000 AXNT20 KNHC 031758 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU SEP 03 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. ...SPECIAL FEATURES... TROPICAL STORM ERIKA IS CENTERED NEAR 16.6N 64.7W AT 03/1800 UTC OR ABOUT 70 NM S OF ST. CROIX AND ABOUT 135 NM SE OF SAN JUAN PUERTO RICO MOVING W AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS FROM 13N-19N BETWEEN 60W-64W. 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... TROPICAL WAVE IS ALONG 17W S OF 16N MOVING W NEAR 15 KT. A 1012 MB LOW IS ALONG THE WAVE AXIS NEAR 11N AND HAS BEEN TRACKING TO THE WNW OVER THE PAST 24 HOURS. UPPER AIR TIME SECTION ANALYSES FROM BAMAKO MALI DEPICTED THAT THIS WAVE PASSED AROUND 02/1200 UTC WITH A STRONG ANOMALOUS WIND SHIFT SIGNATURE FROM THE SURFACE TO 500 MB...INDICATIONS OF A VIGOROUS AND DEEP LAYERED TROPICAL WAVE. VISIBLE SATELLITE AND CIMSS WAVETRAK MODEL GUIDANCE SHOW BROAD CYCLONIC TURNING ALONG THE WAVE AXIS BETWEEN 12W-24W. SCATTERED MODERATE CONVECTION IS FROM 6N-12N BETWEEN 13W-24W WITH SCATTERED SHOWERS COVERING A LARGER AREA FROM 6N-17N BETWEEN 12W-25W. TROPICAL WAVE IS ALONG 32W S OF 19N MOVING W NEAR 15 KT. A 1014 MB LOW IS ALONG THE WAVE AXIS NEAR 14N. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY...HOWEVER...VISIBLE SATELLITE IMAGERY INDICATES A DRY SAHARAN AIR LAYER SURROUNDING THE WAVE...THUS INHIBITING ANY SIGNIFICANT DEEP CONVECTION. MOST SCATTERED SHOWERS AND WIDELY SCATTERED MODERATE CONVECTION ARE EMBEDDED WITHIN THE ITCZ FROM 5N-11N BETWEEN 26W-36W. TROPICAL WAVE IS ALONG 47W S OF 15N MOVING W 10-15 KT. THE WAVE REMAINS LOW-AMPLITUDE AND EMBEDDED WITHIN THE ITCZ AT THE LEADING EDGE OF A MOISTURE MAXIMUM AS INDICATED BY THE TPW IMAGERY. CONVECTION IS LIMITED TO ISOLATED SHOWERS FROM 11N-14N BETWEEN 45W-49W. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 10N18W 10N30W 9N33W 9N44W 8N48W 8N60W. ASIDE FROM THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES IN THE TROPICAL ERN ATLC...SCATTERED MODERATE CONVECTION IS WITHIN 90 NM ON EITHER SIDE OF THE AXIS BETWEEN 38W-44W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL TROUGH COVERS THE ERN CONUS AND DIPS SWD INTO THE GULF WITH AN AXIS ALONG 87W TO THE YUCATAN CHANNEL. THIS UPPER TROUGH SUPPORTS A 1012 MB SURFACE LOW CENTERED IN THE NE GULF NEAR 27N86W. A SURFACE TROUGH EXTENDS ACROSS THE CENTRAL FLORIDA PENINSULA INTO THIS SURFACE LOW AND CONTINUES SW FROM THE LOW ALONG 24N87W TO 22N92W. LOW-LEVEL CONVERGENCE NEAR THE SURFACE LOW AND MIDDLE TO UPPER LEVEL LIFT ASSOCIATED WITH THE UPPER LEVEL TROUGH ARE GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS ACROSS THE NE GULF N OF 25N E OF 88W AND ALSO WITHIN 120 NM OF THE SURFACE TROUGH ACROSS THE SRN GULF. AN UPPER RIDGE IS ANCHORED IN THE E PACIFIC AND EXTENDS ACROSS CENTRAL MEXICO AND THE ERN BAY OF CAMPECHE. SCATTERED SHOWERS AND ISOLATED TSTMS ARE ACROSS THE SW GULF AND BAY OF CAMPECHE SW OF A LINE FROM 24N98W TO 20N92W. A WEAK SURFACE RIDGE IS ALONG THE NW GULF COAST AND CONTINUES TO BE SUPPORTED BY NWLY FLOW AND A DRY... SUBSIDENT AIRMASS ALOFT ON THE WRN EXTENT OF THE UPPER TROUGH ALONG 88W. GENERALLY FAIR WEATHER IS ASSOCIATED WITH THIS FEATURE ACROSS THE NW GULF. CARIBBEAN SEA... A MAIN CONCERN IS TROPICAL STORM ERIKA OVER THE LESSER ANTILLES AND NE CARIBBEAN. THE CONVECTION ASSOCIATED WITH ERIKA IS SUPPORTED ALOFT BY UPPER LEVEL DIVERGENCE PROVIDED BY AN UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED NEAR 14N65W. THE UPPER LEVEL RIDGE COVERS MUCH OF THE ERN CARIBBEAN E OF 72W. FARTHER TO THE W...THE UPPER LEVEL TROUGH IMPACTING THE GULF OF MEXICO EXTENDS THROUGH THE YUCATAN CHANNEL TO 14N80W WITH A WEAK UPPER LEVEL LOW E OF THE MAIN TROUGH AXIS CENTERED NEAR 20N74W. MOSTLY DRY AIR ALOFT AND THE REMAINS OF A SAHARAN AIR LAYER MOVING ACROSS THE WRN CARIBBEAN IS KEEPING RELATIVELY CLEAR SKIES N OF 12N W OF 72W. HOWEVER...A FEW SCATTERED SHOWERS AND ISOLATED TSTMS ARE NOTED ON SATELLITE IMAGERY IN THE SW CARIBBEAN S OF 12N AND ACROSS PANAMA...AS WELL AS A FEW ISOLATED SHOWERS OVER THE NW CARIBBEAN AS THE SURFACE TROUGH ACROSS THE S/CENTRAL GULF OF MEXICO CONTINUES DRIFTING SEWD. ATLANTIC OCEAN... A 1013 MB LOW IS CENTERED IN THE W ATLC NEAR 32N76W WITH A SURFACE TROUGH EXTENDING SW TO VERO BEACH FLORIDA AND INTO THE NE GULF OF MEXICO. SCATTERED SHOWERS ARE WITHIN 90 NM EITHER SIDE OF THE SURFACE TROUGH. ANOTHER SURFACE TROUGH EXTENDS FROM 25N77W TO 31N75W. SCATTERED SHOWERS AND TSTMS ARE FROM 22N-32N BETWEEN 72W-79W. STRONG MIDDLE TO UPPER LEVEL MOIST SLY FLOW ALOFT AND UPPER DIFFLUENCE IS FURTHER ENHANCING THE CONVECTION ACROSS THE W ATLC. TO THE EAST OF THIS ACTIVITY...A BROAD UPPER LEVEL RIDGE COVERS THE REMAINDER OF THE W ATLC ANCHORED NEAR 31N69W. A UPPER LEVEL LOW IS CENTERED NEAR 26N60W. UPPER LEVEL DIFFLUENCE E OF THE UPPER LOW IS GENERATING SCATTERED SHOWERS FROM 24N-29N BETWEEN 50W-56W. THE REMAINDER OF THE CENTRAL AND ERN ATLC IS DOMINATED BY RATHER BENIGN UPPER LEVEL FEATURES AND A BROAD SURFACE RIDGE N OF 22N W OF 70W. THIS SURFACE RIDGE IS ANCHORED BY A 1026 MB HIGH N OF THE REGION CENTERED NEAR 33N42W. $$ HUFFMAN