000 AXNT20 KNHC 211756 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON SEP 21 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 1715 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 32W S OF 13N MOVING W NEAR 15 KT. VISIBLE SATELLITE IMAGERY SHOWS CYCLONIC TURNING IN THE LOW-LEVEL CLOUD FIELD IN THE VICINITY OF THE WAVE AXIS. AN EARLIER ASCAT PASS AROUND 21/1200 UTC ALSO CONFIRMED THE PRESENCE OF THE LOW AMPLITUDE WAVE. OF NOTE...A LARGE AREA OF SAHARAN DUST FOLLOWS THE WAVE AND IS LOCATED MAINLY E OF 30W. ISOLATED SHOWERS ARE FROM 10N-19N BETWEEN 31W-35W. TROPICAL WAVE EXTENDS FROM 14N44W TO 21N41W MOVING WNW NEAR 15 KT. THE WAVE IS BEING GUIDED WNW AROUND A 1012 MB LOW THAT IS CENTERED NEAR 15N48W. THE ENTIRE AREA SURROUNDING THE WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE AS OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY AND AN EARLIER QUIKSCAT PASS AROUND 21/0900 UTC DEPICTED BROAD LOW-LEVEL CYCLONIC CURVATURE EXTENDING FROM THE LOW TO THE NE NEAR THE WAVE AXIS. THIS LOW-LEVEL CURVATURE AND SURFACE CONVERGENCE IS GENERATING SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 16N-23N BETWEEN 39W-44W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 10N15W 7N30W 8N34W 8N60W. SCATTERED MODERATE CONVECTION IS WITHIN FROM 4N-8N BETWEEN 20W-27W. ...DISCUSSION... GULF OF MEXICO... UPPER LEVEL ANTICYCLONIC FLOW COVERS A MAJORITY OF THE GULF AS AN UPPER LEVEL HIGH IS CENTERED OVER CENTRAL MEXICO NEAR 20N100W. AN UPPER LEVEL RIDGE EXTENDS FROM THE HIGH NE THROUGH 25N90W TO THE BIG BEND REGION OF FLORIDA. AT THE SURFACE... GENERALLY LIGHT 10-15 KT SE WINDS ARE OBSERVED AS A SURFACE RIDGE LIES FROM THE SE CONUS SW TO OVER E/CENTRAL MEXICO NEAR VERACRUZ. A FEW ISOLATED SHOWERS AND TSTMS ARE OVER THE NE GULF AND ARE FOUND N OF 26N BETWEEN 85W-91W DUE IN PART TO LOW-LEVEL SURFACE WIND CONVERGENCE AND AIDED BY UPPER LEVEL DIFFLUENCE FROM THE UPPER RIDGING ALOFT. THE SURFACE RIDGE IS EXPECTED TO HOLD IN PLACE THROUGH WEDNESDAY ACROSS MUCH OF THE CENTRAL AND ERN GULF...HOWEVER A COLD FRONT IS FORECAST TO ENTER THE NW GULF WATERS LATE WEDNESDAY. CARIBBEAN SEA... THE NW CARIBBEAN IS INFLUENCE BY A MIDDLE TO UPPER LEVEL TROUGH WITH AXIS ALONG 90W ACROSS THE YUCATAN PENINSULA...BELIZE AND GUATEMALA. THIS TROUGHING IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS ACROSS THE NW CARIBBEAN N OF 16N W OF 80W...WITH THE MOST CONCENTRATED ACTIVITY ON SATELLITE IMAGERY OVER BELIZE AND THE ERN YUCATAN PENINSULA. AN UPPER LEVEL RIDGE IS LOCATED E OF THE UPPER TROUGH ALONG 82W WITH THE ASSOCIATED UPPER LEVEL DIFFLUENCE PRODUCING SCATTERED SHOWERS ALONG THE COASTAL WATERS OF NICARAGUA...COSTA RICA AND PANAMA. THE CLOSE PROXIMITY OF THE ITCZ AXIS ALONG 9N OVER PANAMA IS ALSO AIDING IN THE ACTIVITY OVER SRN PORTIONS OF CENTRAL AMERICA. THE REMAINDER OF THE CARIBBEAN E OF 78W IS COVERED BY AN UPPER LEVEL TROUGH AND CYCLONIC CURVATURE ALOFT. MODERATE SUBSIDENCE IS EVIDENT ON WATER VAPOR IMAGERY ACROSS THE ERN CARIBBEAN...HOWEVER ISOLATED SHOWERS OVER THE N/CENTRAL CARIBBEAN N OF 15N BETWEEN 66W-75W. MODERATE TO FRESH TRADE WINDS CONTINUE ACROSS MOST OF THE BASIN AS DEPICTED BY AN EARLIER QUIKSCAT PASS AROUND 21/1100 UTC...WITH 20-25 KT WINDS NOTED ALONG THE COAST OF COLOMBIA S OF 14N BETWEEN 72W-77W. ATLANTIC OCEAN... THE UPPER LEVEL RIDGING LOCATED ACROSS THE GULF OF MEXICO EXTENDS ACROSS NRN FLORIDA AND INTO THE FAR W ATLC W OF 75W. UPPER LEVEL DIFFLUENCE IS CONTINUING TO GENERATE ISOLATED SHOWERS AND TSTMS W OF 78W AND TO OVER THE ERN FLORIDA PENINSULA. FARTHER EAST...AN UPPER LEVEL SHORTWAVE TROUGH...PART OF A LARGER UPPER LEVEL TROUGH REGIME OVER THE CENTRAL ATLC... SUPPORTS A SURFACE TROUGH THAT EXTENDS FROM 28N75W THROUGH A 1017 MB LOW CENTERED NEAR 30N73W TO 32N69W. SCATTERED SHOWERS AND TSTMS ARE OCCURRING FROM 28N-32N BETWEEN 70W-75W. THIS SURFACE TROUGH IS NEAR THE TAIL END OF A STATIONARY FRONT THAT IS DRAPED ALONG 33N BETWEEN 55W-72W. LOW-LEVEL CONVERGENCE S OF THE FRONT COUPLED WITH UPPER LEVEL DIFFLUENCE DUE TO LARGE SCALE TROUGHING ACROSS THE NW ATLC IS GENERATING SCATTERED SHOWERS AND TSTMS FROM 29N TO BEYOND 32N BETWEEN 58W-65W. ELSEWHERE... SCATTERED SHOWERS ARE WITHIN 120 NM EITHER SIDE OF THE STATIONARY FRONT. AN UPPER LEVEL LOW IS CENTERED NEAR 25N58W WITH THE TROUGH AXIS EXTENDING S ALONG 60W AND NEAR THE LESSER ANTILLES. UPPER LEVEL DIFFLUENCE LOCATED E OF THE TROUGH AXIS IS GENERATING SCATTERED SHOWERS AND TSTMS FROM 17N-22N BETWEEN 54W-59W. ANOTHER EMBEDDED SHORTWAVE TROUGH IS LOCATED NEAR 20N50W AND IS ALSO PRODUCING AN AREA OF SCATTERED SHOWERS AND TSTMS FROM 19N-22N BETWEEN 46W-51W. THE REMAINDER OF THE ATLC REMAINS FAIRLY CALM UNDER THE INFLUENCE OF A BROAD SURFACE RIDGE N OF 25N E OF 55W ANCHORED BY A 1025 MB HIGH CENTERED NEAR 34N42W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS BETWEEN 35W-45W...E OF THE AFOREMENTIONED UPPER LOW N-NE OF THE LESSER ANTILLES. ANOTHER UPPER LEVEL LOW DOMINATES THE NE PORTION OF THE ATLC DISCUSSION AREA CENTERED NEAR 30N27W. IN THE TROPICAL ATLC...AN UPPER LEVEL RIDGE DOMINATES E OF 40W ENHANCING THE CONVECTION NEAR THE TROPICAL WAVE IN THE CENTRAL ATLC. $$ HUFFMAN