000 AXNT20 KNHC 171810 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURES... THE CENTER OF HURRICANE GORDON AT 17/1500 WAS NEAR 33.6N 53.2W OR ABOUT 1300 NM/2405 KM WEST OF THE AZORES. GORDON IS MOVING NORTH 9 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 983 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 70 KT WITH GUSTS TO 85 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 STRONG SHOWERS AND THUNDERSTORMS ARE WITHIN 60 TO 90 NM OF THE CENTER IN THE SOUTHEASTERN QUADRANT. OTHER SCATTERED MODERATE TO STRONG SHOWERS ARE WITHIN 120 TO 180 NM OF THE CENTER EVERYWHERE ELSE. THE CENTER OF HURRICANE HELENE AT 17/1500 UTC WAS NEAR 20.5N 49.0W...OR ABOUT 810 NM/1500 KM EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS. HELENE IS MOVING NORTHWEST 9 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 970 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 90 KT WITH GUSTS TO 110 KT. PLEASE READ THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC ADVISORY UNDER MIATCPAT2/ WTNT32 KNHC FOR MORE DETAILS. NUMEROUS STRONG SHOWERS AND THUNDERSTORMS ARE WITHIN 60 TO 120 NM OF THE CENTER IN THE NORTHWESTERN QUADRANT. OTHER SCATTERED MODERATE TO STRONG SHOWERS AND THUNDERSTORMS ARE WITHIN 180 TO 260 NM OF THE CENTER EVERYWHERE ELSE. ...TROPICAL WAVES... AN ATLANTIC OCEAN 1012 MB LOW PRESSURE CENTER IS NEAR 18N22W... ABOUT 90 NM TO THE NORTHEAST OF THE NORTHEASTERN CAPE VERDE ISLANDS. THIS LOW CENTER HAS MOVED NORTHWARD 10 KT DURING THE LAST SIX HOURS. NUMEROUS STRONG SHOWERS AND THUNDERSTORMS ARE FROM 20.5N TO 21.5N BETWEEN 20.5W AND 22W. THE AREAL COVERAGE OF STRONG PRECIPITATION WAS COMPARATIVELY BIGGER SIX HOURS AGO. CLOUD TOP TEMPERATURES IN THIS AREA ALSO WERE COMPARATIVELY COLDER...FROM -74C TO -86C. THE COLDEST CLOUD TOP TEMPERATURES IN THIS AREA NOW RANGE FROM -60C TO -70C. IT IS POSSIBLE THAT THIS PRECIPITATION MAY BE GETTING MORE SUPPORT FROM THE UPPER LEVEL DIFFLUENT FLOW BETWEEN THE UPPER TROUGH TO THE WEST- NORTHWEST AND THE UPPER LEVEL HIGH PRESSURE CENTER OVER WESTERN AFRICA. DEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED DUE TO UNFAVORABLE UPPER-LEVEL WINDS AND COOL OCEAN TEMPERATURES. A WESTERN CARIBBEAN SEA TROPICAL WAVE IS ALONG 84W/85W SOUTH OF 20N MOVING WEST 10 TO 15 KT. ISOLATED MODERATE SHOWERS FROM NORTHERN NICARAGUA TO EASTERN HONDURAS. THE NORTHERN END OF A TROPICAL WAVE IS MOVING THROUGH SOUTHERN MEXICO...NOW OVER THE AREA JUST EAST OF THE ISTHMUS OF TEHUANTEPEC. THE ONLY NEARBY PRECIPITATION IS STRONG THUNDERSTORMS WITHIN A 30 NM RADIUS OF 15.5N 95W AT THE EDGE OF THE SOUTHERN GULF OF TEHUANTEPEC IN THE EASTERN PACIFIC OCEAN. ...THE ITCZ... ITCZ 6N11W 8N18W 9N24W 9N39W 15N42W 15N45W 10N51W 10N60W. SCATTERED TO NUMEROUS STRONG SHOWERS AND THUNDERSTORMS ARE FROM 6N TO 9N BETWEEN 16W AND 19W. ISOLATED MODERATE SHOWERS FROM 7N TO 13N BETWEEN 31W AND 41W...AND WITHIN 30 TO 45 NM ON EITHER SIDE OF 16N44W 13N47W 9N52W. ...DISCUSSION... THE GULF OF MEXICO... MIDDLE TO UPPER LEVEL DRY AIR IS NORTH AND NORTHWEST OF THE LINE FROM 24N80W TO THE NORTHERN YUCATAN PENINSULA TO THE SOUTHWESTERN GULF OF MEXICO. UPPER LEVEL ANTICYCLONIC FLOW COVERS THE GULF WATERS. A HIGH LEVEL RIDGE RUNS FROM CENTRAL INTERIOR MEXICO TO CENTRAL TEXAS AND BEYOND SOUTHWESTERN ARKANSAS. UPPER LEVEL ANTICYCLONIC FLOW IS RIDING OVER THE TOP OF THE ANTICYCLONIC FLOW ASSOCIATED WITH THE TAIL END OF THE ATLANTIC OCEAN-TO-FLORIDA STRAITS DEEP LAYER TROUGH. ISOLATED MODERATE SHOWERS AND POSSIBLE THUNDERSTORMS ARE WITHIN A 30 NM RADIUS OF 27N84W...FROM 28.5N TO 29.5N BETWEEN 86W AND 88W... AND OVER SECTIONS OF SOUTHEASTERN LOUISIANA. AN EARLIER MASS OF NUMEROUS STRONG SHOWERS AND THUNDERSTORMS OVER SOUTH TEXAS HAS WEAKENED IN INTENSITY AND COLD CLOUD TOP TEMPERATURES. PRECIPITATION MAY BE LINGERING IN SOUTH TEXAS STILL. THE CARIBBEAN SEA... NUMEROUS STRONG SHOWERS AND THUNDERSTORMS ARE IN THE SOUTHWESTERN CORNER OF THE AREA...SOUTHWEST OF 11N77W 12N80W. THIS PRECIPITATION IS TAKING PLACE UNDER AN UPPER LEVEL RIDGE WHICH RUNS FROM THE SOUTHEAST TO THE NORTHWEST...ANCHORED AROUND A 14N84W UPPER LEVEL HIGH PRESSURE CENTER IN NORTHEASTERN NICARAGUA. AN APPROACHING MIDDLE TO UPPER LEVEL INVERTED TROUGH CURRENTLY IS ALONG 15N67W TO 12N71W TO 9N73W. MIDDLE TO UPPER LEVEL DRY AIR ON WATER VAPOR SATELLITE IMAGERY COVERS THE REST OF THE CARIBBEAN SEA EAST OF 77W. THE ATLANTIC OCEAN... CYCLONIC FLOW COVERS THE WESTERN ATLANTIC OCEAN WEST OF 32N67W 26N73W 25N80W. A PRONOUNCED DEEP LAYER TROUGH PASSES THROUGH 35N71W 32N73W TO THE NORTHERN BAHAMAS TO 25N80W IN THE STRAITS OF FLORIDA JUST SOUTH OF THE FLORIDA COAST. MIDDLE TO UPPER LEVEL DRY AIR IS WEST OF THE 32N67W 25N80W LINE. A DISSIPATING SURFACE COLD FRONT PASSES THROUGH 32N68W TO 30N68W TO 28N70W... CUTTING ACROSS THE NORTHERN BAHAMAS TO THE STRAITS OF FLORIDA NEAR 24N80W. WIDELY SCATTERED MODERATE SHOWERS TO ISOLATED STRONG THUNDERSTORMS WITHIN 75 TO 150 NM ON EITHER SIDE OF 34N61W 29N66W 26N67W 25N71W 24N80W. SURFACE HIGH PRESSURE IS BUILDING OVER FLORIDA AND THE ATLANTIC OCEAN TO THE WEST AND NORTHWEST OF THE FRONT. A MIDDLE TO UPPER LEVEL HIGH PRESSURE CENTER IS NORTH-NORTHEAST 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 MIDDLE TO UPPER LEVEL TROUGH RUNS FROM TO A LOW PRESSURE CENTER NEAR 21N32W TO 15N36W. UPPER LEVEL DIFFLUENT FLOW BETWEEN THIS FEATURE AND THE UPPER HIGH OVER WESTERN AFRICA IS HELPING TO SUPPORT THE SCATTERED SHOWERS AND THUNDERSTORMS TO THE NORTHEAST OF THE 18N22W SURFACE LOW PRESSURE CENTER. AN EASTERN ATLANTIC OCEAN 1024 MB HIGH PRESSURE CENTER IS NEAR 35N16W. A 1024 MB HIGH PRESSURE CENTER IS NEAR 34N38W. A DISSIPATING COLD FRONT IS IN BETWEEN THESE TWO HIGH PRESSURE CENTERS. BROAD SURFACE HIGH PRESSURE IS EAST OF HURRICANE GORDON AND TO THE NORTHEAST OF HURRICANE HELENE. $$ MT