000 AXNT20 KNHC 121800 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT WED MAR 12 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 7N12W 2N20W CROSSING THE EQUATOR NEAR 26W TO 5S36W. CLUSTERS OF SCATTERED MODERATE/ STRONG CONVECTION ARE OCCURRING FROM THE COAST OF SW AFRICA TO S TO THE EQUATOR BETWEEN 2E AND 23W. ADDITIONAL SCATTERED LIGHT/MODERATE CONVECTION IS ACTIVE FROM THE EQUATOR TO 2N BETWEEN 26W AND 30W. ...DISCUSSION... GULF OF MEXICO... A VIGOROUS SRN STREAM SHORTWAVE TROUGH NEAR THE CENTRAL GULF COAST THIS MORNING SHOULD DART EAST INTO THE WRN ATLC AND WEAKEN BY EARLY THU. AS IT DOES SO...THE IMPULSE SHOULD HELP DRAG A WEAK COLD FRONT CURRENTLY EXTENDING FROM 31N74W TO 26N83W THROUGH THE FL PENINSULA TODAY AND THROUGH THE CENTRAL BAHAMAS BY LATE THU. THE SOUTHERN END OF THE FRONT EXTENDING FROM 26N83W TO 20N93W AND THEN SOUTHWARD THROUGH THE ISTHMUS OF TEHUANTEPEC SHOULD REMAIN ESSENTIALLY STATIONARY OR SLOWLY EDGE SE...AS THE MAIN UPR SUPPORT QUICKLY HEADS EAST OF THE AREA AND THE MID- TO UPPER-LEVEL WINDS BECOME PARALLEL TO THE FRONT. 1046 UTC AND 1226 UTC QUIKSCAT PASSES OVER THE GULF REVEAL A WEAK WIND REGIME OVER THE AREA...WITH THE HIGHEST WINDS OF 10 TO 15 KT DIRECTLY BEHIND THE FRONT AND IN EXTREME ERN GULF AND IN THE SW GULF/BAY OF CAMPECHE. SATELLITE IMAGERY REVEALS SCATTERED MOSTLY LOW- TO MID-LEVELS CLOUDS OVER THE BAY OF CAMPECHE...WHERE EASTERLY TRADES MEET NORTHERLY FLOW BEHIND THE FRONT. LOW CLOUDS ARE ALSO BANKED UP AGAINST THE SIERRA MADRE OCCIDENTAL IN MEXICO... REFLECTING A CONTINUED WEAK UPSLOPE FLOW. FARTHER UPSTREAM....AN ILL-DEFINED SHORTWAVE TROUGH PASSING THROUGH THE SW CONUS/NRN MEXICO SHOULD PUSH INTO THE SRN PLAINS THU...WHILE A STRING OF AMORPHOUS SHORTWAVE ENERGY PROPAGATES OUT OF THE CENTRAL ROCKIES. IN RESPONSE TO THESE DEVELOPMENTS ALOFT...A 1022 MB SURFACE RIDGE CURRENTLY NEAR THE CENTRAL TX COAST SHOULD MIGRATE RAPIDLY EWD TO NRN FLORIDA BY THU MORNING AND BE REPLACED WITH A STRENGTHENING RETURN FLOW OVER THE WRN HALF OF THE GULF AS LOW PRESSURE FORMS IN THE SRN PLAINS. FALLING HEIGHTS AND A PATTERN OF WARM AIR ADVECTION OVER THE SRN PLAINS/WRN GULF COAST SHOULD FORCE THE NEARLY STATIONARY BOUNDARY PRESENTLY OVER THE SOUTHERN GULF TO RETURN AS A WARM FRONT EITHER LATE TONIGHT OR EARLY THU MORNING. EXPECT OVERRUNNING CLOUDS AND THE CHANCE FOR SCATTERED SHOWERS AND ISOLATED TSTMS NEAR AND NORTH OF THE BOUNDARY...WHICH SHOULD LIFT TO NEAR THE NRN GULF COAST BY FRI MORNING. CARIBBEAN SEA... A FLAT BUT BROAD...MID- TO UPPER-LEVEL ANTICYCLONE LYING JUST OF THE LESSER ANTILLES DOMINATES MUCH OF THE CARIBBEAN BASIN THIS MORNING...WITH A RIDGE AXIS BETWEEN 16-17N. WATER VAPOR IMAGERY INDICATES THAT STRONG SUBSIDENCE ALOFT ASSOCIATED WITH THIS FEATURE COVERS THE ENTIRE REGION...WITH THE STRONGEST SUBSIDENCE CONCENTRATED OVER THE SW CARIBBEAN SEA. THE SAN JUAN 12 UTC SOUNDING SHOWS A STRONG TRADE WIND INVERSION AROUND 750MB...WITH EXTREMELY STABLE AND DRY AIR ABOVE THAT LEVEL. AS A RESULT... THERE ARE FEW IN THE WAY OF CLOUDS OR SHOWERS ACROSS THE CARIBBEAN THIS MORNING EXCEPT FOR SOME FROM 15N AND 18N BETWEEN 70W AND 77W. A STRONG ZONAL FLOW NORTH OF THE CARIBBEAN HAS LED TO A BREAK DOWN OF THE STRONG LOW-LEVEL SUBTROPICAL RIDGE...WHICH HAD PERSISTED FROM THE CENTRAL ATLC INTO THE CARIBBEAN SEA FOR MUCH OF THE FIRST WEEK OF MARCH. CONSEQUENTLY....TRADES ACROSS THE CARIBBEAN ALSO REMAIN WEAK...ESPECIALLY WHEN COMPARED TO THE ANOMALOUSLY STRONG TRADE WIND CONDITIONS DURING THE LAST SEVERAL WEAK. A 1046 UTC QUIKSCAT PASS SHOWS THE STRONGEST WINDS OF 15 TO 20 KT GENERALLY S OF 16N BETWEEN 70W AND 79W. AS IS TYPICAL ...STRONGER WINDS OF UP TO 25 KT LIE NEAR BUT OFFSHORE THE COAST OF COLOMBIA. THE LIGHTEST WINDS LIE OVER THE NW PART OF THE BASIN...WHERE LIGHT NE TO E WINDS OF 5 TO 10 KT HAVE DEVELOPED IMMEDIATELY AHEAD OF THE COLD FRONT DRIFTING SEWD ACROSS THE SRN GULF. EXPECT A WEAK TRADE WIND REGIME TO CONTINUE THROUGH AT LEAST FRI BEFORE SHOWING SIGNS OF RESTRENGTHENING SOME LATER THIS WEEKEND. ATLANTIC OCEAN... THE SHORTWAVE TROUGH ACROSS THE GULF THIS MORNING IS PUSHING A COLD FRONT INTO THE SW ATLC AND DOWN THE STATE OF FL...WHILE LIFTING A WARM FRONT AROUND 30N BETWEEN 65W AND 74W NORTH OF THE AREA. ALTHOUGH FEW...IF ANY...CLOUDS DEFINE THE COLD FRONT OVER FL...UPPER-LEVEL DIVERGENCE AND RIGHT REAR JET DYNAMICS NORTH OF THE BAHAMAS ARE FORCING SCATTERED MODERATE TO NUMEROUS SHOWERS AND TSTMS AHEAD OF IT...WITHIN 90NM EITHER SIDE OF A LINE RUNNING FROM 31N69W TO 28N75W. IN ADDITION...A 1046 UTC QUIKSCAT PASS REVEALS 25- TO 30-KT SWLY FLOW WITHIN ABOUT 120NM SE OF THE FRONT N OF 28N. MODEL GUIDANCE SHOWS THE FRONT CONTINUING EWD TODAY AND TONIGHT...ENDING UP ALONG AN AXIS FROM 31N61W TO 26N76W TO 23N78W BY THU MORNING...WITH STRONG SWLY FLOW LIKELY PRECEDING IT THROUGH THU. ANOTHER FRONT EXTENDS FROM 31N43W TO 28N56W...WHERE IT ATTACHES ITSELF TO THE WARM FRONT LIFTING NE OVER THE SW ATLC. THE FRONT SHOULD CONTINUE EWD TODAY...MOVING EAST OF THE AREA BY THU WITH LITTLE FANFARE. OTHERWISE...THE TAIL OF A SHORTWAVE TROUGH EAST OF THE AREA THIS MORNING EXTENDS THROUGH 15N39W AND FINALLY TO 12N60W. THIS FEATURE SHOULD EXIT THE AREA ENTIRELY BY THU EVENING...LEAVING THE BROAD BUT FLAT MID- TO UPPER-LEVEL RIDGE OVER THE CARIBBEAN TO EWD 30W BUT SOUTH OF 20N. THIS PATTERN FAVORS ANOMALOUS EASTERLY FLOW AT 200MB SOUTH OF ABOUT 16N FROM THE TROPICAL ATLC THROUGH MUCH OF THE CARIBBEAN SEA AND IS THOUGHT TO BE RELATED TO THE STRONG AND MATURE LA NINA EVENT IN THE PACIFIC. $$ KIMBERLAIN