000 AXNT20 KNHC 051058 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SAT APR 05 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 7N11W 6N17W 2N22W CROSSING THE EQUATOR AT 31W TO 5S37W. SCATTERED TO WIDESPREAD STRONG CONVECTION WITHIN 300 NM EITHER SIDE OF AXIS BETWEEN 22W AND 31W. ISOLATED MODERATE FROM 3S TO 5N BETWEEN 40W AND 48W. ...DISCUSSION... GULF OF MEXICO... A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE ARKLATEX REGION IS DRAGGING A WEAK COLD FRONT INTO THE NW GULF OF MEXICO AND FAR NE MEXICO. ALTHOUGH A QUIKSCAT PASS FROM YESTERDAY EVENING REVEALED N TO NE 20- TO 25-KT WINDS BEHIND THE FRONT... MUCH OF THE DATA APPEARED TO BE RAIN-CONTAMINATED AND THUS NOT CONSIDERED RELIABLE. HOWEVER...A COMBINATION OF COASTAL...CMAN ...AND BUOY OBSERVATIONS DO CONFIRM N TO NE WINDS IN THAT RANGE DIRECTLY BEHIND THE FRONT...WITH SEAS BUILDING TO 5 TO 7 FT...AND A SOLID DECK OF STRATUS CLOUDS EXTENDING BACK ALMOST 150 NM. RADAR AND SATELLITE IMAGERY SHOW SCATTERED TO LOCALLY NUMEROUS TSTMS WITHIN 30 TO 60 NM E OF THE FRONT FROM THE SE LA COAST NE INTO THE WESTERN FL PANHANDLE. A CLOSER INSPECTION OF THESE OBSERVATIONS REVEALS A WELL-DEFINED OUTFLOW BOUNDARY PROPAGATING SE FROM THIS NASCENT CONVECTIVE LINE...WHILE INDIVIDUAL CELLS CONTINUE MOVING NE AT 30 TO 40 KT. IN ADDITION...SEVERAL OBSERVATIONS ALSO SUGGEST A WEAK 1007 MB SFC LOW IN ITS FORMATIVE STAGES ALONG THE FRONT ANALYZED CLOSE TO 30N91W ...MOVING NE AT 20 TO 25 KT. ELSEWHERE SE OF THE FRONT... SE TO S WINDS OF 15 TO 20 KT COVER THE GULF...WITH SKIES REMAIN MOSTLY CLOUD FREE EXCEPT FOR SOME ISOLATED CONVECTIVE CELLS SPROUTING UP FROM 26N TO 27N BETWEEN 90W AND 92W AND AHEAD OF THE WITHIN ABOUT 60 NM SE OF THE SE TIP OF LA. SHORT-TERM MODEL GUIDANCE SHOWS THE ARKLATEX SHORTWAVE BEGINNING TO LIFT OUT OVER THE SE U.S. LATE SAT...UNABLE TO DIG MUCH FURTHER THANKS TO A FAIRLY SOLID MID-LEVEL RIDGE OVER THE WESTERN ATLANTIC. DESPITE THIS...A BROAD PATTERN OF UPPER-LEVEL DIVERGENCE...WARM AIR ADVECTION...AND POSITIVE VORTICITY ADVECTION AHEAD OF THE SYSTEM SHOULD RESULT IN FAIRLY WIDESPREAD CONVECTIVE RAINS NOT ONLY ACROSS THE INTERIOR SE BUT ALSO ALONG THE N CENTRAL AND NE GULF COAST TODAY. HOWEVER...WITH THE UPPER SUPPORT ALREADY PUSHING NE AND THE MID- TO UPPER-LEVEL BECOMING NEARLY PARALLEL ALONG THE FRONT...EXPECT THE FRONT TO STALL NEARLY HALFWAY ACROSS THE GULF WITH A NE-SW ORIENTATION. WHAT IS LEFT OF THE FRONT SHOULD RETREAT AS A WARM FRONT SUN INTO MON...LYING CLOSE TO OR JUST INLAND FROM THE GULF COAST. CARIBBEAN SEA... WATER VAPOR IMAGERY REVEALS HIGH-LEVEL WESTERLY FLOW DOMINATING MUCH OF THE BASIN...WITH A WEAKENING MID- TO UPPER-LEVEL TROUGH EXTENDING FROM 21N79W INTO THE E PACIFIC W OF COSTA RICA. MODERATE TO STRONG SUBSIDENCE ASSOCIATED WITH A LARGE MID- TO UPPER-LEVEL ANTICYCLONE IN THE TROPICAL E PACIFIC IS OBSERVED AS FAR E AS THE WESTERN CARIBBEAN W OF THE TROUGH AXIS. HOWEVER...A PLUME OF MOISTURE WITH ORIGINS FROM THE AMAZON IS BEING DRAWN NORTHWARD OVER THE CENTRAL CARIBBEAN E OF THE TROUGH AXIS. THIS SUBTLE INCREASE IN UPPER TROPOSPHERIC MOISTURE AND THE DIFFLUENT UPPER-LEVEL FLOW HAS HELPED IGNITE SOME CONVECTION LATE YESTERDAY...ALTHOUGH WHAT FORMED WAS PRETTY SCARCE. IN FACT... ONLY SPORADIC CONVECTIVE ELEMENTS WERE NOTED FROM PANAMA THROUGH NORTHERN COLOMBIA...WITH UNRELATED LATE AFTERNOON CONVECTION... OVER CUBA...LIKELY A RESULT OF LOCAL SEA BREEZE CIRCULATIONS. AT THIS HOUR...WHAT REMAINS IS SOME ISOLATED CONVECTIVE CELLS IMMEDIATELY SE OF THE SE NICARAGUAN COAST. OTHERWISE...STRONG SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC HAS AN EXTENSION INTO THE CARIBBEAN SEA AND IS PROVIDING FRESH TRADES ACROSS THE EASTERN AND PARTS OF THE CENTRAL PART OF THE AREA. HOWEVER...REAL-TIME NCEP RE-ANALYSIS DATA INDICATES THAT CURRENT TRADES ARE FAIRLY CHARACTERISTIC OF THIS TIME OF THE YEAR...EXCEPT PERHAPS SLIGHTLY STRONGER- THAN-NORMAL OVER THE FAR E. OVER THE NEXT FEW DAYS...A WELL-DEFINED MID- TO UPPER-LEVEL RIDGE SHOULD SET UP SHOP N OF THE CARIBBEAN...IN THE VICINITY OF 25N62W...WHILE THE TROUGH CURRENTLY OVER THE WESTERN CARIBBEAN MOVES W AND LOSES ITS IDENTITY. THIS SHOULD SET UP A PATTERN OF LIGHT UPPER-LEVEL WINDS ACROSS THE AREA...WITH SUBSTANTIAL EASTERLY WIND ANOMALIES LIKELY FROM THIS WEEKEND INTO EARLY NEXT WEEK. MEANWHILE...THE STRONG SURFACE RIDGE NOW NEAR 36N54W SHOULD WEAKEN AND SHIFT SE TO 28N62W BY EARLY MON...WHICH SHOULD ALLOW TRADES TO RELAX OVER THE EASTERN AND CENTRAL CARIBBEAN. ATLANTIC OCEAN... AN ANOMALOUSLY STRONG MID-LEVEL RIDGE REMAINS LOCKED IN PLACE OVER THE WESTERN ATLANTIC NEAR 25N62W...DIRECTING THE STRONGER MID-LATITUDE FLOW OVER THE EASTERN CONUS N OF THE AREA. MUCH OF THE STRONGER MID-LATITUDE FLOW DIGS EASTWARD INTO A BROAD MID- TO UPPER-LEVEL TROUGH W OF 50W AND N OF 15N...WITH AN ASSOCIATED DEEP-LAYERED CYCLONIC CIRCULATION CLOSE TO 40N36W. W OF THE TROUGH...A LARGE DOME OF SURFACE HIGH PRESSURE IS CENTERED NEAR 34N51W AND DOMINATES MUCH OF THE ATLANTIC...IN SOME CASES WITH ENHANCED TRADES. IN FACT...EARLIER QUIKSCAT PASSES AS WELL AS THE EASTERN EDGE OF A MORE RECENT 0842 UTC REVEAL NE TO E WINDS OF 20- TO 25-KT OVER A LARGE EXPANSE S OF 20N AND E OF THE LESSER ANTILLES TO ABOUT 40W....WITH SEAS GENERALLY 9 TO 12 FT IN NE SWELL. THE ABOVE PATTERN SHOULD CONTINUE INTO THE WEEKEND...WITH THE TRADES GRADUALLY DIMINISHING TO CLIMATOLOGICAL LEVELS AND SEA SUBSIDING TO 7 TO 10 FT BY LATE SUN. W OF 50W...A BROAD SURFACE CYCLONIC FLOW COVERS THE AREA N OF 25N...WITH A SURFACE COLD FRONT LOCATED FROM 31N31W TO 26N44W TO THE BEGINNING A WARM FRONT STARTING AT 31N56W. THE FRONT IS MARKED BY THE LEADING EDGE OF A FAIRLY DENSE STRATOCUMULUS DECK OF CLOUDS...THOUGH THERE IS LITTLE ELSE ALONG THE IMMEDIATE FRONT. AS THE FRONT RACES SE TODAY...THE INJECTION OF COOLER AIR SHOULD BRIEFLY RE-INVIGORATE THE LARGE CYCLONIC CENTER NEAR THE SE AZORES...WHICH SHOULD REINFORCE THE CYCLONIC FLOW OVER THE NE PART OF THE AREA. ELSEWHERE...WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS INDICATE A NARROW RIDGE S OF ABOUT 12N FROM THE NW COAST OF AFRICA TO JUST SE OF THE ANTILLES. THE DEEP EASTERLIES S OF THE RIDGE AXIS ALONG WITH THE PRESENCE OF A KELVIN WAVE APPROACHING 10W HAVE BEEN PROVIDING A FAVORABLE ENVIRONMENT FOR ENHANCED CONVECTION ALONG THE ITCZ THE LAST FEW DAYS. THIS PATTERN OF ANOMALOUS EASTERLY FLOW AND ENHANCED CONVECTION SHOULD CONTINUE THROUGH EARLY THIS WEEKEND BEFORE DIMINISHING AS THE KELVIN WAVE PROPAGATES E OF THE AREA. $$ KIMBERLAIN