000 AXNT20 KNHC 120000 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT FRI APR 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2345 UTC. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 5N8W 2N20W CROSSING THE EQUATOR NEAR 34W THEN TO NE BRAZIL NEAR 2S44W. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS BETWEEN 8W-11W. ISOLATED CLUSTERS OF MODERATE CONVECTION ARE WITHIN 60 NM N OF THE AXIS BETWEEN 23W AND 30W. SCATTERED MODERATE ALSO BETWEEN 1N AND 4N BETWEEN 40W AND 50W.6W ...DISCUSSION... GULF OF MEXICO... AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDING FROM S FLORIDA TO THE BAY OF CAMPECHE IS PRODUCING MODERATELY STRONG SUBSIDENCE AND FAIR SKIES OVER MUCH OF THE SOUTHERN AND EASTERN GULF THIS EVENING. WEAK SURFACE RIDGING NOSES INTO THE EASTERN GULF AND IS PRODUCING E TO SE WINDS OF 10 TO 15 KT...EXCEPT 5 TO 10 KT OVER THE FAR NE. HOWEVER...A BROAD MID- TO UPPER-LEVEL TROUGH OVER THE CENTRAL U.S. IS BEGINNING TO DIG INTO THE EASTERN STATES... DRIVING AN ASSOCIATED COLD FRONT INTO THE NW GULF FROM 30N93W TO 26N95W TO 23N98W AND THEN WINDING INLAND OVER NE MEXICO. SATELLITE AND RADAR IMAGERY INDICATE THE FRONT IS PUSHING SE WITH LITTLE FANFARE...ONLY DEFINED BY SCATTERED LOW CLOUDS BOTH BEHIND AND AHEAD OF THE BOUNDARY. W OF THE FRONT...N TO NE WINDS OF 10 TO 15 KT IS DEVELOPING AS WEAK HIGH PRESSURES BUBBLES SOUTHWARD INTO NE MEXICO...WITH TEMPERATURES 5 TO 10 DEGREES COOLER AND DEWPOINT TEMPERATURES 20 TO 30 DEGREES LOWER. IN THE SHORT-TERM...A VIGOROUS SHORTWAVE SLIDING EASTWARD IN THE BASE OF THE CENTRAL U.S. TROUGH SHOULD HELP PUSH THE FRONT THROUGH THE REMAINDER OF THE GULF SAT AND SUN...ACCOMPANIED BY BRISK NW TO N WINDS OF 20 TO 30 KT...EXCEPT TO GALE FORCE BRIEFLY OVER THE SW GULF SUN. SEAS SHOULD QUICKLY BUILD TO 8 TO 15 FT OVER THE W GULF AND 5 TO 9 FT OVER THE EASTERN GULF...WITH WINDS AND SEAS GRADUALLY SUBSIDING LATER ON MON. CARIBBEAN SEA... WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS SHOW A POSITIVELY- TILTED MID- TO UPPER-LEVEL TROUGH PUSHING SE THROUGH THE CARIBBEAN...LYING FROM 19N63 TO AROUND 12N77W. A PLUME OF UPPER TROPOSPHERIC MOISTURE BEING DRAWN NE AHEAD OF IT IS NOW CONFINED TO FARTHER NORTHERN SOUTH AMERICA THROUGH THE WINDWARD ISLANDS ...WHILE MODERATE TO STRONG SUBSIDENCE IS EVIDENT OVER THE REST OF THE CARIBBEAN COINCIDENT WITH THE CONVERGENT REGION W OF THE TROUGH AXIS AND THE STRONG MID- TO UPPER-LEVEL HIGH SPILLING FROM THE GULF INTO THE NW CARIBBEAN. WITH LARGE-SCALE SUBSIDENCE NOW OVERSPREADING MOST OF THE BASIN...VERY LITTLE IN THE WAY OF CONVECTION IS NOTED EXCEPT FROM COSTA RICA TO NORTHERN COLOMBIA AND OVER THE HIGHEST TERRAIN OF GUATEMALA AND HONDURAS. AT THE SURFACE...LOWER HEIGHTS ALOFT HAVE RESULTED IN A DISPLACED AND FAIRLY WEAK SURFACE RIDGE...WHICH IN TURN HAS TRANSLATED INTO LOWER-THAN-NORMAL SURFACE PRESSURES OVER THE ENTIRE AREA. CONSEQUENTLY...TRADES CONTINUE TO BE RATHER WEAK AS THEY HAVE BEEN THE LAST FEW DAYS...EXCEPT TYPICALLY HIGHER IMMEDIATELY NW OF THE COLOMBIAN COAST AND OVER THE GULF OF HONDURAS. IN FACT...LIKE YESTERDAY...QUIKSCAT AND ASCAT PASSES REVEAL E TO SE WINDS OF 20 TO POSSIBLY 25 KT. OVER THE NEXT FEW DAYS...THE DEEP TROUGH OVER THE CENTRAL U.S. SHOULD BARREL EASTWARD...CAUSING HEIGHTS TO COLLAPSE INTO THE WESTERN CARIBBEAN. THIS SHOULD ALLOW THE COLD FRONT SLIDING THROUGH THE GULF THIS WEEKEND TO DROP AS FAR SOUTH AS AN EASTERN CUBA-CAPE GRACIAS A DIOS NICARAGUA LINE BY EARLY TUE. FOLLOWING ITS PASSAGE...NW TO N WINDS OF 15 TO 20 KT SHOULD PUSH SOUTHWARD FROM THE YUCATAN CHANNEL IN TO THE GULF OF HONDURAS...WITH SEAS BUILDING TO 6 TO 9 FT. WITH THE MAIN DYNAMICS WELL TO THE N...ONLY SCATTERED SHOWERS AND PERHAPS AN ISOLATED TSTM COULD OCCUR NEAR OR DIRECTLY AHEAD OF THE BOUNDARY. OTHERWISE...WITH HIGH PRESSURE DISPLACED TO THE NE...LOWER-THAN-NORMAL PRESSURES AND A WEAK GRADIENT SHOULD KEEP TRADES AT OR BELOW CLIMATOLOGICAL AVERAGES STRAIGHT THROUGH EARLY NEXT WEEK. ATLANTIC OCEAN... THE WEAK POSITIVELY-TILTED SHORTWAVE TROUGH OVER THE CARIBBEAN EXTENDS WELL TO THE NE...FROM THE NE CARIBBEAN TO AROUND 31N41W PER WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS. THIS FEATURE IS CARRYING A WEAK YET COMPLEX FRONTAL SYSTEM N OF 25N BETWEEN 37W AND 60W. MORE SPECIFICALLY...THE MAIN FRONTAL WAVE LIES N OF THE AREA NEAR 33N41W...WITH AN ILL-DEFINED BOUNDARY EXTENDING SW FROM 31N40W TO 27N46W THEN WESTWARD TO A SECOND BUT WEAKER FRONTAL WAVE NEAR 27N56W. THE FRONT THEN CONTINUES SW TO NEAR 23N62W. SATELLITE IMAGERY INDICATES A BROAD AREA OF MULTI-LAYERED CLOUDINESS...WITH A FEW EMBEDDED SHOWERS AND TSTMS IN THE DIVERGENT REGION AHEAD OF THE TROUGH AXIS. MOST OF THE ACTIVITY IS LIMITED TO THE AREA N OF 20N W OF 50W...WITH THE GREATEST CONCENTRATION WITHIN 350 NM E OF THE ASSOCIATED FRONT N OF 27N. ALTHOUGH FAIRLY LIGHT WINDS COVER MUCH OF THE CENTRAL AND WESTERN ATLANTIC...LOCALLY STRONGER SOUTHERLY WINDS OF 20 TO 30 KT ARE NOTED N OF 26 E OF THE FRONT. MODELS SHOW THIS FEATURE IN THE PROCESS OF MERGING WITH A MORE POTENT NORTHERN STREAM SYSTEM TONIGHT AND SAT...WITH THE CONSOLIDATED SYSTEM RACING E OF THE AREA BY SUN. A RECONSTITUTED SURFACE RIDGE IN ITS WAKE SHOULD MIGRATE FROM THE WESTERN TO THE CENTRAL ATLANTIC..AS A STRONG COLD FRONT MOVES OFF THE SE U.S. COAST SUN. ELSEWHERE...A WEAK 1026 MB SURFACE RIDGE NEAR 37N26W CURRENTLY EXTENDS INTO THE NE ATLANTIC BUT SHOULD QUICKLY REPLACED WITH A DEEP-LAYERED CYCLONIC FLOW THIS WEEKEND...INTRODUCED AFTER THE PASSAGE OF THE ABOVE FRONTAL SYSTEM. A PATTERN OF DEEP-LAYERED CYCLONIC FLOW HAS PERSISTED OVER THE EAST ATLANTIC N OF 15N E OF 60W FOR MUCH OF THE WEEK...WHICH HAS CONTINUED TO KEEP THE STRENGTH OF THE TRADE WIND FLOW BELOW AVERAGE. WEAKER-THAN- NORMAL TRADES AND LOWER-THAN-NORMAL SURFACE PRESSURES SHOULD PREVAIL ACROSS THIS AREA THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK. OTHERWISE...AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM NW AFRICA TO JUST E OF THE LESSER ANTILLES...WITH AN AXIS RUNNING FROM 20N07W TO 12N58W. S OF THE RIDGE AXIS...CONVECTION REMAINS FAIRLY LIMITED...WHICH IS IN STARK CONTRAST TO THAT OBSERVED LAST WEEK INTO EARLY THIS WEEK. REAL-TIME NCEP RE-ANALYSIS DATA INDICATE THAT THE RECENT INCREASE IN CONVECTIVE ACTIVITY WAS LIKELY RELATED TO A FAST-MOVING TROPICAL CONVECTIVE FORCING...WHICH HAS NOW MOVED E AFRICA AND THE INDIAN OCEAN. $$ KIMBERLAIN/ECKERT