000 AXNT20 KNHC 181741 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST THU DEC 18 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 1645 UTC. ...THE ITCZ... ITCZ IS CENTERED ALONG 6N8W 5N17W 6N31W 6N46W 5N54W. SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 90 NM N OF THE AXIS FROM 11W-15W...WITHIN 75 NM S OF THE AXIS FROM 18W-20W...AND WITHIN 180 NM S OF THE AXIS FROM 45W-50W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM S OF THE AXIS E OF 17W TO INLAND OVER W AFRICA...WITHIN 90/120 NM N OF THE AXIS FROM 15W-18W...AND FROM 32W-39W. CLUSTERS OF SIMILAR CONVECTION DOT THE REMAINDER OF THE AREA FROM 2N-7N BETWEEN 21W-29W AND FROM 6N-11N BETWEEN 43W-52W. ...DISCUSSION... GULF OF MEXICO... A LARGE AMPLIFIED UPPER RIDGE COVERS THE GULF TO OVER THE SE US CENTERED OVER THE BAY OF CAMPECHE PROVIDING MAINLY LIGHT FLOW AND STABLE AIR ALOFT ACROSS THE ENTIRE GULF...EXCEPT FOR OVER FLORIDA WHERE UPPER LEVEL MOISTURE IS BEING DRIVEN S ON THE E PERIPHERY OF THE RIDGE. IN THE LOWER LEVELS...THE FRONT HAS DISSIPATED INLAND ALONG THE TEXAS COAST BUT STILL PROVIDING DENSE CLOUDS WITH SCATTERED SHOWERS INLAND FROM PENSACOLA FLORIDA TO NE MEXICO S OF MATAMOROS AND BROKEN TO OVERCAST CLOUDS WITH ISOLATED SHOWERS WITHIN 60 NM ALONG THE SAME COASTLINE. OTHERWISE...MAINLY FAIR CONDITIONS REMAINS ACROSS THE AREA WITH ONLY PATCHY LOW LEVEL CLOUDS WITH POSSIBLE ISOLATED SHOWERS BEING STEERED BY LIGHT/MODERATE FLOW AROUND A SURFACE RIDGE ANCHORED BY A 1026 MB HIGH OVER THE FLORIDA PANHANDLE NEAR TALLAHASSEE. LITTLE SIGNIFICANT CHANGE IS EXPECTED OVER THE NEXT COUPLE OF DAYS UNTIL THE NEXT COLD FRONT APPROACHES THE NW GULF LATE SAT/EARLY SUN. CARIBBEAN SEA... CONFLUENCE NEAR THE BASE OF AN UPPER TROUGH OVER THE W/CENTRAL ATLC IS ENHANCING SUBSIDENCE ACROSS THE ENTIRE AREA...LIMITING THE DEVELOPMENT OF ANY DEEP CONVECTION. HOWEVER...LOW LEVEL ISOLATED SHOWERS ARE FOUND ACROSS MUCH OF THE AREA GENERATED BY AN ELONGATED SURFACE TROUGH NE OF THE VIRGIN ISLANDS. RECENT SCATTEROMETER DATA INDICATED THAT THESE N TO NE WINDS ARE MAINLY IN THE 20-25 KT RANGE W OF 68W. SIMILAR WINDS/SHOWERS ARE EXPECTED THROUGH SAT BEFORE THE HIGH PRESSURE OVER THE W ATLC SHIFTS E ALLOWING THE FLOW TO WEAKEN. ATLANTIC OCEAN... DEEP LAYERED TROUGH IS OVER THE CENTRAL ATLC CONTINUING TO CAUSE SOME ACTIVE WEATHER TODAY...BUT LESS SO THAN YESTERDAY. A SURFACE TROUGH EXTENDS THROUGH A MID LEVEL LOW NEAR 33N57W INTO THE REGION NEAR ALONG 30N58W TO A WEAKENING 1011 MB NEAR 26N60W TO 21N64W. LOW LEVEL CONVERGENCE AND INSTABILITY NEAR THE LOW IS PRODUCING SCATTERED SHOWERS AND POSSIBLE ISOLATED THUNDERSTORMS WITHIN 60 NM OF LINE FROM 28N56W TO 23N62W. A LARGER AREA OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS IS TO THE SE OF THE LOW S OF 25N TO THE ITCZ FROM 43W-55W IN AN UPPER DIFFLUENT ZONE GENERATED BY THE WLY UPPER FLOW BEING AMPLIFIED TO THE E OF THE ABOVE SYSTEM AND POSSIBLY ENHANCED BY A WEAK SURFACE TROUGH ALONG 18N53W TO 14N55W. THE LOW IS EXPECTED BECOME GREATLY SHEARED AND SPLIT APART BY A SHORTWAVE TROUGH EARLY FRI. THE W ATLC IS RELATIVELY TRANQUIL BENEATH ABUNDANT DRY AIR ALOFT ON THE W SIDE OF THE UPPER LOW. HOWEVER...MODERATE/STRONG N/NE LOW LEVEL WINDS ARE STIRRING UP LOW LEVEL ISOLATED SHOWERS MAINLY E OF 74W. $$ WALLACE