000 AXNT20 KNHC 141803 TWDAT TROPICAL WEATHER DISCUSSION... NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON APR 14 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... THE ITCZ AXIS IS CENTERED ALONG 5N08W 2N19W EQ30W TO NE BRAZIL NEAR 1S46W. A LARGE CLUSTER OF MODERATE TO STRONG CONVECTION IS WITHIN 150 NM EITHER SIDE OF AXIS BETWEEN 14W AND 20W. SCATTERED MODERATE ISOLATED/STRONG CONVECTION IS WITHIN 150 NM N OF AXIS AND 60 NM S OF AXIS BETWEEN 27W AND 37W. SCATTERED MODERATE CONVECTION LIES BETWEEN 01N AND 04 BETWEEN 42W AND 50W. ...DISCUSSION... THE GULF OF MEXICO... A STRONG SHORTWAVE TROUGH DIGGING INTO THE SE U.S. DROVE A COLD FRONT THROUGH THE GULF YESTERDAY AND LAST NIGHT...BUT SURFACE ANALYSES INDICATE A SECOND...STRONGER SURGE EXTENDING FROM NEAR TAMPA WSW THROUGH NE MEXICO SWEEPING S AND E ACROSS THE REGION AS OF 1500 UTC. AN 1132 UTC QUIKSCAT PASS PROVIDED SOME PROOF AS TO THE LOCATION OF THE SECOND FRONT...GIVEN BY A BROAD CYCLONIC SHEAR AND A MARGINAL INCREASE IN WINDS N OF THE BOUNDARY. MOREOVER...VISIBLE SATELLITE IMAGERY SHOWS A DISTINCT ROPE-LIKE BAND OF CLOUDS AT THE LEADING EDGE OF THE FRONT JUXTAPOSED WITH NEARLY CLEAR SKIES OVER THE SOUTHERN GULF SAVE FOR LOW CLOUDS BANKED UP THE HIGHER TERRAIN OF THE SIERRA MADRE ORIENTAL. INTERESTINGLY...DESPITE THE HIGHER MID-APRIL SUN ANGLE ...COLD AIR ADVECTION BEHIND THE FRONT IS ENOUGH TO KEEP TEMPERATURES THE SAME OR FALLING AT THIS HOUR OF THE DAY. MOSTLY NW TO N WINDS OF 15 TO 20 KT COVER MOST OF THE CENTRAL AND WESTERN GULF...WITH A MINOR MINIMUM IN WINDS IMMEDIATELY N OF THE SECONDARY BOUNDARY. FULLY DEVELOPED SEAS OF 6 TO 10 FT ARE COMMON OVER MOST OF THE GULF EXCEPT 4 TO 7 FT OVER THE EASTERN GULF...WITH SEAS GRADUALLY SUBSIDING AFTER PEAKING LATE YESTERDAY. MODELS SHOW THE SHORTWAVE OVER THE SE U.S. CUTTING OFF OVER THE WESTERN ATLANTIC EARLY THIS WEEK AND PERSISTING OVER THE REGION. THIS SHOULD KEEP THE POLAR BOUNDARY WELL S AND E OF THE AREA... WITH HIGH PRESSURE...FAIR SKIES...AND DRY WEATHER REIGNING ACROSS THE GULF THROUGH LATE WEEK. A NW TO N FLOW TODAY SHOULD DECREASE AND BECOME E TO SE OVER THE CENTRAL AND WESTERN GULF BY MID-WEEK...WHICH SHOULD LED TO AN INCREASE IN LOW-LEVEL MOISTURE OVER THE WESTERN GULF BY WED. THE CARIBBEAN SEA... THE SAME VIGOROUS SHORTWAVE DIGGING INTO THE SOUTHEASTERN STATES HAS HELPED DRAG THE FRONT WHICH SWEPT ACROSS THE GULF YESTERDAY INTO THE NW CARIBBEAN...LYING FROM 21N78W TO 17N88W AS OF 1500 UTC. AS THE SECONDARY FRONT DESCENDS WELL INTO THE GULF...THE PRIMARY BOUNDARY HAS NOTICEABLY SLOWED DOWN BUT IS STILL ON THE MOVE...ALBEIT IT BARELY. VISIBLE SATELLITE IMAGERY REVEALS SCATTERED LOW CLOUDS LINING THIS FEATURE...FOLLOWED BY A NEARLY SOLID AREA OF STRATUS HOVERING OVER THE YUCATAN CHANNEL...NE TIP OF THE YUCATAN...AND THE WESTERN CUBA. SHIP REPORTS AND AN EARLIER QUIKSCAT PASS SHOWED INCREASING N TO NE WINDS OF 15 TO 20 KT ARE N OF THE FIRST FRONT...WITH THE HIGHEST WINDS NOTED IN THE VICINITY OF THE YUCATAN CHANNEL. AS THE SHORTWAVE MOVING OFFSHORE THE SE U.S. DIGS INTO THE WESTERN ATLANTIC AND CUTS OFF TUE...THE SECONDARY FRONT SHOULD CATCH UP TO THE FIRST. THE CONSOLIDATED FRONTAL BOUNDARY SHOULD PUSH AS FAR SE AS A WINDWARD PASSAGE-CAPE GRACIAS A DIOS NICARAGUA LINE BY LATE TUE...WHERE IT IS FORECAST TO BECOME STATIONARY AND THEN DISSIPATE BY FRI. A BRISK NE FLOW N OF THE FRONT SHOULD CAUSE SEAS TO BUILD TO 5 TO 8 FT IN N SWELL...WITH SCATTERED LOW CLOUDS ALONG THE BOUNDARY AND A FEW SHOWERS DECREASING AS THE BOUNDARY LOSES ITS IDENTITY. ELSEWHERE...WEAK LOW- TO MID-LEVEL HIGH PRESSURE EXTENDS FROM THE CENTRAL ATLANTIC SW INTO THE CENTRAL CARIBBEAN AND IS KEEPING TRADES NEAR OR BELOW CLIMATOLOGICAL AVERAGES FOR THE TIME BEING. THIS IS ESPECIALLY TRUE WITHIN ABOUT 400 NM SE OF THE NW CARIBBEAN FRONT TODAY...WHERE QUIKSCAT DATA INDICATE N TO NE WINDS OF ONLY 5 TO 10 KT EXCEPT S OF JAMAICA. VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS ALSO SUGGEST THE PRESENCE OF WHAT COULD BE A WEAK LOW-LEVEL TROUGH EXTENDING FROM 14N72W TO PUERTO RICO AND THE U.S. VIRGIN ISLANDS. TIME SERIES DATA FROM SAN JUAN AND OTHER SURROUNDING SITES CORROBORATE THE EXISTENCE OF THIS FEATURE...BUT AS WITH MOST OTHER METRICS... THESE DATA SUGGEST A FAIRLY WEAK SIGNATURE. STILL THOUGH... LOW-LEVEL MOISTURE E OF THE BOUNDARY HAS INCREASED AS REVEALED IN THE MOST RECENT SAN JUAN SOUNDING...WHERE 70-90 PER CENT RELATIVE HUMIDITY HAS GONE FROM AT OR BELOW 850MB TWO DAYS AGO TO 700 MB TODAY. WITH HEIGHTS COLLAPSING OVER THE NW CARIBBEAN W ATLANTIC EARLY THIS WEEK...TRADES SHOULD CONTINUE WEAK THROUGH MIDDLE AND LATE WEEK AND SEAS CONTINUING TO RUN FROM 4 TO 7 FT EXCEPT LOCALLY HIGHER IMMEDIATELY OFFSHORE THE COLOMBIAN COAST. THE WEAK LOW-LEVEL TROUGH SHOULD CONTINUE WESTWARD AT 10 TO 15 KT AND EVENTUALLY MERGE WITH THE STATIONARY FRONTAL BOUNDARY BY LATE TUE. THE ATLANTIC OCEAN... THE SAME SHORTWAVE TROUGH DIGGING INTO THE SE U.S. TODAY IS RESPONSIBLE FOR CARRYING A FRONTAL BOUNDARY ACROSS FL LAST NIGHT ...WITH THE FRONT EXTENDING FROM 31N69W TO EAST CENTRAL CUBA AS OF 1500 UTC. VISIBLE SATELLITE IMAGERY CONFIRMS WHAT MODELS HAVE BEEN FORECASTING...THAT IS...THE DEVELOPMENT OF A 1012 MB FRONTAL WAVE LOCATED NEAR 27N74W...MOVING NE AT 15 TO 20 KT. NOT TOO FAR BEHIND...A STRONGER SECONDARY BOUNDARY HAS MOVED OFFSHORE THE NE FL COAST AND IS ON THE VERGE OF DESCENDING THROUGH THE NW BAHAMAS. AS THE SE U.S. SHORTWATE CUTS OFF TUE...EXPECT THE DEVELOPING FRONT WAVE TO SLOW DOWN...STRENGTHEN ...AND MOVE N OF THE AREA TO A POSITION OFFSHORE THE MID- ATLANTIC COAST. AS IT DOES SO...IT SHOULD DRAG A CONSOLIDATED COLD FRONT THROUGH THE REMAINDER OF THE BAHAMAS AND THE SW ATLANTIC...WITH THE FRONT LYING FROM 31N66W TO CENTRAL HISPANIOLA LATE WED. A BRISK NW FLOW BEHIND THE FRONT SHOULD VEER MORE NE...AS LOW PRESSURE RAPIDLY GATHERS STEAM OFF THE CAROLINA COAST AND RESULT IN SEAS BUILDING TO 9 TO 15 FT GENERALLY N OF 27N W OF 70W IN NE SWELL. LARGE BREAKERS SHOULD BEGIN ARRIVING OVER THE NW BAHAMAS AS WELL AS THE NE AND EAST CENTRAL FL COASTS LATE TUE AND WED. OTHERWISE...AN ANOMALOUS MID- TO UPPER-LEVEL RIDGE SHOULD SET UP SHOP N OF 17N E OF ABOUT 65W EARLY AND MID-WEEK. THIS SHOULD FAVOR A STRONGER SUBTROPICAL RIDGE OVER THE EASTERN AND CENTRAL ATLANTIC...WHICH SHOULD IN TURN LEAD TO A TRADE WIND FLOW CLOSER TO CLIMATOLOGY...COMPARED TO THE WEAK TO NON-EXISTENT TRADES FROM LAST WEEK. ALREADY EARLY MORNING QUIKSCAT PASSES ARE HINTING AT AN INCREASED NE FLOW BETWEEN 15N AND 20N E OF 45W... AND THESE WINDS SHOULD EXPAND FURTHER THROUGH MID-WEEK. $$ KIMBERLAIN