000 AXNT20 KNHC 310005 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 705 PM EST SUN DEC 30 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 ...SPECIAL FEATURE... A GALE-FORCE 1008 MB CYCLONE IS PRESENT AT 27N35W OR ABOUT 750 NM SSW OF THE AZORES. THE SYSTEM HAS LOST SOME OF ITS CONVECTIVE ORGANIZATION DURING THE DAY WITH DEEP CONVECTION RESTRICTED TO THE NORTHERN QUADRANT. AN UPPER LEVEL TROUGH AXIS IS NOW LOCATED JUST WEST OF THE SURFACE CYCLONE...WHICH IS THUS EXPERIENCING 30-40 KT OF VERTICAL SHEAR ACCORDING TO THE CIMSS ANALYSES. ADDITIONALLY...A COLD FRONTAL BOUNDARY TO THE NORTH OF THE CYCLONE IS INTERACTING WITH THE CYCLONE...WHICH IS SHOWN AS INCREASED BAROCLINICITY OF THE SYSTEM AS ANALYZED BY THE FSU CYCLONE PHASE SPACE DIAGRAMS. THE HIGHER SHEAR...INCREASED BAROCLINICITY...ALONG WITH THE RATHER COOL 19C SSTS SUGGEST THAT THE SYSTEM HAS LITTLE CHANCE AT THIS POINT TO BECOME A NAMED SUBTROPICAL STORM. THE CYCLONE WILL BEGIN MOVING TO THE SOUTHWEST IN THE NEXT COUPLE OF DAYS AS IT WEAKENS. ...THE ITCZ... THE ITCZ EXTENDS FROM THE LIBERIA COAST NEAR 6N11W TO 2N21W TO 4N37W TO 3N51W AT THE NE BRAZIL COAST. A WEAK TROUGH OF LOW PRESSURE IS EMBEDDED ALONG THE ITCZ AT 42W FROM 1N TO 9N. FROM 6N11W TO 2N30W TO 1N50W. SCATTERED MODERATE CONVECTION IS OBSERVED NEAR THE TROUGH AXIS. ELSEWHERE...WIDELY SCATTERED SHOWERS ARE WITHIN 180 NM OF THE ITCZ AXIS. ...DISCUSSION... GULF OF MEXICO... AS OF 21 UTC...A FRONTAL BOUNDARY IS DRAPED ACROSS THE GULF EXTENDING FROM THE FLORIDA PANHANDLE SW TO THE BAY OF CAMPECHE. N OF 24N THE BOUNDARY IS A COLD FRONT...WHILE TO THE SOUTH THE BOUNDARY IS A STATIONARY FRONT. WINDS ARE NORTH TO NORTHEAST UP TO 20 KT WEST OF THE FRONT AND SOUTHERLY GENERALLY 10 KT EAST OF THE FRONT. WIDELY SCATTERED CONVECTION IS FOUND ALONG THE FRONT NORTH OF 25N WITH MODERATE CONVECTION OCCURRING WEST OF SOUTH FLORIDA AHEAD OF THE FRONT. IN THE UPPER LEVELS... WEST-SOUTHWESTERLY FLOW PREVAILS RANGING FROM 25 KT IN THE SOUTHERN GULF UP TO 90 KT ALONG THE US GULF COAST. AT THE SURFACE...THE COOL AIR PUSH BEHIND THIS FRONT IS LIKELY TO BE SHORT-LIVED AND SHOULD RELAX TOMORROW. HOWEVER...A VIGOROUS COLD FRONT WILL ENTER THE NW GULF EARLY TUESDAY MORNING...SPREADING ACROSS THE GULF AND THE FLORIDA PENINSULA BY TUESDAY AFTERNOON...AND BRINGING GALE FORCE WINDS TO THE WESTERN GULF. STRONG NORTHERLIES WILL PREVAIL ON WEDNESDAY...BUT WILL MODERATE AS NORTHEASTERLIES ON THURSDAY. CARIBBEAN SEA THROUGHOUT THE CARIBBEAN...TYPICALLY TRANQUIL CONDITIONS PREVAIL. STRONGLY SUBSIDENT FLOW IS BEING CAUSED BY AN UPPER LEVEL RIDGE CENTERED JUST SOUTH OF HISPANIOLA. THE MODERATELY STRONG TRADEWINDS OVER THE CENTRAL CARIBBEAN YESTERDAY HAVE WEAKENED DOWN TO 20 KT AS THE SURFACE PRESSURE GRADIENT HAS RELAXED. NO LARGE-SCALE AREAS OF DEEP CONVECTION ARE OCCURRING CURRENTLY. HOWEVER...THE AFOREMENTIONED VIGOROUS COLD FRONT WILL REACH THE NW CARIBBEAN TUESDAY NIGHT BRINGING MODERATE NORTH TO NORTHEAST WINDS TO THE WESTERN THIRD OF THE CARIBBEAN ON WEDNESDAY AND THURSDAY. SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD AND ALONG THE FRONTAL BOUNDARY AS IT PUSHES THROUGH THE REGION. ATLANTIC ASIDE FROM THE SURFACE CYCLONE IN THE NE ATLANTIC DESCRIBED IN THE SPECIAL FEATURE SECTION ABOVE...THE REMAINDER OF THE REGION IS COVERED BY RIDGING AND EASTERLY FLOW OF UP TO 20 KT ALONG THE EQUATORWARD SIDE OF A SURFACE RIDGE NORTH OF 30N. IN THE UPPER LEVELS...A SHARP TROUGH EXTENDS FROM 27N37W SOUTHWESTWARD TO 14N53W. NUMEROUS BUT WIDELY SCATTERED SHOWERS AND EXTENSIVE UPPER LEVEL CLOUDINESS EXIST SOUTH OF THE TROUGH AXIS. THE AFOREMENTIONED STRONG COLD FRONT WILL ENTER THE W ATLANTIC TUESDAY NIGHT...REACH ABOUT 65W WEDNESDAY NIGHT ALONG 30N...AND EXTEND TO ABOUT 55W THURSDAY NIGHT ALONG 30N. AT THIS POINT...GALE FORCE WINDS IN THE ATLANTIC ARE NOT EXPECTED BECAUSE OF THIS FRONT. $$ CWL