000 AXNT20 KNHC 181723 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI SEP 18 2009 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND 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 1630 UTC. ...SPECIAL FEATURES... AN AREA OF SHOWERS/THUNDERSTORMS ASSOCIATED WITH A 1010 MB LOW NEAR 13N39W CONTINUES TO BECOME BETTER ORGANIZED. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS MAINLY TO THE E OF THE LOW CENTER FROM 11N-16N BETWEEN 35W-38W. UPPER LEVEL WIND CONDITIONS REMAIN ONLY MODERATELY FAVORABLE FOR FURTHER DEVELOPMENT. THERE IS A MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HRS. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 24W/25W S OF 18N MOVING W NEAR 15 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. THERE IS ALSO AN AREA OF 85O MB VORTICITY NEAR THE WAVE AXIS DEPICTED BY THE CIMSS WAVETRAK MODEL GUIDANCE. SCATTERED MODERATE/STRONG CONVECTION IS FROM 16N-19N BETWEEN 22W-27W. TROPICAL WAVE IS ALONG 89W S OF 21N MOVING W NEAR 15 KT. THE WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE. DEEP CONVECTION IS CONFINED ONLY TO THE S PORTION OF THE WAVE IN THE E PACIFIC BASIN. HOWEVER...ISOLATED SHOWERS ARE TO THE E OF THE WAVE AXIS FROM 16N-22N. THIS ACTIVITY MAY BE MORE INFLUENCED BY UPPER LEVEL DIFFLUENCE. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 15N15W 16N23W 13N30W 9N43W 11N56W 9N63W. SCATTERED MODERATE/STRONG CONVECTION IS FROM 15N-18N BETWEEN 18W-22W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 15N-17N BETWEEN 28W-30W. ISOLATED MODERATE CONVECTION IS FROM 9N-11N BETWEEN 56W-61W. ...DISCUSSION... GULF OF MEXICO... AS OF 1500 UTC...A SURFACE TROUGH EXTENDS FROM S MISSISSIPPI NEAR 30N89W ALONG 27N92W 26N98W. SURFACE CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED SHOWERS/THUNDERSTORMS ALONG THE TROUGH AXIS. A STATIONARY FRONT LINES THE NERN GULF EXTENDING FROM OFF THE FLORIDA COAST NEAR 28N83W ALONG 30N86W 31N91W TO A 1010 MB SURFACE LOW OVER LOUISIANA NEAR 31N93W. SCATTERED SHOWERS/THUNDERSTORMS ARE AHEAD OF THE FRONT LINING THE NW COAST OF FLORIDA FROM 27N-31N BETWEEN 83W-85W. A FEW ISOLATED SHOWERS/THUNDERSTORMS ARE IN THE SW GULF S OF 22N W OF 93W. THE FRONT AND SURFACE TROUGH ARE SUPPORTED BY AN UPPER LEVEL TROUGH ACROSS MUCH OF THE CENTRAL GULF WITH AXIS ALONG 90W. AN UPPER LEVEL RIDGE CENTERED OVER MEXICO NEAR 20N102W COVERS THE FAR SW GULF. UPPER LEVEL DIFFLUENCE BETWEEN THESE FEATURES IS ENHANCING THE SHOWER ACTIVITY IN THE SW GULF. A SEPARATE UPPER LEVEL RIDGE CENTERED OVER THE WRN ATLC NEAR 29N73W EXTENDS OVER THE FAR SE GULF. UPPER LEVEL DIFFLUENCE BETWEEN THIS RIDGE AND THE UPPER LEVEL TROUGH IS ENHANCING THE SHOWER ACTIVITY NEAR THE FRONT IN THE NE GULF. CARIBBEAN SEA... ISOLATED SHOWERS/THUNDERSTORMS ARE ACROSS THE NW CARIBBEAN N OF 20N W OF 82W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL LOW COVERING MUCH OF THE CENTRAL AND W CARIBBEAN CENTERED NEAR 15N78W AND THE UPPER LEVEL RIDGE OVER THE WRN ATLC THAT EXTENDS INTO THE SE GULF. THE UPPER LEVEL LOW IS ALSO SUPPORTING ISOLATED SHOWERS/THUNDERSTORMS ACROSS THE CENTRAL CARIBBEAN FROM 11N-20N BETWEEN 70W-82W. ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE ERN CARIBBEAN FROM 13N-16N BETWEEN 63W-67W. THESE SHOWERS ARE ENHANCED BY MOIST SLY AND DIFFLUENT FLOW BETWEEN THE UPPER LEVEL LOW AND UPPER LEVEL RIDGING OVER THE E CARIBBEAN. MODERATE TRADE WINDS ARE ACROSS MUCH OF THE BASIN. EXPECT SHOWER ACTIVITY TO CONTINUE ACROSS THE WRN CARIBBEAN AS THE UPPER LEVEL LOW SHIFTS W-SW. ATLANTIC OCEAN... A SURFACE TROUGH EXTENDS FROM NEAR 31N71W TO THE NW BAHAMAS NEAR 26N77W. SURFACE CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ALONG THE TROUGH AXIS. SCATTERED SHOWERS/THUNDERSTORMS ARE S OF THE TROUGH AXIS FROM 23N-26N BETWEEN 76W-79W. A 1012 MB SURFACE LOW...REMNANTS OF FRED...IS CENTERED NEAR 25N66W. A SURFACE TROUGH EXTENDS THROUGH THE LOW CENTER FROM 28N65W TO 24N66W. SCATTERED SHOWERS/THUNDERSTORMS ARE MAINLY W OF THE LOW CENTER FROM 23N-26N BETWEEN 66W-69W. THE REMAINDER OF THE ATLC IS DOMINATED BY A BROAD SURFACE RIDGE ANCHORED BY A 1025 MB HIGH NEAR 34N46W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE DOMINATES THE WRN ATLC CENTERED NEAR 29N73W. AN UPPER LEVEL LOW LIES TO THE SE CENTERED NEAR 21N58W. UPPER LEVEL DIFFLUENCE BETWEEN THESE TWO FEATURES IS ENHANCING SHOWER ACTIVITY NEAR THE SURFACE LOW NEAR 25N66W. AN UPPER LEVEL TROUGH EXTENDS ACROSS THE NE ATLC WITH AXIS ALONG 30N22W TO 22N37W. A BROAD UPPER LEVEL RIDGE COVERS THE TROPICAL ATLC ENHANCING CONVECTION ALONG THE ITCZ. $$ WALTON