000 AXNT20 KNHC 110550 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 AM EDT TUE SEP 11 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...SPECIAL FEATURE... TROPICAL DEPRESSION GABRIELLE IS ACCELERATING AWAY FROM THE UNITED STATES. AS OF 11/0300 UTC THE CENTER OF THE DEPRESSION WAS NEAR 38.1N 68.8W OR ABOUT 200 NM SOUTH-SOUTHEAST OF NANTUCKET MASSACHUSETTS. GABRIELLE IS MOVING EAST-NORTHEAST AT 17 KT. MAXIMUM SUSTAINED WINDS REMAIN NEAR 30 KT WITH GUSTS TO 40 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 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. GABRIELLE CONTINUES TO HANG ON AS A TROPICAL CYCLONE BUT IT IS NOT EXPECTED TO LAST MORE THAN A COUPLE MORE DAYS AS A STRONG UPPER SHORTWAVE ...CURRENTLY OVER THE GREAT LAKES...APPROACHES. AN AREA OF SCATTERED MODERATE CONVECTION HAS INCREASED AND EXPANDED A BIT WITHIN 90 NM E OF THE CENTER. A BROAD AREA OF LOW PRESSURE IN THE CENTRAL ATLC...ANALYZED 1010 MB NEAR 10N43W...ASSOCIATED WITH A TROPICAL WAVE CONTINUES TO PRODUCE AN AREA OF SCATTERED MODERATE CONVECTION ROUGHLY WITHIN 120 NM OF THE LOW AND FURTHER E NEAR THE INTERSECTION OF THE ITCZ FROM 11N TO 13N BETWEEN 36W AND 41W. THIS SYSTEM HAS BEEN ON A GRADUAL ORGANIZING TREND AND IT COULD DEVELOP INTO A TROPICAL DEPRESSION WITHIN A DAY OR TWO AS IT MOVES WESTWARD TO WEST-NORTHWESTWARD NEAR 10 KT. ...TROPICAL WAVES... TROPICAL WAVE EXTENDS ACROSS THE CAPE VERDE ISLANDS ALONG 24W S OF 18N MOVING W 10 TO 15 KT. THIS WAVE HAS GENERALLY CHANGED LITTLE SINCE MOVING OFF THE AFRICAN COAST ABOUT 36-48 HOURS AGO. A FAIR AMOUNT OF LOW TO MID LEVEL TURNING IS CLEARLY NOTED IN THE LOW LEVEL CLOUD FIELD AS SEEN ON NIGHT CHANNEL VIS IMAGES AND IN THE CLOUD DRIFT WINDS. AN EARLIER QSCAT PASS SHOWS A NEARLY CLOSED CIRCULATION ALONG THE WAVE AXIS NEAR 15N. WHILE THE WAVE STRUCTURE IS WELL DEFINED...CONVECTION REMAINS CONFINED WELL TO THE SW OF THE DISTINCT TURNING WITHIN THE INTERSECTION OF THE ITCZ FROM 9N-13N BETWEEN 28W-33W. TROPICAL WAVE IS IN THE E CARIB ALONG 63W S OF 20N MOVING W 10 TO 15 KT. A NWD MOVING CLUSTER OF SCATTERED MODERATE CONVECTION IS OVER THE N PORTION OF THE WAVE IN AN UPPER DIFFLUENT ZONE FROM 19N-22N BETWEEN 61W-65W. THE REMAINDER OF THE WAVE AXIS IS ILL DEFINED WITH LIMITED CLOUDINESS. SIGNIFICANT DEVELOPMENT IS NOT EXPECTED. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 7N13W 9N23W 11N36W 8N52W 9N62W. BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES AND BROAD LOW...SCATTERED MODERATE IS WITHIN 75 NM OF THE AXIS BETWEEN 47W-51W. DISCUSSION... THE GULF OF MEXICO... THE MAIN FEATURE IN THE GULF IS A 1010 MB LOW PRES SYSTEM CENTERED NEAR 25N94W. THIS LOW SITS ALONG A N-S TROUGH AXIS WHICH RUNS ALONG 94W N OF 22N. THIS LOW AND TROUGH SHOW UP NICELY IN THE SHIP...BUOY AND QSCAT DATA. WHILE THERE IS ABUNDANT UPPER MOISTURE IN PLACE ACROSS MOST OF THE GULF...VERY LITTLE OF THIS IS BEING DEEPENED. LATEST IR IMAGES...BEFORE THE ECLIPSE...SHOW A SMALL AREA OF SHOWERS AND TSTMS WITHIN 60 NM TO THE W OF THE LOW. SIMILAR ACTIVITY IS OVER THE E GULF AND W FLORIDA TRIGGERED BY AN UPPER LOW CENTERED NEAR 27N84W. ISOLATED SHOWERS COULD OCCUR JUST ABOUT ANYWHERE ELSE IN THE GULF WITHIN THE MOIST ENVIRONMENT. THE ONLY EXCEPTION IS ACROSS THE COASTAL WATERS OF THE N CENTRAL AND NW GULF WHERE A NARROW SWATH OF STABLE AIR ALOFT EXISTS IN AN AREA OF CONFLUENCE BETWEEN A HIGHLY STRETCHED UPPER HIGH OVER THE S U.S. AND THE COMPLEX TROUGHING PATTERN OVER THE GULF. THE SFC LOW PRES SYSTEM IS BEING CLOSELY MONITORED AS THERE APPEARS TO BE SOME CHANCE FOR SLOW DEVELOPMENT BEFORE IT MOVES INLAND OVER MEXICO OR S TEXAS IN A DAY OR SO. THE CARIBBEAN SEA... A LARGE UPPER LEVEL LOW HAS BEEN DRIFTING SLOWLY W CURRENTLY SPINNING S OF HISPANIOLA NEAR 16N72W. DIFFLUENCE BETWEEN THIS UPPER SYSTEM AND AN UPPER HIGH TO THE E...ALONG WITH LOW-LEVEL LIFT PRODUCED BY A TROPICAL WAVE...IS SUPPORTING HIGH LEVEL CLOUDINESS AND ISOLATED SHOWERS ACROSS THE LESSER ANTILLES. MUCH DEEPER MOISTURE IS FURTHER NE WHERE DIFFLUENCE IS MORE PRONOUNCED. INSTABILITY ASSOCIATED WITH THE UPPER LOW IS ALSO HELPING TO SUSTAIN WIDELY SCATTERED MODERATE CLUSTERS OF CONVECTION IN THE W CARIB. ONE OF THE MORE NOTABLE CLUSTERS IS S OF CUBA N OF 20N BETWEEN 78W-82W WHERE LOCAL FLOWS ARE FOR SURE PLAYING A PART. ANOTHER BATCH IS FROM 13N-16N W OF 78W...BUT THIS AREA HAS BEEN ON A WEAKENING TREND OVER THE PAST FEW HOURS. MUCH DRIER AIR LIES OVER THE CENTRAL CARIB WITHIN THE CIRCULATION OF THE UPPER LOW. TRADE WINDS HAVE INCREASED A BIT SINCE YESTERDAY WITH AN EARLIER QSCAT PASS SHOWING A SOLID AREA OF 20 KT WINDS BETWEEN COLOMBIA AND HISPANIOLA. THE ATLANTIC OCEAN... MODERATE SUBTROPICAL RIDGING IS THE GENERAL THEME DISPLAYED ON OUR SFC MAP THIS MORNING. A 1023 MB HIGH CENTER IS LOCATED NEAR 32N63W AND A 1022 MB CENTER NEAR 32N28W. THIS RIDGE IS INTERRUPTED IN THE CENTRAL ATLC DUE TO A TRAILING SFC TROUGH WHICH ENTERS THE REGION NEAR 32N40W AND EXTENDS SW TO 28N53W. ISOLATED SHOWERS ARE POSSIBLE WITHIN 30 NM OF THE TROUGH AXIS. THIS WEAK BOUNDARY IS ASSOCIATED WITH A LARGE OCCLUDED LOW PRES SYSTEM LOCATED WELL N OF THE AREA. AS MENTIONED IN PREVIOUS DISCUSSIONS...THE PRIMARY EFFECT OF THIS LOW PRES SYSTEM S OF 32N IS LIGHTENING THE WINDS IN THE SUBTROPICAL CENTRAL ATLC. ELY TRADES ARE MODERATE ELSEWHERE. IN THE MID AND UPPER LEVELS...RIDGING IS THE PATTERN ACROSS THE W ATLC N OF 26N W OF 65W. TROUGHING TAKES OVER S OF 26N ASSOCIATED WITH THE NRN EXTENSION OF A CARIB UPPER LOW. HIGHLY ELONGATED TROUGHING EXTENDS SW FROM THE DEEP LAYERED LOW IN THE N CENTRAL ATLC AND ROUGHLY COVERS THE AREA N OF 25N BETWEEN 36W-65W. DIFFLUENCE BETWEEN ALL OF THESE UPPER SYSTEMS HAS GENERATED AN AREA OF CLOUDINESS AND SHOWERS N OF THE LESSER ANTILLES. DEBRIS CLOUDINESS IS BEING STRETCHED BOTH E AND W OF THE CLUSTER BY THE DIVERGENT UPPER FLOW. UPPER RIDGING IS THE PATTERN FARTHER E SUPPORTED BY AN NE-SW ALIGNED RIDGE WITH SEVERAL EMBEDDED ANTICYCLONES. THE MEAN AXIS RUNS FROM THE W COAST OF AFRICA TOWARD THE E CARIB ALONG 21N17W 17N45W 15N56W. PRIMARILY DRY STABLE AIR COVERS THE REGIONS NOT OUTLINED ABOVE. $$ CANGIALOSI