000 AXNT20 KNHC 291810 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 105 PM EST FRI DEC 29 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. ...CORRECTION TO INTRODUCE SPECIAL FEATURE... BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC ...SPECIAL FEATURE... INTERESTING FEATURE FOR THE DAY IS THE DEEP CYCLONE CENTERED NEAR 27N38W. THIS SYSTEM HAS REMAINED STATIONARY FOR A COUPLE OF DAYS AND ORGANIZED CONVECTION IS DEVELOPING IN A COUPLE OF BANDS LOCATED TO THE EAST OF THE CENTER. QUIKSCAT WINDS SUGGEST THAT THERE ARE SOME GALE FORCE WINDS ALONG THE NORTHERN SEMI-CIRCLE AND SE QUADRANT OF THE SYSTEM...THAT SEEMS TO BE ACQUIRING SOME SUBTROPICAL CHARACTERISTICS. THE MOST COMMON TYPE OF SUBTROPICAL CYCLONE IS AN UPPER-LEVEL COLD LOW WITH CIRCULATION EXTENDING TO THE SURFACE...AS IN THIS CASE. ACCORDING TO THE UW-CIMSS PRODUCTS...VERTICAL SHEAR ON THE SYSTEM IS RELATIVELY WEAK...BUT THIS LOW-MODERATE SHEAR ENVIRONMENT MAY ONLY LAST FOR ANOTHER DAY OR SO BEFORE STRONG UPPER WESTERLIES IMPACT THE SYSTEM WITH THE APPROACH OF A VIGOROUS SHORT-WAVE TROUGH. THE CYCLONE SHOULD MEANDER IN PLACE FOR THE NEXT 24-36 HOURS OR SO. SOME OF THE MODEL GUIDANCES MOVE THIS SYSTEM TO THE SW ACROSS THE OPEN OCEAN WATERS. THIS SYSTEM COULD BECOME A SUBTROPICAL CYCLONE AT ANY TIME. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 5N10W 3N20W 3N35W EQUATOR AT 42W INTO NE BRAZIL NEAR 2S45W. AT THIS POINT THERE ARE CLUSTERS OF MODERATE CONVECTION. SCATTERED MODERATE CONVECTION IS WITHIN 170 NM N OF THE ITCZ AXIS BETWEEN 15W-35W. ...DISCUSSION... THE GULF OF MEXICO... AS OF 1500 UTC...THE COLD FRONT THAT ENTERED THE REGION YESTERDAY HAS STALLED OVER THE CENTRAL GULF AND NOW EXTENDS AS A STATIONARY FRONT FROM THE FLORIDA PANHANDLE ALONG 25N94W TO THE BAY OF CAMPECHE...THEN CONTINUES ALONG THE EASTERN SLOPES OF THE SIERRA MADRE MOUNTAINS. A NARROW LINE OF SHOWERS WITH EMBEDDED TSTMS MARKS THE LEADING EDGE OF THE FRONT. IN THE MID AND UPPER LEVELS...SOUTHWESTERLY FLOW DOMINATES THE AREA ADVECTING A PLUME OF MOISTURE FROM THE EPAC ACROSS THE DEEP SOUTH IN TEXAS TO THE SE U.S..AN UPPER TROUGH OVER THE CENTRAL PLAINS SUPPORTS THE ABOVE MENTIONED FRONTAL BOUNDARY. A SURFACE RIDGE EXTENDS FROM THE ATLC INTO THE EASTERN GULF THROUGH THE FLORIDA PENINSULA GIVING THE AREA MOSTLY FAIR WEATHER...WARM TEMPERATURES AND SELY WIND FLOW. NEAR RECORD OR RECORD-BREAKING AFTERNOON HIGH TEMPERATURES ARE EXPECTED IN SOUTH FLORIDA DUE TO THIS WEATHER PATTERN. THIS RIDGE IS ALSO BLOCKING THE MOVEMENT OF THE FRONT BUT IS FORECAST TO MOVE SE TONIGHT INTO SUN...ALLOWING THE FRONT TO MOVE AGAIN SE BEFORE BECOMING DIFFUSE AND DISSIPATE MON. LOOKING AHEAD...A STRONGER COLD FRONT IS IN STORE FOR THE BEGINNING OF THE NEW YEAR. THIS FRONT IS EXPECTED TO MOVE RAPIDLY OFF THE TEXAS COAST LATE MON AND EXTEND FROM THE FLORIDA PANHANDLE TO BAY OF CAMPECHE EARLY TUE FOLLOWED BY STRONG NLY FLOW AND MUCH COOLER TEMPERATURES. GALE FORCE WINDS ARE EXPECTED OVER THE WESTERN GULF TUE AND WED WHEN THE COLD FRONT IS EXPECTED TO MOVE ACROSS SOUTH FLORIDA. THE CARIBBEAN SEA... LITTLE CHANGE HAS EXPERIENCED THE WEATHER PATTERN ACROSS THE CARIBBEAN SEA. THE AREA REMAINS UNDER THE INFLUENCE OF A MID TO UPPER-LEVEL RIDGE WHICH IS PRODUCING STRONG SUBSIDENCE AND IMPLIED DRY AIR. THIS RIDGE...ANCHORED ON A HIGH OVER EASTERN CUBA ALSO COVERS CENTRAL AMERICA...SOUTHERN MEXICO AND THE SE PORTION OF THE GULF OF MEXICO. SOME HIGH CLOUDS ARE MOVING NWD ON THE WESTERN PERIPHERY OF THE RIDGE FROM CENTRAL AMERICA TO WESTERN CUBA. AT THE SURFACE...POCKETS OF LOW LEVEL MOISTURE WITH EMBEDDED LIGHT TO MODERATE SHOWERS ARE ROTATING AROUND THE SURFACE HIGH LOCATED WELL N OF THE AREA. THIS FEATURE CURRENTLY COVERS MOST OF THE WEST AND CENTRAL ATLC. A DIFFERENCE IN PRESSURE BETWEEN THE HIGH AND THE COLOMBIAN LOW...ANALYZED 1009 MB NEAR 10N77W IS PRODUCING A SWATH OF 20 TO 30 KT ELY WINDS ACROSS THE CARIBBEAN SEA WITH THE STRONGEST WINDS PER USUAL JUST OFF THE COLOMBIAN COAST. MODERATE TO STRONG TRADE WINDS WILL PERSIST ACROSS THE SEA THROUGH MONDAY. THE ATLANTIC OCEAN... A 1008 MB LOW IS NEAR 27N38W. SEE SPECIAL FEATURE ABOVE FOR DETAILS. ELSEWHERE...THE W ATLC REMAINS DOMINATED BY RIDGING WITH THE MID AND UPPER AXIS EXTENDING NWD FROM THE CARIBBEAN THROUGH BERMUDA. A JETSTREAM BRANCH IS RIDING ON THE N PERIPHERY OF THIS ANTICYCLONE BRINGING SOME UPPER LEVEL MOISTURE/HIGH CLOUDS INTO THE W ATLC...BUT MAINLY N OF 30N. AN UPPER TROUGH ALSO REMAINS STUCK OVER THE CENTRAL ATLANTIC EXTENDING SW FROM A CUT-OFF LOW NEAR 27N38W TO THE WINDWARD ISLANDS. A TROPICAL JETSTREAM RUNS FROM THE BASE OF THIS TROUGH ALL THE WAY TO THE NE TO THE WEST COAST OF AFRICA CROSSING JUST N OF THE CAPE VERDE ISLANDS. WV IMAGERY SHOWS A BAND OF TRANSVERSE HIGH CLOUDS ASSOCIATED WITH THE JET. $$ GR