000 AXNT20 KNHC 201139 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT TUE SEP 20 2011 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1015 UTC. ...SPECIAL FEATURES... A 1008 MB LOW IS EMBEDDED ALONG THE MONSOON TROUGH AXIS NEAR 11N38W MOVING W AT 5-10 KT. TOTAL PRECIPITABLE WATER IMAGERY INDICATES THAT LOW-LEVEL MOISTURE IS MAXIMIZED FROM 07N-15N BETWEEN 31W-41W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM 09N-13N BETWEEN 35W-42W. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN CONDUCIVE FOR A TROPICAL DEPRESSION TO FORM LATER TODAY OR ON WEDNESDAY. ...TROPICAL WAVES... TROPICAL WAVE IS ANALYZED FROM 10N-18N ALONG 17W MOVING W AT 10-15 KT. VISIBLE METEOSAT-9 SATELLITE IMAGERY INDICATES A BROAD LOW TO MID-LEVEL CYCLONIC CIRCULATION HAS EMERGED OFF THE COAST OF W AFRICA. EXAMINING RECENT UPPER AIR TIME SECTION ANALYSES FROM BAMAKO MALI...THIS WAVE APPEARS TO HAVE PASSED AROUND 18/1200 UTC AND IS POISED TO FULLY PASS DAKAR SENEGAL...AT THE SURFACE AND ALOFT...THIS MORNING. DEEP CONVECTION REMAINS LIMITED WITH ISOLATED MODERATE CONVECTION FROM 12N-15N BETWEEN 17W-20W. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 14N18W TO 09N26W TO THE SPECIAL FEATURES 1008 MB LOW NEAR 11N38W TO 09N49W. WIDELY SCATTERED MODERATE CONVECTION IS FROM 04N-07N BETWEEN 22W-31W...AND FROM 06N-08N BETWEEN 36W-48W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY INDICATES AN UPPER LEVEL SHORTWAVE TROUGH IS PROGRESSING ACROSS THE OHIO AND LOWER MISSISSIPPI RIVER VALLEYS THIS MORNING WITH MOSTLY SOUTHWESTERLY FLOW ALOFT ACROSS MUCH OF THE NORTHERN GULF WATERS. THIS TROUGH SUPPORTS A COLD FRONT REMAINING NORTH OF THE GULF COAST ACROSS SE TEXAS AND NORTHERN LOUISIANA HOWEVER...A PRE-FRONTAL TROUGH EXTENDS FROM SOUTHWARD ALONG 90W TO 27N90W. LOW-LEVEL MOISTURE CONVERGENCE IN THE VICINITY OF THE TROUGH ALONG WITH MIDDLE TO UPPER LEVEL DIFFLUENCE IS GENERATING AN AREA OF WIDELY SCATTERED SHOWERS AND TSTMS N OF 28N BETWEEN 85W-90W. SE OF THE PROGRESSIVE TROUGHING...AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE SW GULF WATERS NE OVER THE FLORIDA PENINSULA AND INTO THE SW NORTH ATLC. WHILE E-SE FLOW PREVAILS ACROSS THE EASTERN GULF...LOW-TOPPED ISOLATED SHOWERS ARE OCCURRING N OF 23N E OF 90W...INCLUDING THE STRAITS OF FLORIDA. CARIBBEAN SEA... AN UPPER LEVEL SHORTWAVE TROUGH EXTENDS INTO THE WESTERN CARIBBEAN FROM THE SW NORTH ATLC WITH AXIS FROM 27N71W TO 17N83W. THIS IS PROVIDING MUCH OF THE CARIBBEAN SEA WITH NORTH TO GENERALLY WESTERLY UPPER LEVEL FLOW. WATER VAPOR IMAGERY INDICATES MUCH OF THIS FLOW IS MODERATELY DRY ALOFT WITH VERY FEW SHOWERS OCCURRING THIS MORNING S OF A LINE FROM THE YUCATAN CHANNEL NEAR 22N86W TO 12N72W. NORTH OF THIS LINE HOWEVER...A SURFACE TROUGH IS ANALYZED FROM WESTERN CUBA NEAR 22N84W TO SOUTH OF JAMAICA NEAR 15N77W. ISOLATED SHOWERS AND TSTMS ARE PRIMARILY OCCURRING NORTH OF THIS BOUNDARY WHERE LOW-LEVEL MOISTURE CONVERGENCE IS MAXIMIZED. THIS CONVECTIVE ACTIVITY IS MOSTLY SOUTH OF CUBA AND N OF 16N BETWEEN 70W-82W. FARTHER EAST...CONTINUED UPPER LEVEL TROUGHING OVER THE SW NORTH ATLC EXTENDS SOUTHWARD INTO THE NE CARIBBEAN AND IS PROVIDING FOR THE ADVECTION OF TROPICAL MOISTURE NORTHWARD ACROSS HISPANIOLA... PUERTO RICO...AND THE LEEWARD ISLAND. ISOLATED SHOWERS AND TSTMS ARE OCCURRING N OF 14N E OF 70W. THE UPPER LEVEL TROUGHING AND SUBSEQUENT UPPER LEVEL DIFFLUENT FLOW EAST OF THE TROUGH AXIS IS FORECAST TO REMAIN IN PLACE ACROSS THE WESTERN CARIBBEAN THROUGH THURSDAY MORNING...WITH THE INCREASED POSSIBILITY OF WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS OVER HISPANIOLA AND PUERTO RICO THROUGH THE REMAINDER OF THE WEEK. ATLANTIC OCEAN... AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE EASTERN GULF OF MEXICO OVER THE FLORIDA PENINSULA INTO THE SW NORTH ATLC TO BEYOND 32N76W. EAST TO SOUTHEASTERLY LOW-LEVEL FLOW HOWEVER STILL REMAINS CONVERGENT OVER THE FAR W ATLC WITH ISOLATED SHOWERS AND TSTMS OCCURRING N OF 29N W OF 76W. FARTHER EAST OVER THE REMAINDER OF THE W ATLC...AN UPPER LEVEL TROUGH AXIS EXTENDS FROM 32N68W TO EASTERN CUBA NEAR 21N77W AND INTO THE WESTERN CARIBBEAN SEA. EAST OF THE UPPER LEVEL TROUGH AXIS...MIDDLE TO UPPER LEVEL TROPICAL MOISTURE CONTINUES TO ADVECT NORTHWARD BETWEEN 56W-74W. WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING FROM 17N-29N BETWEEN 58W-75W. THE REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE OF A SURFACE RIDGE N OF 20N E OF 55W ANCHORED BY A 1023 MB HIGH CENTERED SE OF THE AZORES NEAR 36N21W. EMBEDDED WITHIN THE SW PERIPHERY OF THIS SURFACE RIDGE...A WEAK 1012 MB SURFACE LOW IS CENTERED NEAR 18N53W AND CONTINUES TO DRIFT WESTWARD. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 120 NM OF THE CENTER OF THE LOW. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN