000 AXNT20 KNHC 102346 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU APR 10 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 05N09W 4N20W 1N30W 1N50W. SCATTERED MODERATE AND EMBEDDED STRONG CONVECTION IS TIGHTLY CLUSTERED WITHIN 150 NM N OF THE AXIS BETWEEN 17W AND 20W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM EITHER SIDE OF THE AXIS BETWEEN 31W-50W. ...DISCUSSION... GULF OF MEXICO... A LARGE MID- TO UPPER-LEVEL RIDGE EXTENDS FROM THE FL PENINSULA SW THROUGH THE BAY OF CAMPECHE AND DOMINATES MOST OF THE REGION WITH MODERATE TO STRONG SUBSIDENCE...ESPECIALLY S OF 24N E OF 92W. HOWEVER...UPPER TROPOSPHERIC SOUTHWESTERLY FLOW IS ON THE INCREASE OVER THE NW GULF...AS A STRONG CLOSED CYCLONE AND ASSOCIATED SHORTWAVE TROUGH MOVE OUT OF THE PLAINS AND INTO THE MIDWEST. THIS TROUGH IS PROVIDING SUPPORT FOR A COMPLEX 987 MB LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS...WITH AN ASSOCIATED COLD FRONT LOSING ITS IDENTITY AS IT ADVANCES THROUGH THE MS RIVER VALLEY THROUGH SE TX. THE PRESSURE GRADIENT BETWEEN LOW PRESSURE ON THE PLAINS AND A 1022 MB SURFACE RIDGE NEAR BERMUDA IS GENERATING A BRISK SE TO S RETURN FLOW OF 20- TO 25-KT W OF 84W. THE DURATION AND FETCH OF THIS SLY FLOW HAS BEEN FAIRLY CONSTANT SINCE LAST NIGHT...WHICH HAS HELPED SEAS TO BUILD UP TO 11 FT OVER THE NW WATERS. OTHERWISE...THE LATEST SURFACE ANALYSIS INDICATES AN ENE-WSW ORIENTED RIDGE ALONG OR JUST OFFSHORE THE NORTHERN GULF COAST...WITH AN AXIS EXTENDING FROM 30N85W TO 26N93W. ASIDE FROM A FEW SHALLOW CLOUDS OVER THE EAST CENTRAL GULF...FAIR WEATHER PREVAILS ACROSS THE REGION...BUT LOW- TO MID-LEVEL CLOUDS ALONG THE TX AND SW LA COASTS HERALD THE WEAKENING FRONT APPROACHING THE AREA. AS THE DEEP TROUGH OVER THE PLAINS HEADS INTO THE EASTERN STATES FRI...A REINFORCING COLD FRONT SHOULD DIVE FROM THE FRONT RANGE OF THE ROCKIES TO THE NW GULF COAST. THE FRONT SHOULD SWEEP ACROSS THE REMAINDER OF THE AREA SAT AND SUN WITH LITTLE FANFARE ...USHERING IN A BRISK NW TO N WIND OF 20 TO 30 KT...EXCEPT TO GALE FORCE OVER THE SW GULF AND BAY OF CAMPECHE SUN. EXPECT SEAS TO BUILD UP TO 10 TO 15 FT OVER A LARGE PART OF THE GULF THIS WEEKEND...WITH WINDS AND SEAS GRADUALLY SUBSIDING MON AS HIGH PRESSURE BUILDS IN FROM THE W. CARIBBEAN SEA... A POSITIVELY-TILTED MID- TO UPPER-LEVEL TROUGH IS DIGGING INTO THE CENTRAL CARIBBEAN...WITH AN AXIS EXTENDING FROM HISPANIOLA TO N OF SAN ANDRES NICARAGUA. LIKE YESTERDAY...CLOUD-TRACKED WINDS AND WATER VAPOR IMAGERY SHOW A PLUME OF ENHANCED MID- TO UPPER-LEVEL MOISTURE SPREADING FROM ACTIVE CONVECTION IN THE E PACIFIC S OF CENTRAL AMERICA ENE TO THE NE CARIBBEAN AHEAD OF THE TROUGH. DESPITE THE ENHANCED MOISTURE...LITTLE CONVECTION IS NOTED...EXCEPT DIRECTLY UNDERNEATH THE TROUGH OVER HISPANIOLA AND IN ONE LONE STREAMER OVER THE SE CARIBBEAN. STRONGLY CONVERGENT FLOW W OF THE TROUGH AXIS HAS RESULTED IN INTENSE DRYING OVER THE NW PART OF THE AREA....WITH THE STRONGEST SUBSIDENCE COINCIDENT WITH RIDGING FROM THE SOUTHERN GULF BEGINNING TO SPILL OVER INTO THE NW PART OF THE AREA. AT THE SURFACE...LOWER HEIGHTS ALOFT HAVE TRANSLATED LOWER-THAN-NORMAL PRESSURES ACROSS THE BASIN...RESULTING FROM A DISPLACED AND FAIRLY LOW-LEVEL RIDGE NE OF THE LESSER ANTILLES. THE WEAKER-THAN-NORMAL SURFACE RIDGE HAS LED TO REDUCED TRADES THE LAST FEW DAYS...WITH TRADES TODAY EVEN WEAKER THAN YESTERDAY. HOWEVER...EARLIER MICROWAVE PASSES REVEALED E TO SE 20 KT WINDS IN THE GULF OF HONDURAS...LIKELY ENHANCED BY LOW PRESSURE COMING OUT OF THE PLAINS. OVER THE NEXT FEW DAYS...MODELS INDICATE THAT THE SHORTWAVE TROUGH CROSSING THE CENTRAL CARIBBEAN THIS EVENING SHOULD EXIT THE REGION LATER THIS WEEKEND...REPLACED BY MID- TO UPPER-LEVEL RIDGING JUST N OF THE AREA. THIS PATTERN SHOULD FAVOR A REINVIGORATED SURFACE RIDGE OVER THE SW ATLC...WHICH SHOULD HELP TRADES INCREASE SLIGHTLY...PERHAPS AT OR JUST BELOW CLIMATOLOGICAL AVERAGES. HOWEVER...THE PATTERN LOOKS TO BE A DRY ONE...WITH NO SPECIFIC AREAS OF ORGANIZED CONVECTION LIKELY EXCEPT FOR THE DIURNALLY-DRIVEN VARIETY OVER SOME OF THE MAJOR LANDMASSES NEAR PEAK HEATING. ATLANTIC OCEAN W OF 40W... THE WEAK POSITIVELY-TILTED SHORTWAVE TROUGH FROM THE CENTRAL CARIBBEAN EXTENDS NE INTO THE CENTRAL ATLANTIC TO NEAR 30N52... PER WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS. THIS FEATURE IS CARRYING A WEAK YET COMPLEX FRONTAL SYSTEM N OF 25N BETWEEN ABOUT 45W AND 65W. MORE SPECIFICALLY...THE MAIN FRONTAL WAVE... 1010 MB...IS LOCATED NEAR 30N46W... WITH AN ILL-DEFINED BOUNDARY EXTENDING WESTWARD TO A SECOND AND POORLY ORGANIZED SURFACE LOW NEAR 29N57W. THE FRONT CONTINUES SW FROM THE LOW TO NEAR 24N71W ...WHERE IT BECOMES STATIONARY. SATELLITE IMAGERY INDICATES SCATTERED TO WIDESPREAD LOW- TO MID-LEVEL CLOUDS ALONG AND DIRECTLY AHEAD OF THE FRONT...WITH ISOLATED SHOWERS AND PERHAPS A TSTM OR TWO POPPING UP WITHIN 90 NM SE OF FRONT BETWEEN 54W AND 65W. A TIGHT COMMA-SHAPED LEAF IS FORMING IN ASSOCIATION WITH THE MAIN SURFACE LOW...WITH A SOLID COVERAGE OF OVERRUNNING RAINS N OF 30N BETWEEN 40W AND 45W. A WEAK PRESSURE GRADIENT SUPPORTS NO MORE THAN 10- TO 15-KT OF WINDS ACROSS THE AREA...EXCEPT FOR AROUND 20 KT JUST N OF THE SURFACE WAVE NEAR THE WESTERNMOST SURFACE...WITH NEAR 25 KT WIND IMMEDIATELY NE OF THE STRONGER WAVE. MODELS SHOW W ATLANTIC SHORTWAVE COMBINING WITH A MORE PORTENT NORTHERN STREAM FEATURE THIS WEEKEND...WITH THE CONSOLIDATED SYSTEM RACING E OF THE AREA BY SUN. SURFACE HIGH PRESSURE SHOULD BUILD IN ITS WAKE AND GRADUALLY MIGRATE FROM W TO E...AS A STRONG COLD FRONT MAKES ITS WAY OFF THE SE U.S. COAST SUN. ATLANTIC OCEAN E OF 40W... BROAD...DEEP-LAYERED CYCLONIC FLOW CONTINUES OVER THE NE ATLANTIC...GENERALLY N OF 20N E OF 60W. THIS PATTERN SHOULD CONTINUE INTO THE WEEKEND...AS ONE SYSTEM CURRENTLY MOVING INLAND OVER NW AFRICA AND THE MEDITERRANEAN IS REPLACED BY THE SYSTEM CURRENTLY OVER THE CENTRAL ATLANTIC. WITH NO SUBTROPICAL RIDGE...TRADES HAVE COLLAPSED ACROSS MUCH OF THIS AREA AND ARE WEAKER-THAN-NORMAL STILL S OF 20 AND E OF 60W. NO IMPORTANT CHANGES ARE EXPECTED OVER THE NEXT FEW DAYS...GIVEN THAT THE PATTERN IS LIKELY TO REINFORCED. OTHERWISE...AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM W AFRICA TO JUST E OF THE LESSER ANTILLES...WITH AN AXIS RUNNING FROM 20N06W TO 12N53W. ALTHOUGH CONVECTION HAS DECREASED OVER THE TROPICAL ATLANTIC THE LAST FEW DAYS...THERE ARE TWO AREAS OF INTEREST WHICH HAVE EMERGED OVER THE LAST 24 HOURS. THE FIRST IS A CONVECTIVE CLUSTER N OF THE ITCZ...WITH WHAT APPEARS TO BE A MID-LEVEL CYCLONIC CIRCULATION CENTERED NEAR 5N18W MOVING W AT 15 TO 20 KT. THIS FEATURE COULD BE CONSIDERED ONE OF THE SEASONS FIRST AFRICAN EASTERLY WAVES. THE SECOND FEATURE IS ALONG ELONGATED SURFACE TROUGH OF NORTHEASTERLIES CONVERGING WITH EASTERLIES BETWEEN 8N AND 10N BETWEEN 45W AND 50W. EARLIER VISIBLE SATELLITE IMAGERY REVEALED A TIGHTLY-COILED LOW- TO PERHAPS MID-LEVEL CIRCULATION IN THE ASSOCIATED CONVECTION NEAR 9N46W....THOUGH THE CONVECTION SINCE THAT TIME HAS COLLAPSED. $$ KIMBERLAIN