000 AXNT20 KNHC 182348 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...SPECIAL FEATURES... AN AREA OF SHOWERS AND TSTMS ASSOCIATED WITH A 1008 MB LOW NEAR 13N40W CONTINUES TO BECOME BETTER ORGANIZED. SCATTERED MODERATE/ ISOLATED STRONG CONVECTION IS MAINLY TO THE E OF THE LOW CENTER FROM 12N-17N BETWEEN 35W-42W. 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 25W S OF 18N MOVING W NEAR 15 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY AS WELL AS A MAXIMUM IN 85O MB VORTICITY NEAR THE WAVE AXIS FROM 10N-16N BETWEEN 20W-27W AS DEPICTED BY THE CIMSS WAVETRAK MODEL GUIDANCE. SCATTERED MODERATE CONVECTION IS FROM 14N-19N BETWEEN 19W-28W. TROPICAL WAVE IS ALONG 90W S OF 21N MOVING W NEAR 15 KT. THE WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE ACROSS A LARGE PORTION OF CENTRAL AMERICA AND SRN MEXICO. THIS DEEP LAYER MOISTURE...ATMOSPHERIC INSTABILITY AND FORCING DUE TO THE WAVE IS GENERATING SCATTERED MODERATE TO STRONG CONVECTION OVER THE YUCATAN PENINSULA AND PORTIONS OF GUATEMALA FROM 16N-22N BETWEEN 87W-91W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 15N17W 15N24W 13N27W 14N36W 10N41W 9N62W. TOTAL PRECIPITABLE WATER IMAGERY INDICATES A LARGE AREA OF MAXIMUM VALUES ACROSS THE ERN TROPICAL ATLC FROM 9N-20N BETWEEN THE W AFRICA COAST AND 40W. THIS AREA...INCLUDES THE ITCZ AXIS AND SCATTERED SHOWERS AND POSSIBLE ISOLATED MODERATE CONVECTION ARE N OF 10N TO 20N E OF 40W. ELSEWHERE...SCATTERED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 56W-62W. ...DISCUSSION... GULF OF MEXICO... AS OF 2100 UTC...A SURFACE TROUGH EXTENDS INTO THE GULF OF MEXICO FROM ERN LOUISIANA NEAR 29N90W ALONG 27N92W 26N97W. LOW-LEVEL CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THE BOUNDARY. A WARM FRONT LIES INLAND OVER THE SE CONUS ALONG 31N EXTENDING FROM A 1012 MB LOW CENTERED OVER SWRN MISSISSIPPI AND IS PROVIDING THE ERN GULF WITH MAINLY WEAK SOUTHERLY SURFACE FLOW OF 5-10 KT. ISOLATED SHOWERS ARE OVER THE ERN GULF N OF 23N E OF 90W. THIS LOW PRESSURE SYSTEM AND SURFACE BOUNDARIES ARE SUPPORTED ALOFT BY AN UPPER LEVEL TROUGH WITH AXIS ALONG 90W ACROSS MUCH OF THE CENTRAL GULF. AN UPPER LEVEL RIDGE CENTERED OVER E/CENTRAL MEXICO NEAR 20N99W COVERS THE SW GULF AND BAY OF CAMPECHE. UPPER LEVEL DIFFLUENCE IS ENHANCING AN AREA OF SCATTERED SHOWERS AND ISOLATED TSTMS S OF 26N W OF 95W. ANOTHER UPPER LEVEL RIDGE IS CENTERED OVER THE NW BAHAMAS NEAR 26N78W AND EXTENDS ACROSS THE FAR SE GULF. UPPER LEVEL DIFFLUENCE BETWEEN THIS RIDGE AND THE UPPER LEVEL TROUGH IS ENHANCING SCATTERED SHOWERS AND TSTMS ACROSS THE FAR SWRN FLORIDA PENINSULA AND ADJACENT COASTAL WATERS N OF THE FLORIDA KEYS. CARIBBEAN SEA... SCATTERED SHOWERS AND TSTMS ARE OCCURRING ACROSS THE YUCATAN PENINSULA FROM 16N-22N BETWEEN 87W-91W DUE TO THE TROPICAL WAVE ALONG 90W. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL DIFFLUENCE AS THE CONVECTION MOVES WWD AND UNDER THE INFLUENCE OF AN UPPER LEVEL HIGH CENTERED OVER E/CENTRAL MEXICO. UPPER LEVEL RIDGING EXTENDS ACROSS THE YUCATAN PENINSULA OVER CUBA AND INTO THE W ATLC PROVIDING AN UPPER LEVEL DIFFLUENT ENVIRONMENT FOR SCATTERED SHOWERS AND TSTMS ACROSS CUBA AND PORTIONS OF THE NW CARIBBEAN N OF 18N. AN UPPER LEVEL LOW IS CENTERED FARTHER TO THE SE OVER THE SW CARIBBEAN NEAR 13N80W. THIS UPPER LEVEL LOW IS SUPPORTING AREAS OF SCATTERED SHOWERS AND TSTMS ACROSS PORTIONS OF SW HISPANIOLA EXTENDING TO JAMAICA AND OVER PORTIONS OF HONDURAS AND NICARAGUA. ON THE ERN PERIPHERY OF THE UPPER LEVEL LOW ACROSS THE CENTRAL CARIBBEAN MOIST SOUTHERLY DIFFLUENT FLOW IS NOTED ON WATER VAPOR IMAGERY AND IS GENERATING ISOLATED SHOWERS AND POSSIBLE ISOLATED TSTMS ACROSS THE ERN CARIBBEAN E OF 72W. MODERATE TRADE WINDS CONTINUE ACROSS MUCH OF THE BASIN AS A RELATIVELY WEAK PRESSURE GRADIENT REMAINS IN PLACE. ATLANTIC OCEAN... A SURFACE TROUGH EXTENDS FROM NEAR 31N72W ACROSS THE NW BAHAMAS TO NEAR 23N80W. LOW-LEVEL CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED SHOWERS AND POSSIBLE TSTMS WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. TO THE NORTH...A STATIONARY FRONT EXTENDS FROM N OF THE DISCUSSION AREA TO 32N72W WWD TO THE GEORGIA COAST. MOST SHOWER ACTIVITY ASSOCIATED WITH THE FRONT HOWEVER IS LOCATED N OF 32N BETWEEN 70W-82W. FARTHER SE...A SURFACE TROUGH IS ANALYZED FROM 28N66W THROUGH A 1013 MB LOW...THE REMNANTS OF FRED...TO 23N68W. SCATTERED SHOWERS AND ISOLATED TSTMS ARE WITHIN 120 NM EITHER SIDE OF THE TROUGH AXIS. MOST OF THIS ACTIVITY ACROSS THE W ATLC IS SUPPORTED ALOFT BY UPPER DIFFLUENCE ASSOCIATED WITH AN UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED OVER THE NW BAHAMAS NEAR 26N78W. THE REMAINDER OF THE CENTRAL AND ERN ATLC IS DOMINATED BY A BROAD SURFACE RIDGE ANCHORED BY A 1024 MB HIGH NEAR 33N43W AND A 1023 MB HIGH NEAR 34N19W. IN THE UPPER LEVELS...AN UPPER LEVEL LOW IS CENTERED NEAR 21N63W. LIFT AND INSTABILITY IN THE VICINITY OF THE LOW IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS FROM 18N-22N BETWEEN 60W-66W. AN UPPER LEVEL TROUGH EXTENDS ACROSS THE NE ATLC WITH AXIS ALONG 30N21W TO 22N37W. $$ HUFFMAN