000 AXNT20 KNHC 081154 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SAT SEP 08 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 1015 UTC. ...SPECIAL FEATURE... SUBTROPICAL STORM GABRIELLE WAS CENTERED NEAR 31.2N 73.8W OR ABOUT 245 NM SOUTH-SOUTHEAST OF CAPE LOOKOUT NORTH CAROLINA AT 08/1200 UTC. GABRIELLE IS MOVING W-NW AT 10 KT...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE DURING THE NEXT 24 HOURS WITH A GRADUAL DECREASE IN FORWARD SPEED. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1011 MB. MAXIMUM SUSTAINED WINDS ARE 40 KT WITH GUSTS TO 50 KT. SLIGHT STRENGTHENING IS EXPECTED AS GABRIELLE ACQUIRES TROPICAL CHARACTERISTICS. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32 KNHC AND THE FULL FORECAST ADVISORY UNDER MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS INCLUDING THE LATEST WATCH AND WARNING INFORMATION. GABRIELLE LOOKS A LITTLE BETTER ON SATELLITE THIS MORNING AND APPEARS TO BE TAKING ON MORE TROPICAL LIKE CHARACTERISTICS...WITH A CURVED BAND NOW OVER THE N AND W QUADRANTS. THIS BAND OF SCATTERED MODERATE CONVECTION IS FROM 31N-34N BETWEEN 70W-75W. ...TROPICAL WAVES... AN EAST ATLANTIC TROPICAL WAVE IS ALONG 26W S OF 20N MOVING WEST NEAR 15 KT. THIS WAVE CONTINUES TO EXHIBIT A BROAD ENVELOPE OF CYCLONIC TURNING. THE FIRST FEW METSAT-9 VISIBLE IMAGES REVEAL A MID LEVEL CIRCULATION ALONG THE WAVE AXIS NEAR 11N. A RECENT QUIKSCAT PASS REVEALED AN ELONGATED TROUGH AXIS STRETCHING ENE ALONG 7N38W 9N26W 13N20W. THIS WAVE IS PRODUCING A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS...WITH THE STRONGEST ACTIVITY NOTED FROM 10N-13N BETWEEN 28W-33W...AND ALSO FROM 12N-15N BETWEEN 22W-26W. THIS SYSTEM HAS THE POTENTIAL FOR SOME DEVELOPMENT DURING THE NEXT FEW DAYS. AN ATLANTIC OCEAN TROPICAL WAVE IS GENERALLY ALONG 51W/52W SOUTH OF 22N MOVING WEST NEAR 15 KT. THIS WAVE WAS ADJUSTED SLIGHTLY TO THE E BASED ON ITS APPEARANCE IN SATELLITE IMAGERY SHOWING A BROAD AREA OF LOW LEVEL CYCLONIC TURNING...AND ALSO AN EARLIER ASCAT PASS. IN ADDITION...WINDS AT BUOY 41040 HAVE REMAINED FROM THE NE OVER THE LAST SEVERAL HOURS SUGGESTING THE WAVE HAS YET TO PASS. SHOWER ACTIVITY HAS INCREASED SLIGHTLY WITH THE WAVE...WITH LIGHTNING DATA NOW DEPICTING SCATTERED TSTMS FROM 15N-17N BETWEEN 51W-56W. OVERALL THOUGH THE CONVECTION IS MINIMAL AND DISORGANIZED. A SEPARATE 1013 MB LOW PRESSURE CENTER IS E OF THE WAVE AXIS NEAR 12N46W...WHICH IS NEARLY STATIONARY AND DISSIPATING. TROPICAL WAVE IS ALONG 85W/86W SOUTH OF 19N THROUGH CENTRAL AMERICA MOVING WEST 15 KT. THIS WAVE REMAINS DIFFICULT TO LOCATE IN SATELLITE IMAGERY AND THE SURROUNDING SFC OBSERVATIONS...THUS THE POSITION IS BASED MOSTLY ON EXTRAPOLATION. THE CONVECTION OVER THE SW CARIBBEAN SEEMS MORE ASSOCIATED WITH THE ITCZ. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 15N17W 7N30W 8N50W 8N60W. A FAIRLY LARGE CLUSTER OF MODERATE TO STRONG CONVECTION IS MOVING OFF THE AFRICAN COAST FROM 14N-19N BETWEEN 15W-20W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 27W-38W. DISCUSSION... THE GULF OF MEXICO... THE MOST ACTIVE WEATHER IN THE GULF THIS MORNING IS THE SCATTERED MODERATE CONVECTION IN THE SE PORTION FROM 23N-26N BETWEEN 80W-86W. ISOLATED SHOWERS AND TSTMS ARE ALSO JUST TO THE W OF THIS AREA OVER THE MIDDLE GULF...S OF 26N BETWEEN 86W-90W. CLOUD TOPS OVER THIS CONVECTION ARE BEING STRETCHED TO THE S INTO THE CARIBBEAN BY STRONG UPPER NLY FLOW BETWEEN THE UPPER LOW JUST SW OF SUBTROPICAL STORM GABRIELLE...AND RIDGING EXTENDING INTO THE GULF FROM AN UPPER HIGH OVER CENTRAL TEXAS. THE TRIGGER FOR THESE SHOWERS/TSTMS SEEMS TO BE WEAK LOW TO MID LEVEL TROUGHING. MOISTURE MAY HAVE ALSO BEEN INCREASED IN THE VICINITY FROM THE TROPICAL WAVE MOVING THROUGH THE FAR W CARIBBEAN. OTHERWISE...WEAK SFC RIDGING DOMINATES WHICH IS PRODUCING MOSTLY LIGHT WINDS/LOW SEAS ACROSS THE BASIN. SIMILAR CONDITIONS ARE GENERALLY EXPECTED TO PERSIST THROUGH THE END OF THE WEEKEND. HOWEVER...SCATTERED TSTMS ASSOCIATED WITH WEAK SFC TROUGHING IS GENERALLY EXPECTED TO PERSIST NEAR AND N OF THE YUCATAN CHANNEL. THE CARIBBEAN SEA... THE CARIBBEAN IS OVERALL PRETTY QUIET THIS MORNING. THE MAIN AREA OF CONVECTION IS THE SCATTERED MODERATE/ISOLATED STRONG IN THE SW CARIBBEAN S OF 13N BETWEEN THE COASTS OF COLOMBIA AND COSTA RICA/NICARAGUA. THIS SEEMS MOSTLY TIED TO THE ITCZ IN ADDITION TO DIFFLUENT FLOW ALOFT. TRADES ARE LIGHT TO MODERATE WITH ONLY WEAK RIDGING IN PLACE...WITH THE NORMAL PATTERN BEING DISRUPTED IN PART BY GABRIELLE IN THE WRN ATLC. THE TRADES ARE CARRYING TYPICAL PATCHES OF LOW LEVEL MOISTURE WITH EMBEDDED SHOWERS WWD...WITH A SLIGHTLY MORE CONCENTRATED AREA OF SHOWERS NOTED NEAR THE LEEWARD ISLANDS WHICH ARE IN VIEW OF THE SAN JUAN RADAR. THIS ACTIVITY IS OCCURRING DOWNSTREAM FROM A WEAK INVERTED UPPER TROUGH JUST E OF THE LEEWARD ISLANDS. THE REMAINDER OF THE UPPER PATTERN IS DOMINATED BY RIDGING OVER THE NW PORTION...WITH WLY UPPER FLOW OVER MUCH OF THE CENTRAL CARIBBEAN BETWEEN THE UPPER LOW JUST E OF CENTRAL FLORIDA AND AN UPPER HIGH OVER NRN SOUTH AMERICA. LIGHT TO MODERATE TRADES EXPECTED TO PERSIST THROUGH THE END OF THE WEEKEND...STRONGEST NEAR THE N COAST OF COLOMBIA. THE ATLANTIC OCEAN... THE WRN ATLC IS DOMINATED BY SUBTROPICAL STORM GABRIELLE. SEE SPECIAL FEATURE SECTION ABOVE FOR MORE DETAILS. SFC TROUGHING TRAILING S/SW OF GABRIELLE EXTENDS THROUGH THE SE BAHAMAS AND IS SUPPORTING THE SCATTERED SHOWERS/ISOLATED TSTMS FROM 21N-27N BETWEEN 70W-79W. THIS IS ALSO BEING SUPPORTED BY LIFT AHEAD OF THE UPPER LOW NEAR 27N78W. THE TAIL END OF A FRONTAL SYSTEM IN THE NORTH CENTRAL ATLC IS TRIGGERING ISOLATED TSTMS N OF 25N BETWEEN 40W-63W. THE ASSOCIATED DEEP LAYER LOW REMAINS WELL DEFINED NEAR 41N43W...AND HAS TROUGHING ENTERING THE AREA N OF 25N GENERALLY BETWEEN 45W-60W. WEAK RIDGING DOMINATES THE REMAINDER OF THE SFC PATTERN ACROSS THE DISCUSSION AREA...WITH A 1021 MB CENTER ANALYZED NEAR 28N31W. WINDS ARE ON THE LIGHT TO MODERATE SIDE OVER MUCH OF THE AREA E OF 65W...IN RESPONSE TO THE WEAK RIDGING IN PLACE IN ADDITION TO THE FRONT ALONG 32N43W 26N55W 29N63W WHICH IS DISRUPTING THE TRADES. THE EXCEPTION IS SLIGHTLY STRONGER NE FLOW OFF THE NW COAST OF AFRICA...PER THE USUAL STRONGER GRADIENT IN PLACE. $$ WILLIS