000 AXNT20 KNHC 041800 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI SEP 04 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... A TROPICAL WAVE EXTENDS FROM 9N24W THROUGH A 1012 MB LOW NEAR 12N24W TO 20N21W MOVING W NEAR 18 KT. VISIBLE SATELLITE IMAGERY INDICATES AN ELONGATED LOW-LEVEL CYCLONIC CIRCULATION FOCUSED NEAR THE SURFACE LOW WITH CIMSS WAVETRAK MODEL GUIDANCE INDICATING A 850-500 MB LAYER OF CYCLONIC CURVATURE BETWEEN 20W-30W. THE WAVE REMAINS WITHIN A MAXIMUM AREA OF DEEP LAYER MOISTURE AS INDICATED BY THE TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE CONVECTION IS FROM 7N-15N BETWEEN 23W-29W. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 35W S OF 19N WITH A 1013 MB LOW ALONG THE WAVE NEAR 14N MOVING W NEAR 12 KT. THE WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. HOWEVER...VISIBLE SATELLITE IMAGERY INDICATES SAHARAN DUST IS LOCATED TO THE W OF THE WAVE AXIS AND ALSO TO THE NE OF SURFACE LOW. THIS SAHARAN AIR LAYER IS INHIBITING ANY SIGNIFICANT DEEP CONVECTION WITH ONLY A SMALL AREA OF SCATTERED MODERATE CONVECTION FROM 15N-17N BETWEEN 34W-37W. TROPICAL WAVE IS ALONG 53W S OF 16N MOVING W NEAR 15 KT. THE WAVE REMAINS RELATIVELY LOW-AMPLITUDE WITH A WEAKENING 850 MB VORTICITY SIGNATURE IN THE CIMSS WAVETRAK MODEL GUIDANCE OVER THE PAST 6-12 HOURS. SAHARAN DUST REMAINS TO THE E OF THE WAVE AXIS AND THUS LIMITING ANY CONVECTION. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 14N16W 13N21W 11N26W 9N34W 8N37W 8N51W. CLUSTERS OF WIDELY SCATTERED MODERATE CONVECTION AND SCATTERED SHOWERS ARE WITHIN 120 NM S OF THE ITCZ BETWEEN 33W-52W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL TROUGH COVERS THE ERN CONUS AND EXTENDS TROUGHING OVER THE CENTRAL AND ERN GULF OF MEXICO SWD TO THE YUCATAN PENINSULA AND CHANNEL. EMBEDDED WITHIN THE UPPER LEVEL TROUGHING IS AN UPPER LOW CENTERED NEAR 26N85W. THESE UPPER LEVEL FEATURES SUPPORT A SURFACE TROUGH THAT EXTENDS ACROSS THE SRN FLORIDA PENINSULA AND ENTERS THE GULF NEAR FORT MYERS ALONG 27N87W TO 25N92W. LOW-LEVEL CONVERGENCE S OF THE SURFACE TROUGH AND MOIST SWLY UPPER LEVEL DIVERGENT FLOW ARE GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS OVER THE SE GULF FROM 21N-25N BETWEEN 82W-24W. ANOTHER SURFACE TROUGH IS ANALYZED ACROSS THE N/CENTRAL GULF FROM SERN LOUISIANA INTO THE OFFSHORE GULF WATERS NEAR 28N90W. LOW-LEVEL CONVERGENCE E OF THE SURFACE TROUGH IS GENERATING SCATTERED SHOWERS AND TSTMS N OF 27N BETWEEN 83W-90W. THE REMAINDER OF THE GULF IS BENEATH NW TO NLY FLOW ALOFT LIMITING ANY DEEP CONVECTION...HOWEVER A FEW PASSING ISOLATED SHOWERS ARE POSSIBLE W OF 90W AND ACROSS THE BAY OF CAMPECHE. CARIBBEAN SEA... THE REMNANT 1010 MB LOW OF ERIKA IS CENTERED SOUTH OF THE MONA PASSAGE NEAR 17N68W AND IS CONTINUING TO GENERATE SCATTERED SHOWERS AND TSTMS FROM 12N-19N BETWEEN 61W-67W INCLUDING THE LEEWARD ISLANDS...VIRGIN ISLANDS AND PUERTO RICO. THE UPPER LEVEL TROUGH OVER THE ERN GULF OF MEXICO COVERS THE NW CARIBBEAN N OF 16N W OF 70W GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS NW OF LINE FROM NW HONDURAS NEAR 16N88W TO WRN CUBA NEAR 22N82W. AN UPPER LEVEL ANTICYCLONIC CIRCULATION COVERS THE REMAINDER OF THE CARIBBEAN WITH THE UPPER HIGH ANCHORED NEAR 14N70W DRAWING TROPICAL MOISTURE OVER THE SW CARIBBEAN AND COUPLED WITH UPPER LEVEL DIFFLUENCE IS GENERATING SCATTERED SHOWERS AND TSTMS S OF 15N W OF 76W...INCLUDING PORTIONS OF PANAMA...COSTA RICA AND NICARAGUA. ATLANTIC OCEAN... A SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR 32N78W EXTENDING SW TO A 1014 MB LOW OFF THE COAST OF ST. AUGUSTINE FLORIDA CONTINUING ACROSS THE SRN FLORIDA PENINSULA AND INTO THE GULF OF MEXICO. A BROAD UPPER RIDGE REMAINS ANCHORED OVER THE W ATLC NEAR 34N60W THAT EXTENDS UPPER LEVEL RIDGING TO THE NW BAHAMAS. BETWEEN THIS RIDGE AND THE UPPER LEVEL LOW AND TROUGHING ACROSS THE ERN GULF OF MEXICO...UPPER LEVEL DIFFLUENCE IS GENERATING CLUSTERS OF SCATTERED SHOWERS AND TSTMS FROM 23N TO BEYOND 32N BETWEEN 76W-80W. A NARROW AND ELONGATED UPPER LEVEL TROUGH IS OVER THE CENTRAL ATLC. MOIST SWLY UPPER LEVEL FLOW S OF THE TROUGH AXIS AND UPPER LEVEL DIFFLUENCE IN THE VICINITY OF THE UPPER TROUGH IS PRODUCING AN AREA OF SCATTERED SHOWERS WITHIN 150 NM OF A LINE FROM 28N60W TO 22N52W. ELSEWHERE ACROSS THE REMAINDER OF THE CENTRAL AND ERN ATLC...A BROAD SURFACE RIDGE IS N OF 22N E OF 70W PROVIDES GENERALLY FAIR WEATHER. THE SURFACE RIDGE IS ANCHORED BY A 1024 MB HIGH CENTERED NEAR 31N51W AND ANOTHER 1027 MB HIGH CENTERED S OF THE AZORES NEAR 37N29W. $$ HUFFMAN