000 AXNT20 KNHC 111053 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...SPECIAL FEATURE... TROPICAL DEPRESSION GABRIELLE IS ACCELERATING TOWARD THE NORTH ATLANTIC. AS OF 11/0900 UTC THE CENTER OF THE DEPRESSION WAS NEAR 39.0N 66.8W OR ABOUT 205 NM SOUTHEAST OF NANTUCKET MASSACHUSETTS. GABRIELLE IS MOVING EAST-NORTHEAST AT 18 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 HAS GAINED SOME CONVECTION OVERNIGHT. HOWEVER...ALL OF THIS CONVECTION IS LOCATED TO THE E OF THE EXPOSED LOW LEVEL CENTER AS THIS SYSTEM IS EMBEDDED WITHIN A HIGHLY SHEARED ENVIRONMENT. THESE CONVECTIVE BURSTS WILL LIKELY NOT LAST MORE THAN ANOTHER DAY OR SO AS A STRONG UPPER SHORTWAVE...CURRENTLY OVER THE GREAT LAKES...APPROACHES AND ABSORBS THIS SYSTEM. A BROAD AREA OF LOW PRESSURE IN THE CENTRAL ATLC...ANALYZED 1010 MB NEAR 11N43W...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 CHANGED LITTLE OVERNIGHT BUT STILL 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 WAS ADJUSTED A FEW DEGREES TO THE WEST PASSED THE CAPE VERDE ISLANDS ALONG 27W/28W S OF 22N MOVING W 15 KT. THIS ADJUSTMENT WAS BASED PRIMARILY ON THE DISTINCT LOW LEVEL TURNING SEEN ON THE FIRST FEW VIS IMAGES OF THE DAY AND THE CIMSS TPW ANIMATION. THESE DATA SOURCES SHOW ROTATION MOST CONCENTRATED ACROSS THE NRN EXTENSION AND IT APPEARS AS IF A WEAK LOW IS TRYING TO FORM ALONG THE AXIS NEAR 17N...ALTHOUGH IT MAY NOT BE AT THE SFC. WHILE THE WAVE STRUCTURE IS WELL DEFINED...CONVECTION REMAINS CONFINED WELL TO THE SW OF THE AXIS WITHIN THE INTERSECTION OF THE ITCZ FROM 9N-13N BETWEEN 29W-35W. TROPICAL WAVE IS IN THE E CARIB ALONG 65W S OF 20N MOVING W 10 TO 15 KT. THIS WAVE HAS BECOME ILL-DEFINED WITH SATELLITE IMAGES REVEALING LITTLE SIGNATURE. THE CURRENT POSITION IS BASED ON THE CIMSS TPW ANIMATION WHICH SHOWS A WWD NARROWING SURGE OF MOISTURE ASSOCIATED WITH THIS WAVE. THE LARGE CLUSTER OF CONVECTION THAT WAS ALONG THE N PART OF THE AXIS EARLIER HAS WEAKENED AND STRETCHED LINEARLY IN A HIGHLY DIFFLUENT UPPER PATTERN. MORE ON THIS AREA OF WEATHER IN THE ATLANTIC DISCUSSION BELOW. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 12N17W 13N29W 12N41W 8N52W 8N60W. BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES AND BROAD LOW...ISOLATED MODERATE IS WITHIN 90 NM OF THE AXIS W OF 45W AND WITHIN 120 NM S OF THE AXIS E OF 17W POSSIBLY ASSOCIATED WITH THE NEXT TROPICAL WAVE. DISCUSSION... THE GULF OF MEXICO... THE MAIN FEATURE IN THE GULF IS A 1010 MB LOW PRES SYSTEM CENTERED NEAR 26N95W. THIS LOW SITS ALONG A N-S TROUGH AXIS WHICH RUNS ALONG 95W N OF 22N. THIS LOW AND TROUGH SHOW UP NICELY IN THE SHIP...BUOY AND EARLIER QSCAT DATA. WHILE THERE IS ABUNDANT UPPER MOISTURE IN PLACE ACROSS MOST OF THE GULF...THERE ARE ONLY SCATTERED DEEPENED PATCHES. LATEST IR IMAGES SHOW SCATTERED SHOWERS AND TSTMS WITHIN 180 NM OF THE LOW. A CLUSTER OF SCATTERED MODERATE TO STRONG CONVECTION HAS RECENTLY DEVELOPED IN THE BAY OF CAMPECHE S OF 20N BETWEEN 92W-95W FUELED PRIMARILY BY DIFFLUENCE ALOFT. SIMILAR ACTIVITY IS OVER THE E GULF AND W FLORIDA TO THE SE OF AN UPPER LOW CENTERED NEAR 27N85W. 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 UPPER-LEVEL WINDS COULD BECOME A LITTLE MORE FAVORABLE FOR DEVELOPMENT OF THIS SYSTEM PRIOR TO IT REACHING THE COAST OF TEXAS AND NORTHEASTERN MEXICO TONIGHT OR EARLY WEDNESDAY. THE CARIBBEAN SEA... A LARGE UPPER LEVEL LOW HAS BEEN DRIFTING SLOWLY W CURRENTLY SPINNING S OF HISPANIOLA NEAR 16N73W. DIFFLUENCE BETWEEN THIS UPPER SYSTEM AND AN UPPER HIGH TO THE E...ALONG WITH SOME LOW-LEVEL INFLUENCE ASSOCIATED WITH A TROPICAL WAVE...IS SUPPORTING AN AREA OF CLOUDINESS AND ISOLATED SHOWERS E OF 65W ESPECIALLY OVER THE SRN WINDWARDS. BETTER ORGANIZED MOISTURE IS FURTHER N WHERE DIFFLUENCE IS MORE PRONOUNCED. INSTABILITY AND DIFFLUENCE PARTIALLY ASSOCIATED WITH THE UPPER LOW IS ALSO HELPING TO SUSTAIN CLUSTERS OF SCATTERED MODERATE CONVECTION IN THE W CARIB. ONE OF THE MORE NOTABLE CLUSTERS IS IN THE SW PORTION FROM 11N-15N BETWEEN 79W-83W. A WEAKER MORE DISORGANIZED BATCH IS N OF 21N EXTENDING INTO THE SE GULF FROM 81W-86W. 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 32N62W AND A 1021 MB CENTER NEAR 34N27W. THIS RIDGE IS INTERRUPTED IN THE CENTRAL ATLC DUE TO A TRAILING SFC TROUGH WHICH ENTERS THE REGION NEAR 32N42W AND EXTENDS SW TO 27N50W. 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 IN OUR AREA IS THE WEAKENED GRADIENT IT HAS PRODUCED. THIS HAS ALLOWED LIGHT WINDS TO PREVAIL 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 67W. 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 35W-67W. DIFFLUENCE BETWEEN ALL OF THESE UPPER SYSTEMS HAS GENERATED A LINEARLY STRETCHED AREA OF SHOWERS AND TSTMS FROM 23N-25N BETWEEN 59W-72W. UPPER RIDGING DOMINATES THE PATTERN FARTHER E THE RIDGE AXIS ALIGNED NE-SW 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