000 AXNT20 KNHC 081803 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURE... SUBTROPICAL STORM GABRIELLE CONTINUES NORTHWESTWARD AT 8 KT TOWARD NORTH CAROLINA. TROPICAL STORM WARNINGS ARE IN EFFECT. AT 08/1800 UTC...IT IS CENTERED NEAR 31.8N 74.1W OR ABOUT 210 NM SOUTHEAST OF CAPE LOOKOUT NORTH CAROLINA. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1009 MB. MAXIMUM SUSTAINED WINDS ARE 40 KT WITH GUSTS TO 50 KT. VISIBLE IMAGERY REVEALS A FULLY EXPOSED BUT WELL-DEFINED LOW-LEVEL CENTER OF CIRCULATION. DEEP CONVECTION REMAINS CONFINED NORTH OF THE CENTER AND IS MOST ABUNDANT IN THE NORTHWESTERN QUADRANT. EVEN THOUGH THE CONVECTION IS BECOMING MORE PERSISTENT NEAR THE CENTER...THE STATUS REMAINS SUBTROPICAL GIVEN THAT THE RADIUS OF MAXIMUM WINDS REMAINS LARGE. ACCORDING TO THE OFFICIAL FORECAST TRACK...GABRIELLE WILL BRUSH OR COME ONSHORE INTO EASTERN NORTH CAROLINA AROUND SUNSET SUNDAY...THEN SHOULD MOVE FAIRLY QUICKLY BACK OUT TO SEA AND BECOME EXTRATROPICAL WED. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 27W S OF 20N. THIS MORNING BOTH...THE QUIKSCAT AND ASCAT PASS SHOWED A CYCLONIC CIRCULATION ALONG THE WAVE AXIS...AND A SFC LOW WAS INTRODUCED ON THE 12Z SFC MAP NEAR 9N. THIS WAVE IS PRODUCING A LARGE AREA OF SHOWERS AND TSTMS WITH THE STRONGEST ACTIVITY NOTED FROM 10N-14 BETWEEN 25W-29W. THIS SYSTEM HAS THE POTENTIAL FOR SOME DEVELOPMENT DURING THE NEXT FEW DAYS AS IT MOVES WESTWARD AT ABOUT 15 MPH. A TROPICAL WAVE IS ALONG 52W SOUTH OF 22N MOVING WEST NEAR 15 KT. CONVECTION HAS SLIGHTLY INCREASED ON THE NORTHERN END OF WAVE AXIS FROM 15N-19N BETWEEN 51W-56W. A 1013 MB LOW PRESSURE CENTER REMAINS E OF THE WAVE AXIS NEAR 12N46W...WHICH IS NEARLY STATIONARY. THIS LOW IS FORECAST TO DISSIPATE PRETTY SOON AND A NEW LOW COULD FORM ALONG THE WAVE AXIS NEAR 14N/15N. MOISTURE FROM THIS WAVE SHOULD AFFECT THE LEEWARD ISLANDS SUNDAY EVENING AND THE UK/US VIRGIN ISLANDS AND PUERTO RICO MON. A TROPICAL WAVE IS ALONG 86W/87W SOUTH OF 22N MOVING WEST 15 KT. THE AXIS OF THE WAVE CROSSES HONDURAS AND NICARAGUA...WHERE THERE ARE SCATTERED SHOWERS AND ISOLATED TSTMS. THE WAVE...ALONG WITH A SFC TROUGH OVER THE SE GULF OF MEXICO AND THE STRAITS OF FLORIDA IS ALSO HELPING TO INDUCE SOME CONVECTIVE ACTIVITY OVER CUBA AND THE SE GULF. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 14N17W 10N24W 7N30W 6N40W 8N50W. BESIDES FOR THE CONVECTION ASSOCIATED WITH THE E ATLC TROPICAL WAVE...SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 5N-9N BETWEEN 24W-39W. SIMILAR CONVECTION IS OVER WESTERN AFRICA FROM 10N-18N BETWEEN 7W-18W. DISCUSSION... THE GULF OF MEXICO... ABUNDANT CLOUDINESS WITH SHOWERS AND EMBEDDED TSTMS ARE NOTED OVER THE SE QUADRANT OF THE GULF. THIS ACTIVITY IS PRIMARILY ASSOCIATED WITH A SFC TROUGH THAT GOES FROM 29N86W TO 23N87W. A PAIR OF OTHER FEATURES ARE ENHANCING THIS ACTIVITY...ONE IS A TROPICAL WAVE OVER THE WESTERN CARIBBEAN AND THE SECOND ONE IS A SFC TROUGH THAT EXTENDS ACROSS THE STRAITS OF FLORIDA INTO THE SE GULF. SOME OF THE COMPUTER MODELS DEVELOP A LOW IN THIS AREA. ALOFT...AN UPPER LOW IS JUST E OF SOUTH FLORIDA PRODUCING NW WINDS OVER THE SE GULF AND W-CENTRAL CUBA. DIFFLUENCE ASSOCIATED WITH THESE WINDS ARE ALSO HELPING TO DEVELOP SHOWERS AND TSTMS OVER THE AREA. AN UPPER RIDGE DOMINATES MOST OF THE GULF OF MEXICO ANCHORED ON A HIGH OVER TEXAS. OTHERWISE...WEAK SFC RIDGING DOMINATES WHICH IS PRODUCING MOSTLY LIGHT WINDS/LOW SEAS ACROSS THE BASIN. A WEAK SFC TROUGH IS OVER THE SW GULF VERY CLOSE TO THE MEXICAN COAST. A HUMID AND UNSTABLE ENVIRONMENT WILL PERSIST OVER THE SE GULF AT LEAST DURING THE NEXT 24 HOURS. THE CARIBBEAN SEA... THE MOST ACTIVE WEATHER IS OVER THE SW CARIBBEAN WHERE SATELLITE IMAGERY SHOWS SCATTERED MODERATE/ISOLATED STRONG CONVECTION. THIS CONVECTIVE ACTIVITY IS RELATED TO THE ITCZ...A 1010 MB LOW NEAR 11N77W AND A TROPICAL WAVE ALONG 86W/78W IN ADDITION TO DIFFLUENT FLOW ALOFT. LIGHT TO MODERATE TRADE WINDS ARE BLOWING ACROSS THE BASIN...PARTICULARLY ACROSS THE SOUTH-CENTRAL CARIBBEAN WHERE A QUIKSCAT PASS FROM THIS MORNING SHOWED ELY WINDS OF 20 KT. THESE WINDS ARE CARRYING TYPICAL PATCHES OF LOW LEVEL MOISTURE WITH EMBEDDED SHOWERS WWD...WITH A SLIGHTLY MORE CONCENTRATED AREA OF SHOWERS BETWEEN THE LEEWARD ISLANDS AND PUERTO RICO...WHICH ARE IN VIEW OF THE SAN JUAN DOPPLER 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 SOUTH 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 NW BAHAMAS INTO THE STRAIT OF FLORIDA AND THE SE GULF OF MEXICO. THIS TROUGH IS SUPPORTING SCATTERED SHOWERS/ISOLATED TSTMS OVER THE AREA. A COLD FRONT ENTERS THE FORECAST AREA NEAR 31N40W...THEN CONTINUES SW AND MAINLY WEST TO 25N60W. A BAND OF SHOWERS WITH ISOLATED TSTMS IS JUST AHEAD OF THE FRONT. THE ASSOCIATED DEEP LAYER LOW REMAINS WELL DEFINED NEAR 41N44W...AND HAS TROUGHING ENTERING THE AREA N OF 25N GENERALLY BETWEEN 45W-60W. WEAK RIDGING DOMINATES THE REMAINDER OF THE SFC PATTERN WITH A 1021 MB CENTER ANALYZED NEAR 27N30W. 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 AFOREMENTIONED COLD FRONT. $$ GR