000 AXNT20 KNHC 200551 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0515 UTC. ...SPECIAL FEATURES... A 1008 MB LOW IS EMBEDDED ALONG THE MONSOON TROUGH AXIS NEAR 11N37W MOVING W AT 5-10 KT. TOTAL PRECIPITABLE WATER IMAGERY INDICATES THAT LOW-LEVEL MOISTURE IS MAXIMIZED FROM 07N-15N BETWEEN 34W-43W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM 07N-15N BETWEEN 33W-42W. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR THE DEVELOPMENT OF A TROPICAL DEPRESSION DURING THE NEXT COUPLE OF DAYS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 19N16W TO 10N26W TO THE SPECIAL FEATURES 1008 MB LOW NEAR 11N37W TO 12N44W. WIDELY SCATTERED MODERATE CONVECTION IS FROM 04N-11N BETWEEN 16W-29W...AND FROM 07N-10N BETWEEN 43W-49W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY INDICATES AN UPPER LEVEL SHORTWAVE TROUGH IS PROGRESSING ACROSS THE MIDDLE AND LOWER MISSISSIPPI RIVER VALLEY THIS EVENING 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 EASTERN TEXAS AND NW LOUISIANA HOWEVER...A PRE-FRONTAL TROUGH EXTENDS FROM SE LOUISIANA NEAR 30N91W TO 27N92W. LOW-LEVEL MOISTURE CONVERGENCE IN THE VICINITY OF THE TROUGH ALONG WITH MIDDLE TO UPPER LEVEL DIFFLUENCE IS GENERATING AN AREA OF ISOLATED SHOWERS AND TSTMS WITHIN 90 NM EAST OF THE BOUNDARY...WITH DOPPLER RADAR IMAGERY INDICATING THE STRONGEST CONCENTRATION OF ACTIVITY OVER MOBILE BAY. 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. CONVECTIVE DEBRIS MOISTURE CONTINUES SPILLING OVER THE CREST OF THE RIDGE WITH MOST MOISTURE LEFTOVER FROM PRIOR AFTERNOON CONVECTION ACROSS THE FLORIDA PENINSULA. WHILE EASTERLY FLOW PREVAILS ACROSS THE EASTERN GULF... LOW-TOPPED ISOLATED SHOWERS ARE OCCURRING S OF 26N E OF 84W... 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 26N72W TO 16N84W. 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 EVENING S OF A LINE FROM THE YUCATAN CHANNEL NEAR 22N86W TO 12N71W. NORTH OF THIS LINE HOWEVER...A SURFACE TROUGH IS ANALYZED FROM WESTERN CUBA NEAR 23N81W TO SOUTH OF JAMAICA NEAR 16N77W. ISOLATED SHOWERS AND TSTMS ARE PRIMARILY OCCURRING NORTH OF THIS BOUNDARY WHERE LOW-LEVEL MOISTURE CONVERGENCE IS MAXIMIZED. THIS CONVECTIVE ACTIVITY IS PRIMARILY SOUTH OF CUBA AND N OF 16N BETWEEN 70W-83W. 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 THIS EVENING. MOST OF THE STRONGEST CONVECTIVE ACTIVITY HAS MOVED NE OF PUERTO RICO OVER THE PAST 6 HOURS...HOWEVER...ISOLATED SHOWERS ARE OCCURRING N OF 13N E OF 68W. 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 32N77W. EASTERLY LOW-LEVEL FLOW HOWEVER STILL REMAINS CONVERGENT OVER THE FAR W ATLC WITH ISOLATED SHOWERS OCCURRING N OF 26N W OF 70W. FARTHER EAST OVER THE REMAINDER OF THE W ATLC...AN UPPER LEVEL TROUGH AXIS EXTENDS FROM 32N69W 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-73W. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 90 NM EITHER SIDE OF A LINE FROM 17N63W TO 21N70W WITH ISOLATED SHOWERS OCCURRING ELSEWHERE FROM 11N-32N BETWEEN 57W-73W. 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 1020 MB HIGH CENTERED NEAR 33N48W AND A 1026 MB HIGH CENTERED EAST OF THE AZORES NEAR 38N19W. EMBEDDED WITHIN THE SW PERIPHERY OF THIS SURFACE RIDGE...A WEAK 1010 MB SURFACE LOW IS CENTERED NEAR 17N51W AND CONTINUES TO MOVE WESTWARD. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING WITHIN 120 NM OF THE CENTER OF THE LOW. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ HUFFMAN