000 AXNT20 KNHC 101751 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON SEP 10 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN 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...METEOROLOGICAL ANALYSIS... WEATHER OBSERVATIONS...AND RADAR. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURE... TROPICAL DEPRESSION GABRIELLE CONTINUES TO MOVE AWAY FROM THE UNITED STATES. AS OF 10/1500 UTC THE CENTER OF THE DEPRESSION WAS NEAR 37.1N 73.0W OR ABOUT 285 NM SOUTH-SOUTHWEST OF NANTUCKET MASSACHUSETTS. GABRIELLE IS MOVING EAST-NORTHEAST AT 11 KT. MAXIMUM SUSTAINED WINDS REMAIN 30 KT WITH GUSTS TO 40 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1009 MB. PLEASE REFER TO THE NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND/OR THE PUBLIC ADVISORY MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. DURING THE PAST SEVERAL HOURS A SMALL AREA OF THUNDERSTORMS HAS DEVELOPED ABOUT 75 NM SOUTHEAST OF THE CENTER. HOWEVER...NORTHWESTERLY SHEAR HAS NOT ALLOWED THIS THUNDERSTORM ACTIVITY TO ACQUIRE MUCH CURVATURE. THE NHC OFFICIAL FORECAST WILL MAINTAIN THE CYCLONE AS A 30 KT DEPRESSION UNTIL IT MERGES WITH A LARGER EXTRATROPICAL LOW IN ABOUT 48 HOURS. GABRIELLE IS EXPECTED TO PASS WELL SOUTH OF THE COAST OF THE NORTHEASTERN UNITED STATES. ...TROPICAL WAVES... TROPICAL WAVE IS JUST EAST OF THE CAPE VERDE ISLANDS ALONG 22W S OF 19N MOVING W 10-15 KT. ALTHOUGH A BROAD CYCLONIC TURNING IS SEEN OF SFC DATA...THE WAVE LOOKS FAIRLY DISORGANIZED ON SATELLITE IMAGERY. AN EARLIER QUIKSCAT PASS DID NOT SHOW A SFC CLOSED CIRCULATION AND THE ASCAT MISSED THE SYSTEM. SCATTERED MODERATE CONVECTION IS CONFINED TO AN AREA W OF THE AXIS FROM 10N-17N BETWEEN 22W-26W. AN ACTIVE TROPICAL WAVE IS ALONG 40W/41W S OF 16N. THIS SYSTEM WAS SLIGHTLY ADJUSTED AHEAD BASED ON SATELLITE IMAGERY AND THE POSITION OF THE SFC LOW ALONG THE WAVE AXIS...WHICH IS NEAR 9N41W WITH 1010 MB. IT IS PRODUCING A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS. THIS SYSTEM IS GRADUALLY BECOMING BETTER ORGANIZED AND HAS THE POTENTIAL TO DEVELOP INTO A TROPICAL DEPRESSION DURING THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD AT 10-15 MPH. TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 61W S OF 20N. A BURST OF CONVECTION HAS DEVELOPED ON THE NORTHERN SIDE OF THE WAVE FROM 14N-18N BETWEEN 60W-63W. THIS WAVE SHOWS UP FAIRLY WELL IN THE SHIP/BUOY DATA AND SATELLITE PHOTOS. THE WAVE IS GENERATING MAINLY LIGHT SHOWERS AND TSTMS OVER THE ISLANDS... PARTICULARLY BETWEEN MARTINIQUE AND ANTIGUA. SIGNIFICANT DEVELOPMENT OF THIS SYSTEM IS NOT EXPECTED AS IT MOVES WEST-NORTHWESTWARD AT ABOUT 15 MPH. MOISTURE FROM THIS WAVE WILL AFFECT THE UK/US VIRGIN ISLANDS AND PUERTO RICO THIS EVENING AND TONIGHT. THE NRN PORTION OF A TROPICAL WAVE ALONG 94W EXTENDS INTO THE BAY OF CAMPECHE S OF 20N MOVING W 10-15 KT. THERE IS A FAIR AMOUNT OF MOISTURE IN THIS AREA. HOWEVER...IT IS DIFFICULT TO TELL HOW MUCH OF THIS IS RELATED TO THE WAVE ITSELF AS THERE IS A WELL DEFINED UPPER TROUGH AND LOW-LEVEL TROUGHING IN THIS GENERAL AREA AS WELL. MORE ON THIS IN THE GULF OF MEXICO SECTION BELOW. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 8N13W 9N21W 10N35W 8N45W 10N60W. BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES... CLUSTERS OF SCATTERED MODERATE/ ISOLATED STRONG CONVECTION ARE WITHIN 100 NM N OF AXIS WEST OF 50W. DISCUSSION... THE GULF OF MEXICO... A LARGE BUT DISORGANIZED AREA OF CLOUDINESS AND THUNDERSTORMS IS OVER THE CENTRAL AND SOUTHWESTERN GULF OF MEXICO. SEVERAL FEATURES ARE ENHANCING THIS CONVECTIVE ACTIVITY. THEY ARE...A SFC TROUGH THAT RUNS FROM THE MOUTH OF THE MISSISSIPPI TO A 1011MB LOW LOCATED NEAR 23N93W...THE NORTHERN EXTENSION OF A TROPICAL WAVE ALONG 94W/95W...AND AN UPPER LOW LOCATED ALONG THE MEXICAN COAST BETWEEN TAMPICO AND VERACRUZ. CONDITIONS DO NOT APPEAR FAVORABLE FOR SIGNIFICANT DEVELOPMENT OF THIS SYSTEM AS IT MOVES SLOWLY WESTWARD OR WEST-NORTHWESTWARD DURING THE NEXT DAY OR TWO. SAT IMAGES AND LIGHTNING DATA REVEAL POCKETS OF SCATTERED SHOWERS AND TSTMS...IN THIS MOIST AND UNSTABLE ENVIRONMENT. AN UPPER RIDGE DOMINATES THE N GULF WATERS SUPPORTING FAIR WEATHER. THE GFS MODEL MOVES ALL THIS MOISTURE NWD MERGING WITH A NEW TROUGH OR WEAK FRONT THAT IS EXPECTED TO PUSH OFF THE TEXAS COAST WED. THIS WILL ALLOW THE SFC PATTERN TO REMAIN WEAK KEEPING WINDS MOSTLY LIGHT. THE CARIBBEAN SEA... A TROPICAL WAVE IS JUST ENTERING THE BASIN PRODUCING SCATTERED SHOWERS AND TSTMS OVER THE LESSER ANTILLES. SEE THE TROPICAL WAVE SECTION ABOVE. SCATTERED MODERATE CONVECTION IS ALONG THE ATLANTIC COAST OF NICARAGUA AND THE SW CARIBBEAN. A DIFFLUENT PATTERN ALOFT BETWEEN A WEAK UPPER HIGH OVER CENTRAL AMERICA AND AN UPPER LOW COVERING THE E CARIBBEAN IS HELPING TO DEVELOP THIS CONVECTIVE ACTIVITY. ELSEWHERE...TYPICAL TRADE WIND SHOWERS ARE SEEN. MODERATE TRADE WINDS ARE BLOWING ACROSS THE REGION WITH 20 KT WINDS CONFINED TO NEAR THE COLOMBIAN COAST. THESE WINDS ARE ANTICIPATED TO INCREASE E OF 75W OVER THE NEXT COUPLE OF DAYS AS THE GRADIENT TIGHTENS BETWEEN RIDGE N OF AREA AND THE COLOMBIAN LOW. THE ATLANTIC OCEAN... A LARGE NEARLY STATIONARY VERTICALLY STACKED LOW PRES SYSTEM IS LOCATED WELL N OF THE AREA IN THE CENTRAL ATLC. TWO WEAK ASSOCIATED SFC TROUGHS STRETCH THROUGH THE AREA. THE MAIN OLD FRONTAL BOUNDARY ENTERS THE AREA NEAR 32N37W AND EXTENDS MAINLY SW ALONG 25N50W 24N65W...THEN CONTINUES NW AND N TO 28N68W. THE TROUGH IS PRETTY ACTIVE WEST OF 55W...WHERE SAT PICTURES SHOWS A 50-60 NM WIDE BAND OF SHOWERS AND TSTMS. A POST-FRONTAL BOUNDARY WITH MUCH LESS SHOWER ACTIVITY IS CLIPPING THE AREA ALONG 30N BETWEEN 46W AND 57W. THIS WEATHER PATTERN KEEPS THE SFC WINDS VERY LIGHT ACROSS THE BULK OF THE CENTRAL ATLC. MODERATE TRADE WINDS ARE FOUND SOUTH OF 20N. A 1022 MB HIGH IS NEAR 32N64W WITH A RIDGE EXTENDING OVER THE W ATLC AND THE STATE OF FLORIDA. ALOFT...A RIDGE/TROUGH/RIDGE DOMINATES THE FORECAST AREA. A RIDGE...ANCHORED ON A HIGH OVER THE SE U.S. COVERS MOST OF THE W ATLC. AN INVERTED TROUGHING IS ALONG 65W/66W S OF 23N. FARTHER EAST...THERE IS A DEEP LAYERED TROUGH THAT SUPPORTS THE AFOREMENTIONED SFC TROUGHS. AN UPPER HIGH LOCATED N OF THE CAPE VERDE ISLANDS NEAR 22N25W IS IN CONTROL OF THE REMAINDER OF THE AREA PROVIDING FAIR WEATHER. OF NOTE...TODAY MARKS THE CLIMATOLOGICAL PEAK OF THE HURRICANE SEASON. SO FAR...THE ONLY HURRICANES THAT HAVE FORMED...DEAN AND FELIX...BECAME CATEGORY FIVE HURRICANES ON THE SAFFIR-SIMPSON SCALE. IN ADDITION BOTH DEAN AND FELIX MADE LANDFALL AS CATEGORY FIVE HURRICANES WITH SUSTAINED WINDS OF NEAR 145 KT AND 140 KT RESPECTIVELY. THIS REPRESENTS THE FIRST TIME THAT TWO CATEGORY FIVE HURRICANES HAVE MADE LANDFALL IN THE ONE SEASON. $$ GR