000 AXNT20 KNHC 061801 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST THU DEC 06 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND THE 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 ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 6N10W 5N30W 6N41W 2N51W. SCATTERED MODERATE CONVECTION IS WITHIN 200 NM NORTH OF THE AXIS BETWEEN 32W-40W. WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 150 NM SOUTH OF AXIS EAST OF 20W TO THE AFRICAN COAST. 34W-42W. DISCUSSION... THE GULF OF MEXICO... AS OF 1500 UTC...A FRONTAL SYSTEM EXTENDS EAST TO WEST ACROSS THE NORTHERN GULF WATERS FROM JUST N OF TAMPA BAY TO THE DEEP SOUTH IN TEXAS. THIS FRONT IS VERY DRY WITH LITTLE CLOUDS SEEN ON SATELLITE PHOTOS NEAR THE BOUNDARY. HOWEVER...THERE IS SOME CLOUDINESS ALONG THE MEXICAN COAST AND ALSO IN THE SE GULF NEAR THE TAIL END OF A PREFRONTAL TROUGH. MOSAIC DOPPLER RADAR FROM THE SE U.S. REVEALS A BAND OF SCATTERED SHOWERS AND TSTMS IN THE STRAITS OF FLORIDA PUSHING TOWARD THE NW BAHAMAS. ISOLATED SHOWERS ARE OVER PORTIONS OF S FLORIDA. A VERY WEAK SFC PRES PATTERN REMAINS AHEAD OF THE FRONT RESULTING IN MAINLY LIGHT AND VARIABLE WINDS ACROSS THE AREA. NLY WINDS OF 10 TO 15 KT ARE FOUND BEHIND THE FRONT...PARTICULARLY OVER THE NE CORNER OF THE GULF. THIS FRONT IS FORECAST TO MOVE NORTH OF THE AREA AS A WARM FRONT TONIGHT. CURRENTLY...THE WEST PORTION OF THE FRONT HAS BECOME NEARLY STATIONARY. IN THE MID AND UPPER LEVELS...A WELL DEFINED CUT-OFF LOW IS SPINNING OVER NE MEXICO. UPPER-LEVEL SWLY WINDS TO THE E OF THE LOW ARE ADVECTING ABUNDANT MID/UPPER LEVEL MOISTURE ACROSS MOST OF THE GULF. THE CARIBBEAN SEA... WEATHER CONDITIONS REMAIN PRETTY QUIET ACROSS THE BASIN THIS AFTERNOON. VIS SAT IMAGERY SHOWS TYPICAL POCKETS OF LOW LEVEL MOISTURE MOVING WWD UNDER AN ELY WIND FLOW. A WEAK SFC TROUGH IS ANALYZED ACROSS THE MONA PASSAGE BASED ON SFC OBSERVATIONS AND SATELLITE PICTURES. SCATTERED SHOWERS ARE FOUND ON THE NORTHERN END OF THE TROUGH NEAR 21N66W. THE SAN JUAN DOPPLER RADAR DEPICTS SCATTERED SHOWERS AND A FEW THUNDERSTORMS IN ASSOCIATION WITH THIS TROUGH...WHICH IS EXPECTED TO MOVE WEST AND AWAY FROM PUERTO RICO THIS AFTERNOON. THIS TROUGH WILL PROBABLY ENHANCE THE SHOWER ACTIVITY OVER HISPANIOLA THIS AFTERNOON. LIKE THE GULF OF MEXICO...WEAK SFC PRES PATTERN INDUCED BY THE SERIES OF WEAK FRONTAL TROUGHS N OF THE AREA IS ALLOWING ELY TRADES TO BE LIGHT ACROSS THE BASIN. ALOFT...A BROAD RIDGE COVERS THE CARIBBEAN SEA ANCHORED ON A HIGH OVER NW VENEZUELA. SLY WINDS ON THE WESTERN SIDE OF THE RIDGE ARE TRANSPORTING MID/UPPER-LEVEL MOISTURE/HIGH CLOUDS FROM THE EPAC INTO THE SW CARIBBEAN THROUGH CENTRAL AMERICA. THE RELAXED TRADE WIND FLOW IS NOT EXPECTED TO LAST MUCH LONGER AS STRONG RIDGING BUILDS NE OF THE AREA. WINDS ARE EXPECTED TO INCREASE TONIGHT. THE ATLANTIC OCEAN... A RATHER QUICK MOVING COLD FRONT HAS PUSHED OFF THE E COAST OF THE U.S. EXTENDING FROM 31N70W THROUGH N-CENTRAL FLORIDA. THIS FRONT IS FAIRLY WEAK AND DRY IN NATURE. A PREFRONTAL TROUGH... POSSIBLY ASSOCIATED WITH AN OLD FRONTAL BOUNDARY RUNS FROM 27N76W ACROSS THE STRAITS OF FLORIDA TO 23N86W. LOW-LEVEL CONVERGENCE ALONG THIS BOUNDARY IS PRODUCING SCATTERED SHOWERS AND TSTMS ACROSS THE NW BAHAMAS...THE STRAITS OF FLORIDA AND THE FLORIDA KEYS AND COASTAL WATERS. A SFC TROUGH EXTENDS FROM 29N50W TO 20N54W. THE WIND SHIFT ASSOCIATED WITH THIS TROUGH IS WELL DEFINED ON AN EARLIER QUIKSCAT PASS. VIS SAT IMAGERY IS STILL SHOWING A SWIRL OF LOW CLOUDS SPINNING OVER THE CENTRAL ATLC NEAR 22N57W...MOVING WWD AHEAD OF THE ABOVE MENTIONED TROUGH. ANOTHER SFC TROUGH IS OVER THE TROPICAL ATLC EXTENDING FROM 21N42W TO 9N39W. SCATTERED MODERATE CONVECTION IS SEEN JUST BEHIND THE TROUGH BETWEEN THE ITCZ AXIS AND 14N. SOME CYCLONIC TURNING IS ALONG THE TROUGH AXIS NEAR 17N. A STRONG SFC RIDGE DOMINATES THE EASTERN ATLC CENTERED ON A 1037 MB HIGH NEAR THE AZORES. A DIFFERENCE IN PRES BETWEEN THIS HIGH AND THE TROUGH OVER THE TROPICAL ATLC IS PRODUCING A LARGE AREA OF STRONG ELY TRADES BETWEEN THE TROUGH AXIS AND THE WEST COAST OF AFRICA. THE MID AND UPPER PATTERN IS QUITE AMPLIFIED CONSISTING OF A LARGE ANTICYCLONE OVER THE AZORES AND A BROAD ELONGATED TROUGH TRAPPED S OF THE HIGH. THE BROAD TROUGH HAS AN EMBEDDED UPPER LOW JUST SW OF THE CAPE VERDE ISLANDS NEAR 24N24W. A JET STREAM BRANCH IS ON THE S SIDE OF THE TROUGH. WV IMAGERY SHOWS A BAND OF TRANSVERSE HIGH CLOUDS RELATED TO THIS FEATURE. UPPER DIFFLUENCE BETWEEN THE UPPER LEVEL TROUGH AND AN UPPER HIGH LOCATED NEAR 5N45W IS HELPING TO INDUCE CONVECTION N OF THE ITCZ AND BEHIND THE TROPICAL ATLC TROUGH. THE REMAINDER OF THE FORECAST AREA... WEST OF 50W IS QUIET UNDER A FAIRLY UNIFORM ZONAL UPPER FLOW. $$ GR