000 AXNT20 KNHC 291046 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT MON SEP 20 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1000 UTC. ...SPECIAL FEATURES... THE LOW PRESSURE SYSTEM IN THE NORTH CENTRAL ATLANTIC HAS BECOME BETTER ORGANIZED AND HAS GAINED TROPICAL CHARACTERISTICS. AT 0600 UTC...THE LOW WAS UPGRADED TO SUBTROPICAL STORM LAURA. AS OF 0900 UTC...THE CENTER OF SUBTROPICAL STORM LAURA IS LOCATED NEAR 37.2N47.3W AND IS MOVING TOWARD THE WNW AT 7 KT. ESTIMATED CENTRAL PRESSURE IS 993 MB AND MAXIMUM SUSTAINED WINDS ARE 50 KT WITH HIGHER GUSTS. LAURA IS EXPECTED TO GRADUALLY TURN TOWARD THE NORTHWEST AND THEN TOWARD THE NORTH WITH AN INCREASE IN FORWARD SPEED BY TUESDAY. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 300 NM. FOR SPECIFIC INFORMATION ON SUBTROPICAL STORM LAURA PLEASE READ THE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT2/WTNT32 KNHC AND THE FULL FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 25W SOUTH OF 17N. THE WAVE IS MOVING WESTWARD NEAR 10 KT. THE SSMI-DERIVED TPW INDICATES A MOISTURE MAXIMUM JUST OVER THE CAPE VERDE ISLANDS. THE FIRST FEW VISIBLE SATELLITE IMAGES OF THE DAY REVEAL AFRICAN DUST BEHIND THE WAVE AXIS NORTH OF 14N AS WELL AS BROAD CYCLONIC TURNING NEAR 10N. SCATTERED SHOWERS ARE WITHIN 150 NM W OF THE AXIS BETWEEN 12N-15N. CLUSTERS OF MODERATE CONVECTION ARE ALSO WITHIN 160 NM WEST AND 60 NM EAST OF THE AXIS FROM 6N-10N. A TROPICAL WAVE IS ALONG 42W SOUTH OF 19N MOVING WEST 10 TO 15 KT. BROAD LOW LEVEL CIRCULATION IS VISIBLE ON SATELLITE IMAGERY NORTH OF 14N. A CLUSTER OF MODERATE CONVECTION IS BETWEEN 39W AND THE AXIS FROM 6N-10N. A TROPICAL WAVE IS ALONG 54W SOUTH OF 16N MOVING WEST NEAR 10 KT. AN UPPER-LEVEL LOW CENTERED EAST OF THE LESSER ANTILLES IS PRODUCING MODERATE TO STRONG UPPER-LEVEL SWLY FLOW OVER THE WAVE. STRONG SUBSIDENCE ALOFT IN PREVENTING SIGNIFICANT CONVECTION FROM DEVELOPING IN THE VICINITY OF THE WAVE. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 9N13W 10N24W 7N31W 10N43W AND INTO SOUTH AMERICA NEAR 8N60W. IN ADDITION TO CONVECTION ASSOCIATED WITH TROPICAL WAVES...CLUSTERS OF MODERATE CONVECTION ARE BETWEEN 18W AND THE WEST COAST OF AFRICA FROM 5N TO 11N. A CLUSTER OF MODERATE TO STRONG CONVECTION IS FROM 13N-15N BETWEEN 20W-23W. SCATTERED MODERATE CONVECTION IS WITHIN 130 NM S OF THE AXIS BETWEEN 33W-38W. ...DISCUSSION... THE GULF OF MEXICO... A BROAD LOW PRESSURE SYSTEM IS MOVING INTO THE SOUTH-CENTRAL GULF FROM THE YUCATAN PENINSULA. AS OF 0900 UTC THE 1010 MB LOW CENTER WAS ANALYZED NEAR 22N89W. A SFC TROUGH EXTENDS FROM THE LOW CENTER ALONG 24N88W 26N85W TO NEAR TAMPA BAY. NUMEROUS SHOWERS AND THUNDERSTORMS ARE OVER THE SE GULF WITHIN 150 NM OF THE TROUGH. THE LOW IS FORECAST TO MOVE RAPIDLY NE...REACHING THE FLORIDA PENINSULA NEAR TAMPA BAY EARLY TUE. E TO SE WINDS 10-15 KT ARE OBSERVED IN THIS REGION. A STRONG PRESSURE GRADIENT BETWEEN THIS LOW PRESSURE AREA AND HIGHER PRESSURE OVER THE WESTERN GULF IS PRODUCING NLY WINDS 15-20 KT OVER THE SW PORTION OF THE GULF INCLUDING THE BAY OF CAMPECHE. NE WINDS 10-15 KT COVER THE REMAINDER OF THE GULF. ALOFT...A MID/UPPER LEVEL TROUGH IS MOVING OVER THE WESTERN ATLC WITH ITS AXIS ALONG 93W. UPPER-LEVEL SWLY WINDS AHEAD OF THIS TROUGH ARE TRANSPORTING ABUNDANT UPPER LEVEL MOISTURE ACROSS THE SE GULF...AS WELL AS LIMITING DEVELOPMENT OF THE AFOREMENTIONED SFC LOW. THE CARIBBEAN SEA... UPPER LEVEL DIVERGENT FLOW BETWEEN THE TROUGH OVER THE WESTERN GULF OF MEXICO AND A HIGH PRESSURE RIDGE OVER THE W ATLC IS GENERATING WIDELY SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE CENTRAL AND WESTERN CARIBBEAN W OF 74W. THE EASTERN CARIBBEAN REMAINS UNDER MOSTLY CLEAR CONDITIONS DUE TO A DRY AND STABLE AIRMASS ALOFT. MODERATE TRADE WINDS PERSIST THROUGHOUT THE CARIBBEAN. THE ATLANTIC OCEAN... SUBTROPICAL STORM LAURA HAS FORMED IN THE NORTH-CENTRAL ATLANTIC. SEE SPECIAL FEATURES SECTION ABOVE FOR MORE DETAILED INFORMATION. CONVECTION IN THE FAR WESTERN ATLC OFF THE COAST OF FLORIDA HAS DECREASED OVER THE LAST FEW HOURS...HOWEVER ABUNDANT UPPER LEVEL MOISTURE CONTINUES TO STREAM ACROSS FLORIDA OVER THE ATLC WATERS DUE TO STRONG SWLY FLOW AHEAD OF AN UPPER TROUGH OVER THE GULF OF MEXICO. PATCHY CLOUDS WITH POSSIBLE EMBEDDED SHOWERS ASSOCIATED WITH SUBTROPICAL STORM LAURA EXTEND SOUTHWARD TO 25N BETWEEN 35W-55W. THE EASTERN ATLANTIC IS DOMINATED BY A HIGH PRESSURE RIDGE EXTENDING SOUTHWARD FROM THE AZORES. ALOFT...A RIDGE/TROUGH/RIDGE PATTERN REMAINS SITUATED ACROSS THE ATLANTIC. THE WESTERN RIDGE IS CENTERED ON AN UPPER HIGH LOCATED NE OF THE BAHAMAS NEAR 27N71W. A TROUGH CONNECTS AN UPPER LOW NEAR 32N43W TO A SECOND UPPER LOW EAST OF THE ANTILLES CENTERED NEAR 16N57W. THE EASTERN-MOST RIDGE IS CENTERED ON AN UPPER HIGH NEAR 18N24W. FLOW AROUND THIS RIDGE CONTINUES TO ENHANCE CONVECTION ALONG THE ITCZ EAST OF 44W. $$ WADDINGTON