000 AXNT20 KNHC 111747 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT TUE MAR 11 2008 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 1745 UTC. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 7N13W 4N20W CROSSING THE EQUATOR NEAR 26W THEN ALONG 2S30W TO 3S41W. CLUSTERS OF SCATTERED MODERATE/STRONG CONVECTION ARE FROM 1W-14W BETWEEN THE THE COAST OF SW AFRICA TO ACROSS THE EQUATOR. SCATTERED MODERATE CONVECTION IS WITHIN 75 NM OF 5N W FROM 47-51W TO INLAND OVER SOUTH AMERICA. ...DISCUSSION... GULF OF MEXICO... A WEAK SHORTWAVE TROUGH OVER THE LOWER MISSISSIPPI VALLEY THIS MORNING SHOULD TREK EAST-NORTHEAST AND BECOME ABSORBED BY A MORE DOMINANT NORTHERN STREAM SHORTWAVE EARLY WEDNESDAY. AS IT DOES SO...IT SHOULD HELP DRAG A WEAK ASSOCIATED COLD FRONT LOCATED ALONG 29N89W 28N90W 24N93W 20N97W THROUGH THE REMAINDER OF THE WESTERN AND CENTRAL GULF LATER TODAY AND THIS EVENING AND CARRY AN ASSOCIATED 1018MB SURFACE LOW FROM 29N90W INTO THE NE GULF. HOWEVER...THE COLD SHOULD ONLY MAKE SLOW SEWD PROGRESS TONIGHT AND EARLY...UNTIL A SECOND SOUTHERN STREAM SHORTWAVE MOVING THROUGH THE SOUTHERN PLAINS REACHES THE GULF COAST EARLY WED AND DRIVES THE FRONT THROUGH THE REMAINDER OF THE GULF AND FLORIDA TO A POSITION 31N70W 22N81W 21N88W EARLY WED AFTERNOON. A PATTERN OF WEAK...LARGE-SCALE DIVERGENCE ALOFT...RIGHT REAR QUADRANT DYNAMICS...AND OVERRUNNING MOISTURE AHEAD OF THIS SYSTEM IS DRIVING SCATTERED LIGHT TO MODERATE CONVECTION FROM NEAR THE MOUTH OF THE MS RIVER THIS MORNING TO THE FLORIDA PANHANDLE. ADDITIONAL SHOWERS AND TSTMS ARE DEVELOPING IN THE BAY OF CAMPECHE AND SW GULF...WHERE THE ELY TRADES ARE MEETING THE NLY FLOW BOTH AHEAD AND BEHIND THE FRONT. FARTHER EAST... SHOWERS AND TSTMS HAVE ALSO BROKEN OUT FROM NEAR THE DRY TORTUGAS THROUGH THE LOWER FLORIDA KEYS AND FLORIDA BAY...AHEAD OF WHAT ONCE WAS LIKELY THE OLD POLAR FRONT. HOWEVER...LOW-LEVEL WINDS SHOW LITTLE...IF ANY CYCLONIC SHEAR AT THIS TIME...WHICH MAY SUGGEST THAT THIS CONVECTION IS DEVELOPING NEAR AND AHEAD OF THE 850MB FRONT BEING TO RETURN NEWD. AS THE SECOND SRN STREAM SHORTWAVE RIDES THROUGH N FL LATE WED...THE COLD FRONT SHOULD CONTINUE EWD THROUGH SW ATLC BUT BECOME STATIONARY THROUGH THE SRN GULF. NEW HEIGHT FALLS AHEAD OF YET ANOTHER SHORTWAVE PUSHING THROUGH THE ROCKIES SHOULD CAUSE THE WRN PORTION OF THE BNDRY TO RETURN AS A WARM BY THU...WITH MODEL GUIDANCE SUGGESTING A FAIR AMOUNT OF CONVECTION FORMING AHEAD OF THE RETREATING BOUNDARY OVER THE WEST CENTRAL GULF. CARIBBEAN SEA... A FLAT MID- TO UPPER-LEVEL RIDGE OF HIGH PRESSURE COVERS THE BASIN...WITH AN AXIS ALONG 15N-16N. DEEP 200MB EASTERLIES...AND ANOMALOUS EASTERLIES AT THAT... EXIST SOUTH OF THE RIDGE AXIS COVER MUCH OF NRN SOUTH AMERICA AND THE SOUTHERN CARIBBEAN. THIS PATTERN OF ELY UPPER-LEVEL FLOW DEVELOPING SO EARLY COULD BE PARTIALLY RELATED TO THE STRONG COLD EVENT OCCURRING IN THE PACIFIC. ELSEWHERE...STRONG ZONAL FLOW ALOFT FROM FLORIDA THROUGH THE WESTERN ATLANTIC HAS RESULTED IN LOWER SURFACE PRESSURES OVER THE AREA COMPARED TO LAST WEEK AND THIS WEEKEND. THE RESULT HAS BEEN A BREAK IN THE MODERATE TO STRONG SURFACE RIDGE WHICH HAS BEEN IN PLACE FOR MUCH OF THE FIRST WEEK OF MARCH. IN TURN...THIS HAS LED TO A GENERAL REDUCTION OF THE TRADE WIND FLOW BASIN WIDE EARLY THIS WEEK...WITH 15- TO 20-KT WINDS IN PLACE OF 20- TO 25-KT WINDS. EVEN WINDS OFF THE COAST OF COLOMBIA HAVE DECREASED MARKEDLY...WITH 20- TO OCCASIONALLY 25-KT WINDS INSTEAD OF 30-KT WINDS. OTHERWISE...THE GULF FRONT DESCRIBED ABOVE SHOULD REACH THE NE YUCATAN/YUCATAN CHANNEL EARLY WED AND COME TO A HALT AS 500MB HEIGHTS BEGIN RISING OVER THE GULF AHEAD OF A NEW JET STREAM IMPULSE MOVING OUT OF THE WEST. ATLANTIC OCEAN... A NRN STREAM SHORTWAVE...EXTENDING FROM EAST OF THE CANADIAN MARITIMES SOUTHWESTWARD INTO THE WRN ATLC...IS DRIVING AN ASSOCIATED COLD FRONT ALONG 31N54W 28N60W SLOWLY EWD. MEANWHILE...THE SRN END OF THE BOUNDARY REMAINS STATIONARY FROM 28N60W TO 24N77W BUT SHOULD BEGIN LIFTING NORTH AND EAST AS A WARM FRONT LATER TODAY AND WED IN RESPONSE TO A SHORTWAVE MOVING OUT OF THE SRN PLAINS TO THE NE GULF COAST DURING THE NEXT 24 HOURS. WARM AIR ADVECTION...OVERRUNNING MOISTURE...AND POSITIVE VORTICITY ADVECTION AHEAD OF THIS JET STREAM DISTURBANCE SHOULD LEAD TO SCATTERED CONVECTIVE ACTIVITY NORTH OF THE RETREATING BOUNDARY...FIRST OVER THE SOUTHERN HALF OF FLORIDA AND THE NWRN BAHAMAS AND THEN ULTIMATELY FARTHER NE. CONVECTIVE STORMS SHOULD ALSO FIRE UP AHEAD OF THE COLD FRONT MOVING OFF THE FL COAST EARLY WED AND AFTERNOON AND REMAIN SCATTERED ALONG THE BOUNDARY...AS IT BECOMES STATIONARY OVER THE CENTRAL BAHAMAS THU AFTERNOON. THE NRN END OF THE BOUNDARY CURRENTLY OVER THE BAHAMAS SHOULD CONTINUE TRACKING EWD WED AND THU...LYING FROM 31N39W TO 27N51W BY WED AFTERNOON AND FROM 31N30N TO 28N39W THU AFTERNOON. ELSEWHERE...MID- TO UPPER-LEVEL HIGH PRESSURE OVER THE CARIBBEAN TODAY SHOULD BUILD EWD INTO THE TROPICAL ATLC MIDDLE AND LATE WEEK...REPLACING THE CURRENT SHORTWAVE TROUGH LYING FROM 28N41W TO 11N60W. THIS SHOULD PROMOTE AN ANOMALOUS ELY FLOW REGIME AT UPPER-LEVELS SOUTH OF 10N ACROSS MUCH OF THE TROPICAL ATLC. IN ADDITION... LOW-LEVEL RIDGING OVER THE SUBTROPICAL ATLC HAS WEAKENED SUBSTANTIALLY SINCE LAST WEEK AND THIS WEEKEND...WITH WHAT REMAINS OF THE RIDGE STRONGEST OVER THE EXTREME ERN PART OF THE BASIN. THIS HAS RESULTED IN A GENERAL RELAXATION OF ELY TRADES S OF 20N...WITH TRADES AT OR BELOW CLIMATOLOGICAL LEVELS. $$ KIMBERLAIN