF 18N MOVING W 10 TO 15 KT. SCATTERED MODERATE CONVECTION IS OVER THE ISTHMUS OF TEHUANTEPEC AND ADJACENT WATERS FROM 15N-18N BETWEEN 93W-96W. A QUIKSCAT PASS NEAR 0000 UTC SHOWED A SMALL REGION OF CYCLONIC TURNING FROM 10N-14N BETWEEN 94W-100W. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N12W 12N23W 10N28W 11N43W 13N48W 10N60W. CLUSTERS OF SCATTERED MODERATE TO STRONG CONVECTION ARE INLAND OVER AFRICA AND BEGINNING TO MOVE INTO THE ADJACENT ERN ATLC WATERS...JUST NORTH OF THE ITCZ FROM 9N-15N BETWEEN 9W-18W. A SMALLER CLUSTER OF MODERATE CONVECTION IS FROM 7N-11N BETWEEN 20W-23W. ISOLATED SHOWERS AND TSTMS ARE NOTED ELSEWHERE WITHIN 200NM OF THE ITCZ BETWEEN 22W-60W. ...DISCUSSION... THE GULF OF MEXICO... A MID TO UPPER LEVEL ANTICYCLONE IS DOMINATING MUCH OF THE GULF OF MEXICO TONIGHT...WITH A CENTER ESTIMATED BY WV IMAGERY AND GOES HIGH DENSITY WINDS NEAR 29N93W OR JUST S OF THE WRN LOUISIANA COAST. THERE IS A SMALL UPPER LOW SEEN SPINNING IN THE SW GULF NEAR 21N96W. OVERALL ABUNDANT DRY MID TO UPPER LEVEL AIR AND FAIR WEATHER IS OVER THE GULF...THOUGH MOISTURE AHEAD OF THE FRONTAL SYSTEM MOVING THROUGH TEXAS AND THE SRN PLAINS IS STREAMING INTO THE NRN GULF AROUND THE UPPER HIGH. THERE ARE ALSO ISOLATED TO SCATTERED SHOWERS AND TSTMS SEEN IN THE SE GULF...WRN FLORIDA KEYS AND FLORIDA STRAITS. 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 IN THE VICINITY. THE REMAINDER OF THE SURFACE PATTERN IS DOMINATED BY ANTICYCLONIC 5-15KT SE FLOW. SHOWERS AND TSTMS AHEAD OF THE FRONT MOVING THROUGH TEXAS WILL MOVE INTO THE NW/N GULF LATER TODAY AND TOMORROW. THE CARIBBEAN SEA... A PAIR OF MID TO UPPER LEVEL ANTICYCLONES ARE OVER THE NW CARIBBEAN NEAR 19N85W AND 19N78W. THE WRN MOST OF THESE MAY BE HELPING TO SUPPORT THE CLUSTER OF SCATTERED MODERATE CONVECTION OVER THE NW CARIBBEAN FROM 19N-20N BETWEEN 85W-88W. THIS IS ALSO LIKELY BEING ENHANCED BY THE TROPICAL WAVE EXITING THE AREA. THE OTHER DEEP CONVECTION SEEN IN THE CARIBBEAN IS IN THE SW PORTION...WITH PATCHES OF MODERATE CONVECTION SEEN FROM 8N-12N BETWEEN 75W-82W. THIS SEEMS MOST ASSOCIATED WITH THE ITCZ. THERE IS A LITTLE UPPER LEVEL MOISTURE BEING ADVECTION 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 TONIGHT. 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 24N79W TO 30N67W...AND ATTACHES TO A 1006MB SURFACE LOW SPINNING ABOUT 300NM E OF CAPE HATTERAS NEAR 35N69W. ISOLATED SHOWERS AND TSTMS ASSOCIATED WITH THIS BOUNDARY ARE NOW MOSTLY LIMITED TO THE WRN KEYS...SRN BAHAMAS AND ADJACENT WATERS. A MID TO UPPER LEVEL HIGH IS JUST NE OF THE LEEWARD ISLANDS NEAR 18N60W. SATELLITE IMAGERY SHOWS THE OUTFLOW OF HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF MID TO UPPER LEVEL LOW IS LOCATED NEAR 21N32W. 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