000 AXNT20 KNHC 111800 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT MON AUG 11 2008 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 LOCATED OVER THE CENTRAL ATLANTIC ALONG 47W/48 OR ABOUT 720 NM EAST OF THE WINDWARD ISLANDS IS SUPPORTING AN AREA OF DISORGANIZED SCATTERED SHOWERS AND THUNDERSTORMS FROM 12N-15N BETWEEN 47W-51W. A BROAD AREA OF LOW PRES IS ASSOCIATED WITH THIS WAVE CENTERED NEAR 12N47W. ALTHOUGH ASSOCIATED SHOWER AND THUNDERSTORM ACTIVITY REMAINS LIMITED AT THIS TIME...ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR GRADUAL DEVELOPMENT...AND THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION DURING THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD AT 15 TO 20 MPH. A 1011 MB BROAD LOW PRES AREA IS LOCATED OVER THE EASTERN ATLANTIC NEAR 11N29W. VIS SAT IMAGERY SHOWS SOME SIGNS OF BANDING...INDICATING THAT THE SYSTEM HAS BECOME A LITTLE BETTER ORGANIZED TODAY. A LARGE AREA OF SHOWERS AND THUNDERSTORMS ACCOMPANIES THIS LOW...AND A TROPICAL DEPRESSION COULD FORM DURING THE NEXT DAY OR TWO AS IT MOVES WESTWARD AT ABOUT 10 MPH. ...TROPICAL WAVES... A TROPICAL WAVE IS APPROACHING THE CAPE VERDE ISLANDS. ITS AXIS IS ALONG 22W/23W S OF 17N MOVING W AT 10-15 KT. SOME CYCLONIC TURNING IS SEEN ALONG THE WAVE AXIS NEAR 13N. SCATTERED MODERATE CONVECTION IS NOTED MAINLY AHEAD OF THE WAVE LINE FROM 11N-14N BETWEEN 23W-26W. SIMILAR CONVECTION IS WITHIN 60 NM BEHIND THE WAVE APEX FROM 13N-14N. A TROPICAL WAVE IS ALONG 70W S OF 20N MOVING W 15-20 KT. A WEAK INVERTED-V PATTERN IS SEEN ON VIS SAT IMAGERY. THE MIMIC-TPW INDICATES THAT MOISTURE ASSOCIATED WITH THIS FEATURE HAS SPLIT IN TWO PIECES. ONE REMAINS OVER THE CARIBBEAN SEA SOUTH OF HISPANIOLA WHILE THE SECOND ONE IS MOVING NWD OVER THE W ATLC. A SURGE OF AFRICAN DUST CONTINUES TO FOLLOWS THIS WAVE AS SEEN ON VIS SAT IMAGERY AND THE SAHARAN AIR LAYER FROM CIMSS. AN ACTIVE TROPICAL WAVE EXTENDS FROM THE CAYMAN ISLANDS TO PANAMA ALONG 80W. A LARGE AREA OF MODERATE TO ISOLATED STRONG CONVECTION IS RELATED TO THE WAVE AND COVERS THE SW CARIBBEAN S OF 15N W OF 75W. MOISTURE ASSOCIATED WITH THIS TROPICAL WAVE WILL GRADUALLY SPREAD OVER CENTRAL AMERICA LATE TODAY THROUGH WED INCREASING THE CHANCE OF RAIN PARTICULARLY IN NICARAGUA AND HONDURAS. A DIFFLUENT PATTERN ALOFT IS HELPING TO INDUCE THIS CONVECTIVE ACTIVITY. ...THE ITCZ... THE ITCZ IS CENTERED ALONG 12N17W 12N25W 10N34W 13N45W 7N58W. OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE TWO TROPICAL WAVES AND THE LOW NEAR 11N29W...ISOLATED MODERATE CONVECTION IS FROM 8N-12N E OF 21W TO THE AFRICAN COAST...AND FROM 6N-10N BETWEEN 34W-40W. ...DISCUSSION... GULF OF MEXICO... AN UPPER-LEVEL HIGH CENTERED OVER THE BIG BEND REGION OF TEXAS EXTENDS RIDGING OVER THE GULF WATERS NORTH OF 20N. AN UPPER LEVEL TROUGH LIES SOUTH OF THE RIDGE AND EXTENDS FROM THE W ATLC THROUGH THE STRAITS OF FLORIDA AND YUCATAN CHANNEL ALONG 19N TO THE MEXICO COASTLINE NEAR 19N96W. UPPER DIFFLUENCE BETWEEN THE RIDGE AND AN UPPER LOW OVER THE CARIBBEAN SEA IS ENHANCING SCATTERED SHOWERS AND TSTMS OVER SOUTH FLORIDA...THE KEYS AND THE E PORTION OF THE GULF. MOSAIC DOPPLER RADAR FROM THE SE U.S. ALSO SHOWS SCATTERED SHOWERS AND TSTMS OVER THE N GULF WATERS N OF 28N BETWEEN 85W-90W INCLUDING THE FLORIDA PANHANDLE AND PARTS OF SE LOUISIANA. THIS CONVECTIVE ACTIVITY IS RELATED TO A DISSIPATING FRONTAL BOUNDARY. AT THE SURFACE...A RIDGE ANCHORED ON A 1017 MB HIGH OVER THE SE GULF NEAR 25N85W AT 1500 UTC DOMINATES THE REMAINDER OF THE GULF. THE SURFACE CIRCULATION AROUND THIS HIGH IS PROVIDING THE WRN AND CENTRAL GULF WITH LIGHT TO MODERATE SOUTHERLY RETURN FLOW. THESE WINDS ARE EXPECTED TO GRADUALLY INCREASE THROUGH TUE AS A LOW PRESSURE SYSTEM DEVELOPS OVER TEXAS AND NE MEXICO. CARIBBEAN SEA... AN UPPER-LEVEL LOW IS CENTERED BETWEEN THE CAYMAN ISLANDS AND JAMAICA WITH A TROUGH EXTENDING EWD ACROSS HISPANIOLA INTO THE CENTRAL ATLC TO ANOTHER UPPER-LEVEL LOW LOCATED NEAR 27N51W. SOUTH OF THIS UPPER LOW THERE IS AN UPPER-LEVEL HIGH SITUATED OVER THE SW CARIBBEAN WITH THE RIDGE AXIS EXTENDING TO THE E OVER NORTHERN SOUTH AMERICA...AND TO THE W OVER CENTRAL AMERICA. THIS SYSTEM IS ENHANCING CONVECTION OVER THE SW CARIBBEAN. MODERATE TO STRONG SUBSIDENCE AND DRY AIR IS OVER THE ERN CARIBBEAN WITH PATCHES OF SHALLOW MOISTURE CROSSING THE WINDWARD ISLANDS. MODERATE TO STRONG EASTERLY TRADE WINDS ARE BLOWING ACROSS THE BASIN WITH THE STRONGEST WINDS OFFSHORE OF THE NRN COLOMBIAN COAST. TWO TROPICAL WAVES ARE MOVING WWD ACROSS THE BASIN...SEE TROPICAL WAVE SECTION FOR MORE DETAILS. ATLANTIC OCEAN... AN UPPER LEVEL TROUGH IS LOCATED OVER THE ERN U.S. INTO THE FAR W ATLC WITH THE ASSOCIATED FRONTAL BOUNDARY OVER THE CAROLINAS AND THE SE U.S.. AN UPPER-LEVEL RIDGE IS TO THE SE CENTERED NEAR 27N69. UPPER DIFFLUENCE BETWEEN THIS HIGH AND THE UPPER-LEVEL LOW SPINNING BETWEEN THE CAYMAN ISLANDS AND JAMAICA IS PRODUCING A 140 NM BAND OF SHOWERS AND TSTMS FROM THE NW BAHAMAS ALL THE WAY NE TO BEYOND 31N70W. THIS ACTIVITY IS ALSO ASSOCIATED WITH THE REMNANTS OF A FRONTAL BOUNDARY. ELSEWHERE AN UPPER LOW IS OVER THE CENTRAL ATLC NEAR 27N51W WITH ANOTHER WEAK UPPER-LEVEL LOW OVER THE ERN ATLC NEAR 29N28W. AN UPPER-LEVEL HIGH IS LOCATED NEAR 22N19W...AND A SECOND ONE IS NEAR 17N42W WITH THE RIDGE COVERING THE DEEP TROPICS. THESE UPPER SYSTEMS ARE ENHANCING CONVECTION ALONG THE ITCZ. OTHERWISE...THE ATLANTIC FORECAST AREA IS DOMINATED BY A 1025 MB SURFACE HIGH CENTERED NEAR 34N46W. THIS HIGH EXTENDS A RIDGE SW INTO THE E GULF AND IS FORECAST TO MOVE NEWD DURING THE NEXT 24 HOURS OR SO. $$ GR