000 AXNT20 KNHC 202343 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST THU DEC 20 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 6N10W 4N25W 5N35W 4N45W AND INTO SOUTH AMERICA NEAR 2N52W. CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION ARE WITHIN 180 NM EITHER SIDE WEST OF 27W. SIMILAR CONVECTION IS NEAR 6N14W AND INLAND OVER LIBERIA. A DIFFLUENT PATTERN ALOFT IS ENHANCING THIS CONVECTIVE ACTIVITY. DISCUSSION... GULF OF MEXICO... A COLD FRONT HAS ENTERED THE NW CORNER OF THE GULF. AS OF 2100 UTC THE FRONTAL SYSTEM EXTENDS FROM CENTRAL LOUISIANA TO NE MEXICO NEAR 25N98W. AN AREA OF SHOWERS AND TSTMS IS AHEAD OF THE FRONT AFFECTING THE N-CENTRAL GULF WATERS...PARTICULARLY N OF 27N BETWEEN 87W AND 93W. THIS CONVECTIVE ACTIVITY IS ALSO AFFECTING THE FLORIDA PANHANDLE AND PARTS OF ALABAMA AND MISSISSIPPI. MODERATE TO STRONG S TO SW WINDS ARE BLOWING AHEAD OF THE FRONT. AN EARLIER ASCAT PASS REVELED 20 TO 25 KT MAINLY OVER THE MIDDLE GULF N OF 26N. THIS WINDS WILL GRADUALLY SPREAD EWD OVER THE NE QUADRANT OF THE GULF LATE TONIGHT AS LOW PRES FORMS OVER SE LOUISIANA AND QUICKLY SLIDES E TO ACROSS N FLORIDA THROUGH FRI. WINDS WILL SHIFT TO THE NW IN THE WAKE OF THE FRONT. A RIDGE OF HIGH PRESSURE CONTINUES TO DOMINATE THE REMAINDER OF THE GULF. ALOFT...A SHORT-WAVE TROUGH MOVING EWD ACROSS THE LOWER MISSISSIPPI VALLEY SUPPORTS THE COLD FRONT. A SUBTROPICAL JET WITH CORE WINDS OF NEAR 110 KT IS CENTERED OVER THE N GULF WATERS/N FLORIDA DRAWING UPPER-LEVEL MOISTURE ACROSS THE GULF FROM THE E PACIFIC. NEAR ZONAL FLOW SOUTH OF THE JET CONTINUES TO MAINTAIN DRY AND STABLE CONDITIONS. THE NEXT COLD FRONT IS EXPECTED TO MOVE INTO THE NW GULF SAT AFTERNOON... AND EXTEND FROM THE WRN FLORIDA TO E BAY OF CAMPECHE BY SUN AFTERNOON. MODERATE TO STRONG NLY WINDS AND BUILDING SEAS CAN BE EXPECTED BEHIND FRONT. CARIBBEAN SEA... WEATHER CONDITIONS ACROSS THE CARIBBEAN SEA ARE PRETTY QUIET THIS EVENING UNDER THE INFLUENCE OF A MID/UPPER-LEVEL RIDGE WHICH IS PRODUCING STRONG SUBSIDENCE AND IMPLIED DRY/STABLE AIRMASS. THE SURFACE TROUGH THAT WAS AFFECTING THE NW CARIBBEAN DURING THE PREVIOUS DAYS HAS WEAKENED. ONLY A FEW PATCHES OF LOW LEVEL CLOUDS WITH ISOLATED SHOWERS REMAINS OVER THE AREA. TYPICAL FRAGMENTS OF MOISTURE ARE BRINGING ISOLATED PASSING SHOWERS TO THE NE CARIBBEAN... INCLUDING PUERTO RICO AND THE SURROUNDING ISLANDS...AND TO THE ABC ISLANDS. ADDITIONAL POCKETS OF MOISTURE ARE ALSO STREAMING ACROSS NICARAGUA AND COSTA RICA UNDER A NELY WIND FLOW. LIGHT TO MODERATE TRADES WILL PREVAIL OVER MUCH OF THE AREA THROUGH MONDAY. ATLANTIC OCEAN... A WEAK PRES GRADIENT CHARACTERIZED BY A COLD FRONT CLIPPING THE REGION ALONG 31N AND A WEAK SFC TROUGH ALONG 66W/67W DOMINATES THE W ATLC. A STATIONARY FRONT EXTENDS FROM 28N59W TO 31N40W THEN CONTINUES NE AS A COLD FRONT CROSSING E OF THE AZORES. A LOW IS EXPECTED TO DEVELOP ALONG THIS FRONTAL BOUNDARY NEAR 28N56W DURING THE NEXT 24 HOURS OR SO. SATELLITE IMAGERY SHOWS ALREADY A LARGE AREA OF SHOWERS WITH ISOLATED TSTMS NEAR THE TAIL END OF THE STATIONARY FRONT. FAIR WEATHER STRATOCUMULUS CLOUDS ARE BEING TRANSPORTED AROUND A 1022 MB SFC HIGH CENTERED NEAR 28N39W. A FRONTAL BOUNDARY ASSOCIATED WITH A DEEP-LAYERED TROUGH OVER THE E ATLC TRAILS ACROSS THE AFRICAN COAST AND EXTENDS TO 22N16W. A NARROW BAND OF MAINLY LOW CLOUDS IS RELATED TO THE FRONT. IN THE TROPICAL ATLC...DIFFLUENCE ASSOCIATED WITH AN UPPER-LEVEL HIGH LOCATED OVER NE BRAZIL IS SUPPORTING CONVECTION ALONG THE ITCZ AND NEAR ZONAL FLOW CONTINUES TO TRANSPORT UPPER-LEVEL MOISTURE EASTWARD ACROSS THE REGION S OF 14N. A SFC TROUGH WAS ANALYZED ON THE 1800 UTC MAP ALONG 59W SOUTH OF 14N. AN ASCAT PASS FROM THIS MORNING SHOWED SOME WIND SHIFT ASSOCIATED WITH THIS TROUGH. THERE IS ALSO SCATTERED MODERATE CONVECTION IS THIS AREA ENHANCED BY UPPER DIFFLUENCE. THIS SHOWER ACTIVITY IS AFFECTING THE WINDWARD ISLANDS AND NE VENEZUELA. $$ GR