000 AXNT20 KNHC 251801 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU SEP 25 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 996 MB SURFACE LOW IS CENTERED NEAR 32N77W...OR ABOUT 170 NM SE OF THE SOUTH CAROLINA-NORTH CAROLINA BORDER. THIS LOW IS MOVING SLOWLY WESTWARD. THERE IS STILL A POSSIBILITY THAT THIS SYSTEM COULD DEVELOP INTO A SUBTROPICAL OR TROPICAL CYCLONE LATER TODAY. REGARDLESS OF WHETHER OR NOT THIS SYSTEM BECOMES A SUBTROPICAL OR TROPICAL CYCLONE...STRONG WINDS...COASTAL FLOODING...HIGH SURF...AND DANGEROUS RIP CURRENTS WILL CONTINUE ALONG PORTIONS OF THE U.S. EAST COAST DURING THE NEXT COUPLE OF DAYS. OUTER RAINBANDS AND GUSTY WINDS CONTINUE SPREADING ONSHORE FROM SOUTH CAROLINA TO VIRGINIA. A 1003 MB SURFACE LOW IS CENTERED NEAR 23N69W...OR ABOUT 150 NM NE OF THE TURKS AND CAICOS ISLANDS...MOVING NORTHWARD NEAR 10 KT. MODERATE WEST-SOUTHWESTERLY FLOW ALOFT HAS SHEARED CONVECTION AWAY FROM THE LOW LEVEL CIRCULATION...AND THIS SYSTEM IS NOT WELL ORGANIZED. CLUSTERS OF MODERATE CONVECTION ARE MAINLY OVER THE SOUTHWEST ATLANTIC WATERS FROM 20N-25N BETWEEN 62W-68W. UPPER-LEVEL WINDS COULD BRIEFLY BECOME MORE CONDUCIVE FOR DEVELOPMENT...AND THIS SYSTEM COULD BECOME A TROPICAL CYCLONE OVER THE NEXT DAY OR SO. ...TROPICAL WAVES... A NEW TROPICAL WAVE HAS BEEN ADDED TO THE 1200 UTC MAP ALONG 25W/26W S OF 17N MOVING W NEAR 15 KT. A LOOP OF MIMIC TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS DEPICTS A WELL-DEFINED MAXIMUM IN DEEP LAYER MOISTURE...WHICH HAD PREVIOUSLY PUSHED WEST OF THE AFRICAN COAST EARLY THIS WEEK. SCATTERED MODERATE CONVECTION IS OCCURRING 90 NM EITHER SIDE OF THE WAVE AXIS N OF 12N...AND VISIBLE SATELLITE IMAGERY DEPICTS LOW LEVEL CIRCULATION IN THE MOTION OF CLOUD ELEMENTS. A TROPICAL WAVE IS ALONG 36W/37W S OF 17N MOVING W 10-15 KT. THIS TROPICAL WAVE HAS BEEN RELOCATED EASTWARD FROM ITS 25/0600 UTC POSITION ALONG 42W/43W S OF 17N. SCATTERED MODERATE CONVECTION HAS BEEN NOTED FROM 11N-17N BETWEEN 33W-40W...WHERE TOTAL PRECIPITABLE WATER IS MAXIMIZED. VISIBLE SATELLITE IMAGERY NOW DEPICTS A WELL-DEFINED INVERTED-V SIGNATURE IN THE ASSOCIATED LOW LEVEL CLOUD ELEMENTS...AND COMPUTER MODEL GUIDANCE CONFIRMS THE PRESENCE OF LOW LEVEL CIRCULATION IN THE NEW LOCATION FOR THIS WAVE. ADDITIONALLY...EXTRAPOLATION BASED ON WAVE PASSAGE INFERRED FROM UPPER AIR TIME SECTION AT DAKAR SENEGAL SUPPORTS THIS NEW LOCATION. TROPICAL WAVE IS ALONG 68W S OF 15N MOVING W 10-15 KT. WAVE POSITION IS BASED ON CONTINUITY AS IT HAS ALMOST NO SATELLITE SIGNATURE AND NO ASSOCIATED SHOWERS/CONVECTION. TROPICAL WAVE IS ALONG 81W/82W S OF 16N MOVING W 10-15 KT. WAVE IS EMBEDDED WITHIN SOMEWHAT DRY STABLE AIR GENERALLY LIMITING CLOUD FORMATION AND SHOWERS...THOUGH ISOLATED SHOWERS ARE OCCURRING 90 NM EITHER SIDE OF THE WAVE AXIS S OF 10N IN THE PRESENCE OF AN UPPER TROUGH. TROPICAL WAVE IS ALONG 92W/93W S OF 20N MOVING W NEAR 10 KT. WAVE IS IN THE BAY OF CAMPECHE ACROSS S MEXICO INTO THE E PACIFIC REGION. ISOLATED SHOWERS ARE OCCURRING 90 NM EITHER SIDE OF THE WAVE AXIS IN THE BAY OF CAMPECHE AND OVER CENTRAL AMERICA....WITH ISOLATED SHOWER ACTIVITY FARTHER SOUTH INTO THE E PACIFIC. ...THE ITCZ... ITCZ AXIS IS ANALYZED ALONG 10N13W 8N24W 9N40W 9N54W 9N60W. CLUSTERS OF MODERATE WITH EMBEDDED ISOLATED STRONG CONVECTION ARE FROM 4N-12N BETWEEN 10W-21W...NEAR THE W AFRICAN COAST. ...DISCUSSION... GULF OF MEXICO... AN UPPER RIDGE AXIS EXTENDS EASTWARD FROM AN UPPER HIGH OVER THE W MEXICAN COAST ACROSS THE S GULF. AS A DEEP UPPER TROUGH OVER THE E CONUS AND W ATLANTIC ATTEMPTS TO DIG SOUTHWARD...THE WESTERLY UPPER FLOW OVER MUCH OF THE GULF CONTINUES TO STRENGTHEN. UNUSUALLY DRY AIR IN THE TROUGH CONTINUES TO PERCOLATE INTO THE NORTHERN AND CENTRAL GULF ON NORTHEASTERLY SURFACE WINDS... AFFECTING ADJACENT COASTAL REGIONS AS WELL. HOWEVER...UPPER LEVEL DIFFLUENT FLOW SOUTH OF THE UPPER RIDGE AXIS...COMBINED WITH LOW LEVEL CONVERGENCE IN THE VICINITY OF A SURFACE TROUGH EXTENDING ALONG THE EASTERN MEXICAN COAST...IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 18N-23N BETWEEN 89W-97W... AFFECTING WESTERN AREAS OF THE BAY OF CAMPECHE AND THE YUCATAN PENINSULA. CARIBBEAN SEA... THE UPPER RIDGE OVER THE GULF EXTENDS EASTWARD INTO THE NW CARIBBEAN N OF 13N AND W OF 80W. THE PERSISTENT SHARP UPPER TROUGH OVER THE CENTRAL CARIBBEAN IS BECOMING COUPLED WITH THE DEEP UPPER TROUGH OVER THE W ATLANTIC AND NORTHERN GULF. AS A RESULT...DEEP LAYER DRY AIR FROM THE TROUGH FURTHER NORTH IS BEING TRANSPORTED SOUTHWARD INTO THE CENTRAL CARIBBEAN. THIS DRY AIR IS RESULTING IN FAIR WEATHER CONDITIONS ACROSS MUCH OF THE GULF. TO THE EAST OF THIS SHARP UPPER TROUGH IS ANOTHER UPPER RIDGE THAT IS ANCHORED BY AN UPPER HIGH OVER THE LESSER ANTILLES NEAR 15N61W. WEAK FLOW ALOFT FOR THE MOST PART IS PREVENTING THE DEVELOPMENT OF ANY SUBSTANTIAL CONVECTION ACROSS THE CARIBBEAN. ATLANTIC OCEAN... TWO MAIN CONCERNS FOR THE W ATLC ARE THE ACTIVITY DESCRIBED IN THE SPECIAL FEATURES SECTION ABOVE. THE DEEP UPPER TROUGH ASSOCIATED WITH THE FIRST SPECIAL FEATURE COVERS THE W ATLC W OF 70W AND EXTENDS INTO THE CENTRAL CARIBBEAN. STRONG VERTICAL SUPPORT E OF THE TROUGH AXIS IS INTENSIFYING A 996 MB LOW NEAR 32N77W. IN THE SW ATLANTIC...DRIER AND SLIGHTLY COOLER AIR IS WRAPPING AROUND THIS LOW BEHIND A COLD FRONT THAT EXTENDS FROM 32N72W TO NEAR 29N73W. FROM THIS POINT...A STATIONARY FRONT EXTENDS TO THE SW TO NEAR 26N76W TO 24N80W. A WEAK SURFACE TROUGH BEHIND THESE FRONTS ALSO TRAILS SOUTHWESTWARD FROM THE LOW TO NEAR 28N76W AND TO NEAR 26N80W. WHILE THERE IS SOME SURFACE CONVERGENCE IN THE VICINITY OF THESE FEATURES...DEEP LAYER DRY AIR IN THE BASE OF THE UPPER TROUGH IS INHIBITING CONVECTIVE DEVELOPMENT ACROSS THE SW ATLANTIC. TO THE WEST OF THE SURFACE TROUGH...NORTHWESTERLY SURFACE WINDS OF 20-25 KT ARE OCCURRING. THE SECOND SURFACE LOW DISCUSSED IN THE SPECIAL FEATURES SECTION IS GENERATING GALE FORCE WINDS OVER PORTIONS OF THE SW N ATLC...AND A GALE WARNING IS IN EFFECT FROM 21N-29N BETWEEN 65W-69W. THIS SURFACE LOW IS BENEATH AN UPPER RIDGE...WITH DIFFLUENCE IN THE UPPER FLOW ENHANCING THE ASSOCIATED CONVECTION DISCUSSED IN THE SPECIAL FEATURES SECTION. THIS UPPER RIDGE COVERS MUCH OF THE W ATLC...AND IS ANCHORED BY THE UPPER HIGH NEAR 15N61W. AN UPPER LEVEL CLOSED LOW NEAR 25N46W CONTINUES TO WEAKEN AND IS BECOMING AN OPEN UPPER TROUGH...WITH AN ATTENDANT 1013 MB SURFACE LOW NEAR 30N25W AND A SURFACE TROUGH TRAILING SOUTHWARD FROM THE SURFACE LOW TO NEAR 25N25W. ISOLATED SHOWERS ARE OCCURRING FROM 22N-26N BETWEEN 46W-50W. DEEP LOW PRESSURE IS AFFECTING THE NE ATLC CENTERED NEAR 31N22W...WITH ISOLATED SHOWERS FROM 29N-32N BETWEEN 20W-25W. THE TYPICAL E/W UPPER RIDGE THAT EXTENDS FROM AFRICA TO NEAR 45W ALONG 13N CONTINUES TO BE SUPPRESSED TO THE S DUE TO THE UPPER TROUGHS MENTIONED ABOVE. A WEAK SURFACE RIDGE REMAINS OVER THE CENTRAL ATLC N OF 23N BETWEEN 30W-50W WITH A 1021 MB HIGH NEAR 30N38W. THESE RIDGES AND SURFACE HIGH ARE RESULTING IN GENERALLY FAIR WEATHER ACROSS THE REMAINDER OF THE ATLC. $$ COHEN/HUFFMAN/KIMBERLAIN