000 AXNT20 KNHC 211748 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI MAR 21 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 3N17W CROSSING THE EQUATOR AT 27W THEN TO 3S41W. SCATTERED MODERATE CONVECTION WAS OCCURRING THIS MORNING WITHIN 150 NM EITHER SIDE OF A LINE EXTENDING FROM 4N29W TO 3S7E. ...DISCUSSION... GULF OF MEXICO... A RELATIVELY FLAT...MID- TO UPPER-LEVEL TROUGH OVER THE WRN ATLANTIC HAS DRAGGED AN ASSOCIATED COLD FRONT TO A POSITION FROM THE STRAITS OF FLORIDA TO THE NE TIP OF THE YUCATAN. THE FRONT LINKS UP WITH A WEAK 1016MB SURFACE LOW MIDWAY BETWEEN MERIDA AND COZUMEL AND THEN CONTINUES SWD TO NEAR 14.5N88.5W. WITH LITTLE AMPLITUDE TO THE WRN ATLANTIC TROUGH AND A REASONABLY STRONG MID-LEVEL RIDGE HOLDING SWAY OVER THE NORTHERN CARIBBEAN ...THE FRONT HAS PREDICTABLY BECOME STATIONARY. MULTI-CHANNEL MICROWAVE IMAGERY INDICATES PRECIPITABLE WATER VALUES OF 1.5 TO 1.75 INCHES NEAR...REFLECTING A MOISTURE-RICH AIR MASS WHICH IS ASCENDING THE BOUNDARY. THE OVERRUNNING PATTERN IS RESULTING IN SCATTERED TO OCCASIONALLY BROKEN LOW- TO MID-LEVEL CLOUDS COVERING MUCH OF THE SERN AND S CENTRAL GULF OF MEXICO...WITH DENSE LOW CLOUDS ALSO COVERING MUCH OF THE YUCATAN AND THE HIGHER TERRAIN OF CENTRAL AMERICA. OTHER THAN THE LOW- TO MID-LEVEL CLOUDS...FORCING MECHANISMS REMAIN FAIRLY WEAK AND THUS THE ONLY CONVECTION TO SPEAK OF IS SPROUTING EARLY WITHIN ABOUT 60 NM S OF 23N BETWEEN 85W AND 87W EARLY THIS AFTERNOON. ELSEWHERE...A SHALLOW STRATOCUMULUS DECK OF CLOUDS IS VEILED ACROSS THE NW AND N CENTRAL GULF BUT CLEAR SKIES COVER THE NE AND SW GULF UNDER THE INFLUENCE OF WEAK HIGH PRESSURE. A MORNING QUIKSCAT PASS REVEALS A GENERALLY LIGHT WIND REGIME NORTH OF THE FRONT...WITH WINDS N TO NE WINDS OF 10 TO 15 KT EXCEPT 20 TO OCCASIONALLY 25 KT E OF 90W WHERE THE PRESSURE GRADIENT IS STRONGER. BUOY...CMAN...AND SHIP REPORTS INDICATE 5 TO 8 FT SEAS IN N E SWELL COVERING THE SOUTHER HALF OF THE GULF...WHILE 2 TO 5 FT SEAS ARE THE RULE N OF ABOUT 26N. MODEL GUIDANCE DEPICTS AN ILL-DEFINED...SRN STREAM SHORTWAVE RACING ACROSS THE GULF LATE TONIGHT AND SAT..WHICH SHOULD LEAD TO A GENERAL RETREAT OF THE STATIONARY FRONT ACROSS THE EXTREME SERN GULF AND FL. AS THIS OCCURS...A WEAK SURFACE WAVE IS FORECAST TO FORM ALONG THE FRONT AND REACH THE W COAST OF FL SAT AFTERNOON. AS THE SURFACE WAVE DARTS NE INTO THE WRN ATLANTIC SAT NIGHT...EXPECT THE BOUNDARY TO RETURN ACROSS FL AND THE GULF EARLY SUN...FOLLOWED BY A SECOND REINFORCING SHOT OF COOLER AND DRIER AIR SUN. CARIBBEAN SEA... A STRONG MID- TO UPPER-LEVEL LIES DIRECTLY N HISPANIOLA AND PUERTO RICO AND SHOULD PREVAIL ACROSS THE CARIBBEAN BASIN THROUGH AT LEAST EARLY THIS WEEKEND. THE RIDGE...WHICH HAS DOMINATED THE REGION FOR MUCH OF THIS WEEK...CONTINUES TO FAVOR BROAD SUBSIDENCE AND A LACK OF CONVECTIVE CLOUDS...ESPECIALLY E OF 80W. IN FACT...WATER VAPOR IMAGERY INDICATES THE STRONGEST SUBSIDENCE IS CENTERED FROM E OF THE LESSER ANTILLES TO ABOUT 75W. HOWEVER...MODELS SUGGEST THAT THE INFLUENCE OF THIS FEATURE SHOULD DIMINISH LATER THIS WEEKEND...AS A BROAD TROUGH DIGGING OVER THE ERN CONUS REACHES DEEP INTO THE WRN CARIBBEAN. OTHERWISE...THERE IS STILL EVIDENCE OF WHAT WAS A RARE FRONTAL PASSAGE OVER THE NE CARIBBEAN AND LESSER ANTILLES EARLIER THIS WEEK...WITH PATCHY STRATOCUMULUS CLOUDS INTERSPERSED WITH DEEPER CUMULUS. THE MOST RECENT SOUNDING FROM SAN JUAN STILL REVEALS A TRADE WIND INVERSION WHICH IS ATYPICALLY HIGH AT ROUGHLY 750 MB. IN ADDITION...DEWPOINTS FROM ABOUT MARTINIQUE NWWD THROUGH PUERTO RICO REMAIN IN THE 60S...REPRESENTING A SLOW RECOVERY FROM WHAT THEY WERE JUST A FEW DAYS AGO. W OF 80W...THE STATIONARY FRONT OVER THE GULF EXTENDS SWD ALONG BUT OFFSHORE THE YUCATAN AND BELIZE COASTS...WITH AN EXTENSION INTO THE MORE MOUNTAINOUS TERRAIN OF CENTRAL AMERICA. WHERE LOW-LEVEL NWLY FLOW MEETS THE TRADES...WIDESPREAD CLOUDINESS IS NOTED NEAR AND ALONG THE FRONT OVER THE WRN GULF OF HONDURAS WITH LITTLE IN THE WAY OF ANY ORGANIZED PRECIPITATION. VISIBLE SATELLITE IMAGERY ALSO INDICATED A WEAK LOW-LEVEL CYCLONIC CIRCULATION IMMEDIATELY AHEAD OF THE FRONT OVER THE CENTRAL GULF OF HONDURAS. HOWEVER...A QUIKSCAT PASS FROM EARLIER SUGGESTED THAT THE CIRCULATION IS ABOVE THE SURFACE LAYER. FINALLY...LONG PERIOD NE SWELL CONTINUES TO ARRIVE PRIMARILY OVER THE CARIBBEAN...WITH A MIX OF BUOYS AND SHIPS INDICATING 10 TO 14 FT WAVE HEIGHTS STILL OVER THE AREA E OF 65W. ONLY A GRADUAL DIMINUTION IN WAVE HEIGHT IS EXPECTED DURING THE NEXT 24 HOURS. ATLANTIC... THE SAME COLD FRONT OVER THE GULF EXTEND NEWD THROUGH THE CENTRAL BAHAMAS ALONG A LINE RUNNING FROM 24N80W TO 26N70W TO 31N59W AS OF 1500 UTC....WITH THE FRONT STATIONARY W OF ABOUT 70W. OVERRUNNING MOISTURE ALONG THE BOUNDARY HAS CAUSED THE DEVELOPMENT OF A BAND OF SOLID...LOW- TO MID-LEVEL CLOUDS WITHIN 90 NM NORTH OF THE FRONT...POSSIBLY MIXED WITH LIGHT SHOWER ACTIVITY. HOWEVER...AS WAS THE CASE IN THE GULF...LIFT ALONG THE FRONT IS WEAKER THAN YESTERDAY...AND THERE IS NO ORGANIZED IMPULSE ALOFT TO SUSTAIN ANYTHING MORE THAN SHOWERS AND CLOUDS. E OF THE BOUNDARY...A 1022 MB LOW-LEVEL RIDGE IS CENTERED NEAR 24N65W AND IS MOVING SLOWLY E...KEEPING FAIRLY TRANQUIL CONDITIONS IN PLACE. A 1014 UTC QUIKSCAT PASS STILL INDICATED SWLY 20 TO 25 KT WITHIN ABOUT 300 NM E OF THE FRONT...MOSTLY N OF 30N. ELSEWHERE...A DEEP CLOSED CYCLONE N OF THE AREA NEAR 36N40W IS CARRYING A SLOW-MOVING COLD FRONT FROM 31N32W TO 16N52W. THIS SYSTEM IS THE SAME STORM...WHICH DEEPENED TO ABOUT 965MB LATE THIS PAST WEEKEND/EARLY THIS WEEK AND PRODUCED AN IMPRESSIVE NW TO N SWELL OVER THE WRN ATLANTIC. THIS SWELL CONTINUES TO PROPAGATE FROM ITS SOURCE REGION AND HAS NOW ENVELOPED THE BETTER PART OF THE TROPICAL ATLANTIC. IN FACT...10 TO 15 FT WAVES IN A NW SWELL COVER THE AREA S OF 31N AND E OF 60W. ALL OF THE ASSOCIATED OVERRUNNING CLOUDS AND PRECIPITATION LIE NORTH AND EAST OF THE AREA...WITH ONLY SPOTTY LOW CLOUDS IN THE FRONTS WAKE. $$ KIMBERLAIN