000 AXNT20 KNHC 022358 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED SEP 02 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 2330 UTC. ...SPECIAL FEATURES... AS OF 03/0000 UTC TROPICAL STORM ERIKA IS CENTERED NEAR 15.9N 62.0W OR JUST W OF GUADELOUPE. ERIKA HAS BEEN DRIFTING BETWEEN THE W AND WSW BUT SHOULD BEGIN TO MOVE WWD NEAR 9 KT. ESTIMATED CENTRAL PRESSURE IS 1008 MB. ERIKA BARELY REMAINS A TROPICAL STORM WITH MAXIMUM SUSTAINED WINDS OF 35 KT WITH GUSTS TO 45 KT...AND WILL LIKELY WEAKEN FURTHER TONIGHT. NUMEROUS STRONG CONVECTION IS FROM 13N-19N BETWEEN 57W-63W ALREADY AFFECTING THE LESSER ANTILLES. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 28W S OF 20N MOVING W NEAR 20 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SATELLITE IMAGERY AND SATELLITE DERIVED WINDS INDICATE LOW-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS. A DRY SAHARAN AIR LAYER ALONG WITH SAHARAN DUST IS W OF THE WAVE AXIS CONFINING CONVECTION TO THE SRN PORTION OF THE WAVE AXIS ALONG THE ITCZ FROM 8N-10N BETWEEN 24W-30W. A TROPICAL WAVE EXTENDS FROM 15N44W TO 7N41W MOVING W NEAR 18 KT. THIS WAVE REMAINS LOW-AMPLITUDE AND EMBEDDED WITHIN THE ITCZ. SATELLITE IMAGERY INDICATES AN INVERTED-V STRUCTURE IN THE LOW-LEVEL CLOUDS. THE WAVE IS EMBEDDED WITHIN A LARGE AREA OF DRY SAHARAN AIR AND DUST WHICH IS INHIBITING DEEP CONVECTION NEAR THE WAVE. A SMALL AREA OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS E OF THE WAVE AXIS FROM 10N-11N BETWEEN 41W-42W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 11N15W 10N30W 10N40W 8N47W 9N55W. A LARGE CLUSTER OF NUMEROUS STRONG CONVECTION IS AT THE AFRICAN COAST FROM 11N-17N BETWEEN 10W-18W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 7N-11N BETWEEN 14W-18W. ...DISCUSSION... GULF OF MEXICO... AS OF 2100 UTC...A STATIONARY FRONT IS ANALYZED ACROSS NRN FLORIDA FROM 29N81W CONTINUING ALONG 29N83W 27N86W BECOMING A COLD FRONT ALONG 25N87W 25N93W. A PRE-FRONTAL TROUGH IS ANALYZED AHEAD OF THE FRONT ACROSS S FLORIDA ALONG 28N80W 25N84W 23N89W. ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 200 NM AHEAD OF THE FRONT AND 75 NM BEHIND THE FRONT. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO OVER PORTIONS OF CUBA...S FLORIDA AND THE ADJACENT WATERS. CLEAR SKIES AND HIGH PRESSURE IS BUILDING IN BEHIND THE FRONT ACROSS THE NW GULF. THE FRONT IS SUPPORTED BY AN UPPER LEVEL TROUGH ACROSS THE ERN CONUS EXTENDING INTO THE GULF TO NEAR 24N90W. AN UPPER LEVEL RIDGE IS ACROSS THE SW GULF CENTERED OVER MEXICO NEAR 22N104W. UPPER LEVEL DIFFLUENCE ASSOCIATED WITH THE RIDGE IS SUPPORTING ISOLATED SHOWERS ACROSS THE SRN BAY OF CAMPECHE S OF 21N W OF 93W. EXPECT THE FRONT TO DRIFT SE BEFORE DISSIPATING THU AND FRI. CARIBBEAN SEA... AN UPPER LEVEL LOW IS OVER THE NW CARIBBEAN CENTERED NEAR 20N82W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND THE RIDGE OVER THE SW GULF IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN PENINSULA S OF 21N W OF 86W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LOW AND AN UPPER LEVEL HIGH N OF THE BAHAMAS NEAR 28N71W IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS CUBA N OF 20N BETWEEN 75W-85W....AND OVER ERN JAMAICA FROM 18N-19N BETWEEN 77W-79W. ELSEWHERE ACROSS THE CARIBBEAN...DRY AIR AND SUBSIDENCE ALOFT ARE SUPPORTING GENERALLY FAIR WEATHER EXCEPT FOR THE FAR E CARIBBEAN WHICH IS BEGINNING TO FEEL THE AFFECT OF TROPICAL STORM ERIKA...SEE SPECIAL FEATURES ABOVE. ATLANTIC OCEAN... THE MAIN FOCUS IS TROPICAL STORM ERIKA LOCATED VERY NEAR GUADELOUPE...SEE SPECIAL FEATURES ABOVE. IN THE W ATLC...AS OF 2100 UTC...A STATIONARY FRONT ENTERS THE AREA NEAR 32N77W AND EXTENDS SW TO NRN FLORIDA NEAR 29N81W AND INTO THE GULF OF MEXICO. A PRE-FRONTAL SURFACE TROUGH IS AHEAD OF THE FRONT FROM 28N80W TO THE FLORIDA COAST NEAR 28N81W CONTINUING ACROSS THE STATE INTO THE GULF. A SECOND SURFACE TROUGH IS ANALYZED OVER THE NW BAHAMAS FROM 30N77W TO 24N78W. SURFACE CONVERGENCE NEAR THESE BOUNDARIES IS SUPPORTING ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS FROM CUBA NWD OUT OF THE DISCUSSION AREA W OF 73W. THE FRONT IS SUPPORTED BY AN UPPER LEVEL TROUGH OVER THE ERN CONUS. THE AFOREMENTIONED SHOWER ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THIS UPPER TROUGH AND AN UPPER LEVEL HIGH CENTERED NEAR 28N71W. ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES ANCHORED BY A 1029 MB HIGH NEAR 36N34W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS S OF 24N BETWEEN 40W-75W IN ASSOCIATION WITH ERIKA. AN UPPER LEVEL TROUGH IS N OF 16N BETWEEN 28W-50W. A SECOND UPPER LEVEL RIDGE IS E OF 35W WITH AXIS ALONG 16N. $$ WALTON