000 AXNT20 KNHC 212350 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST FRI DEC 21 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... THE ITCZ IS PRETTY ACTIVE THIS EVENING. IT AXIS IS CENTERED ALONG 5N10W 5N20W 4N30W 3N40W AND INTO SOUTH AMERICA NEAR THE EQUATOR AT 50W. CLUSTERS OF MODERATE TO STRONG CONVECTION ARE FROM THE EQUATOR TO 6N BETWEEN 30W-40W...AND WITHIN 90 NM SOUTH OF AXIS BETWEEN 20W-29W. UPPER DIFFLUENCE IS ENHANCING CONVECTION ALONG THE ITCZ. DISCUSSION... GULF OF MEXICO... AS WAS PREDICTED BY THE COMPUTER MODELS...A SFC LOW DEVELOPED AND MOVED QUICKLY ACROSS THE NE QUADRANT OF THE GULF AND N FLORIDA 24 HOURS AGO...AND NOW IS CENTERED NEAR 31N79W. A COLD FRONT EXTENDS FROM THIS LOW ACROSS SOUTH FLORIDA AND THE GULF ALONG 25N85W 24N90W CURVING AS A STATIONARY FRONT INTO THE SW PORTION OF THE GULF. A RATHER SHARP WIND SHIFT IS ASSOCIATED WITH THE FRONT WITH SW WINDS OF 15 KT AHEAD OF THE FRONT AND NW TO N WINDS OF 10-15 KT W OF THE FRONT TO ABOUT 90W. THE FRONT IS FORECAST TO EXIT THE AREA TONIGHT AND A WEAK HIGH PRES WILL BUILD IN. A RETURN FLOW IS ALREADY ESTABLISHED OVER THE FAR W GULF IN ADVANCE OF A STRONGER COLD FRONT THAT WILL MOVE OFF THE TEXAS COAST SAT AFTERNOON. MODERATE TO STRONG NLY WINDS OF 25 TO 30 KT AND BUILDING SEAS CAN BE EXPECTED BEHIND FRONT. ALOFT...A RIDGE DOMINATES THE ENTIRE GULF WHILE A MID/UPPER LEVEL TROUGH IS LOCATED JUST EAST OF THE FLORIDA PENINSULA. THIS TROUGH SUPPORTS THE ABOVE MENTIONED LOW/FRONT. MODERATE TO STRONG SUBSIDENCE COVERS THE GULF EXCEPT THE NW CORNER WHERE A SUBTROPICAL JETSTREAM FROM THE EPAC IS ADVECTING ABUNDANT UPPER-LEVEL MOISTURE/HIGH CLOUDS. CARIBBEAN SEA... TRANQUIL WEATHER CONDITIONS PERSIST ACROSS MOST OF THE CARIBBEAN SEA THIS EVENING UNDER THE INFLUENCE OF A MID/UPPER-LEVEL RIDGE WHICH IS PRODUCING STRONG SUBSIDENCE AND A DRY/STABLE AIRMASS. A SFC TROUGH IS ALONG 63W SOUTH OF 16N GENERATING SOME SHOWER ACTIVITY OVER THE WINDWARD ISLANDS AND NE VENEZUELA. THE TRADE WINDS ARE ADVECTING SOME LOW LEVEL MOISTURE ACROSS NICARAGUA... COSTA RICA AND WESTERN PANAMA. A FEW PATCHES OF LOW LEVEL CLOUDS WITH ISOLATED SHOWERS ARE OVER THE REMAINDER OF THE BASIN. LIGHT TO MODERATE TRADES WILL PREVAIL OVER MUCH OF THE AREA THROUGH MONDAY. ATLANTIC OCEAN... MAIN FEATURE ACROSS THE FORECAST AREA IS THE 1006 MB LOW PRES LOCATED NEAR 31N79W WITH A COLD FRONT EXTENDING SW ACROSS THE NW BAHAMAS AND SOUTH FLORIDA INTO THE GULF OF MEXICO. MOST OF THE CONVECTIVE ACTIVITY ASSOCIATED WITH THIS SYSTEM IS WITHIN 140 NM AHEAD OF THE FRONT. LIGHTNING DATA REVEALS SCATTERED TSTMS EMBEDDED IN THIS AREA N OF 26N BETWEEN 70W-75W. A QUIKSCAT PASS FROM THIS MORNING SHOWED 20-30 KT WINDS NEAR THE LOW AND JUST N OF 31N W OF 70W WHERE GALE FORCE WINDS ARE OCCURRING. ACCORDING TO THE GFS COMPUTER MODEL...THE LOW WILL MOVE SE AND WEAKEN TONIGHT REACHING TO NEAR 29N70W BY SAT MORNING. A RIDGE WILL BUILD BEHIND THE LOW BETWEEN THE SE U.S. AND WEST-CENTRAL CUBA. THE TIGHT PRES GRADIENT BETWEEN THE LOW AND A HIGH SITUATED NORTH OF THE AREA WILL PRODUCE MODERATE TO STRONG NELY WINDS ACROSS THE W ATLC DURING THE UPCOMING WEEKEND. FARTHER EAST...A SFC TROUGH EXTENDS FROM A WEAK 1014 MB LOW LOCATED NEAR 34N46W TO 24N55W. SCATTERED SHOWERS AND TSTMS ARE WITHIN 125 NM AHEAD OF THE TROUGH N OF 25N. ANOTHER COLD FRONT ENTERS THE AREA NEAR 31N17W THEN CONTINUES SW AND W ALONG 27N25W TO 31N36W WHERE IT CONNECTS TO A WARM FRONT. A LARGE SFC RIDGE REMAINS FIXED OVER THE E ATLC TRANSPORTING FAIR WEATHER STRATOCUMULUS CLOUDS AROUND ITS PERIPHERY. IN THE TROPICAL ATLC...UPPER DIFFLUENCE IS SUPPORTING CONVECTION ALONG THE ITCZ. $$ GR