000 AXNT20 KNHC 082348 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE APR 08 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... THE ITCZ AXIS IS CENTERED ALONG 04N08W 3N19W CROSSING THE EQUATOR AT 29N THEN TO NE COAST OF BRAZIL NEAR 3N39W. SCATTERED MODERATE CONVECTION IS WITHIN 300 NM N OF AXIS BETWEEN 20W AND 31W. ...DISCUSSION... GULF OF MEXICO... A POSITIVELY-TITLED SHORTWAVE TROUGH EXTENDING FROM EAST CENTRAL FLORIDA TO THE GULF OF HONDURAS CONTINUES TO GRADUALLY EXIT THE EASTERN GULF THIS EVENING...LEAVING BEHIND WEAK SHORTWAVE RIDGING ALOFT FROM THE NE TO THE SW GULF. AN ASSOCIATED STATIONARY FRONT LIES ACROSS THE FLORIDA STRAITS THROUGH THE EXTREME SOUTHEASTERN GULF OF MEXICO...THOUGH THE BOUNDARY IS NOT PARTICULARLY WELL-DEFINED. WATER VAPOR INDICATES AN EMBEDDED CYCLONIC CIRCULATION ALONG THE SHORTWAVE TROUGH OVER THE FLORIDA STRAITS APPROACHING THE CENTRAL KEYS...A FEATURE WHICH MOST OF THE SHORT-TERM GUIDANCE INITIALIZES. A PATTERN OF WEAK UPPER-LEVEL DIVERGENCE AND LIFT AHEAD OF THE CIRCULATION HAS SPARKED A ROUND OF LATE AFTERNOON CONVECTION OVER THE FLORIDA STRAITS...WHILE OVERRUNNING RAINS ARE OCCURRING N OF THE BOUNDARY OVER S FLORIDA AND PARTS OF THE KEYS. W OF THE TROUGH AXIS...WATER VAPOR IMAGERY SHOWS MODERATE TO STRONG SUBSIDENCE OVERTAKING NEARLY ALL THE GULF...WITH THE STRONGEST DRYING NOTED IN THE STRONGEST UPPER-LEVEL CONVERGENCE JUST W OF THE BASE OF THE TROUGH IN THE VICINITY OF THE YUCATAN. OTHERWISE...WEAK SURFACE RIDGING BULGES SOUTHWESTWARD FROM N FLORIDA INTO THE SW GULF...KEEPING A GENERALLY LIGHT E TO SE WIND FLOW ACROSS THE REGION AND 2 TO 5 FT SEAS. MODELS SHOW A BROAD MID- TO UPPER-LEVEL RIDGE BUBBLING NORTHEASTWARD FROM SOUTHERN MEXICO THE NEXT FEW DAYS...IN RESPONSE TO A PARTICULARLY STRONG DISTURBANCE ROLLS INTO THE FAR WEST. AS THIS OCCURS...BROAD SURFACE LOW PRESSURE IS FORECAST TO FORM ACROSS THE SOUTHERN PLAINS...WHICH SHOULD RESULT IN A HEALTHY RETURN FLOW AND SEAS BUILDING TO 5 TO 8 FT OVER THE WESTERN HALF OF THE GULF JUST BEYOND MID-WEEK. WITH SURFACE HIGH PRESSURE STILL NOSING INTO THE EASTERN GULF...LIGHT WINDS AND SEAS OF 2 TO 4 FT SHOULD CONTINUE TO PREVAIL. OTHERWISE ...BROAD MID- TO UPPER-LEVEL RIDGING ACROSS THE REGION SHOULD KEEP A TRANQUIL WEATHER PATTERN ACROSS THE AREA THROUGH LATE WEEK. CARIBBEAN SEA... THE MID- TO UPPER-LEVEL SHORTWAVE EXITING THE GULF EXTENDS FROM FLORIDA THROUGH THE GULF OF HONDURAS AND SW TO AROUND 10N88W... WHILE WEAK MID- TO UPPER-LEVEL RIDGING LIES FARTHER E OVER THE EASTERN AND CENTRAL PART OF THE BASIN. RECENT WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS REVEAL A WEAK CYCLONIC CIRCULATION IN THE BASE OF THE TROUGH JUST W OF COSTA RICA. A DIFFLUENT UPPER-LEVEL FLOW...DAYTIME HEATING...AND SURFACE LOW PRESSURE AND CONVERGENCE E OF THIS FEATURE HAS LED TO SCATTERED TO LOCALLY NUMEROUS TSTMS OVER COSTA RICA... PANAMA ...AND NW COLOMBIA. A PLUME OF MOISTURE STREAKING NE FROM THE CONVECTION CONTINUES INTO THE CENTRAL AND EASTERN CARIBBEAN TO NEAR 65W...WHISKED EASTWARD BY A WEAK WESTERLY FLOW ALOFT. LATE AFTERNOON CONVECTION WAS ALSO NOTED OVER MOST OF CUBA...ENHANCED BY THE SHORTWAVE TROUGH AND EMBEDDED CYCLONIC CIRCULATION MOVING THROUGH THE AREA...NOT TO MENTION LOCAL SEA BREEZE CIRCULATIONS. OTHERWISE...WEAK SURFACE RIDGING NE OF THE AREA HAS AN EXTENSION INTO THE CARIBBEAN SEA...WHICH IS KEEPING TRADES AT OR JUST BELOW CLIMATOLOGICAL LEVELS. SEAS RANGE FROM 4 TO 7 FT OVER MOST OF THE REGION...EXCEPT 1 TO 3 FT NEAR THE CUBAN COAST AND 6 TO 9 FT NW OF THE COLOMBIA COAST. AS THE SHORTWAVE TROUGH CURRENTLY MOVING INTO THE SW ATLANTIC DIGS INTO THE NORTHERN CARIBBEAN THE NEXT FEW DAYS...EXPECT THE SURFACE RIDGE NE OF THE AREA TO WEAKEN FURTHER ALONG WITH THE TRADES. A DIFFLUENT UPPER-LEVEL FLOW MAINLY N OF 15N AND E OF HISPANIOLA COULD RESULT IN A NOMINAL INCREASE IN RAIN CHANCES ACROSS THESE AREAS...PARTICULARLY AROUND PEAK HEATING. ATLANTIC OCEAN... THE SHORTWAVE TROUGH DEPARTING THE EASTERN GULF THIS EVENING EXTENDS FROM 31N77W THROUGH THE E CENTRAL FLORIDA COAST AND INTO THE FLORIDA STRAITS. AN ASSOCIATED...WEAK FRONTAL BOUNDARY LIES FROM 31N72W TO A 1013 MB SURFACE WAVE NEAR 29N75W...WITH THE FRONT CONTINUING SW ACROSS THE WESTERN BAHAMAS AND ULTIMATELY INTO THE STRAITS OF FLORIDA. LATE AFTERNOON VISIBLE IMAGERY REVEALS A BROAD CYCLONIC ENVELOPE NEAR THE MAIN SURFACE WAVE ALONG THE FRONT...WITH SEVERAL DISTINCT LOW-LEVEL SWIRLS ATTEMPTING TO ROTATE AROUND EACH OTHER. WITH FEW SURFACE OBSERVATIONS ACROSS THIS REGION AND NO RECENT MICROWAVE PASSES...DETERMINING THE EXACT FRONTAL LOCATION HAS PROVEN RATHER DIFFICULT. FARTHER W...WATER VAPOR IMAGERY REVEALS A COMMA HEAD OF HIGHER MOISTURE CROSSING THE FLORIDA STRAITS LATE THIS AFTERNOON...WHICH SEEMS TO BE A DISTINCT AND TIGHT MID- TO UPPER-LEVEL CIRCULATION NEAR 24.5N80W...MOVING NE AT 10 TO 15 KT. AS NOTED PREVIOUSLY...UPPER-LEVEL DIVERGENCE AND LIFT AHEAD OF THIS FEATURE HAS RESULTED IN SPOTTY CONVECTION FROM THE FLORIDA STRAITS...WHICH IS NOW BEGINNING TO MOVE INTO THE SW BAHAMAS. N OF THE BOUNDARY IN THE COLD SECTOR...OVERRUNNING LATE AFTERNOON RAINS HAVE DEVELOPED ACROSS THE SOUTHERN FLORIDA PENINSULA AND ARE SPREADING NE INTO THE E FL COASTAL WATERS. FINALLY...W OF THE BOUNDARY...WEAK SURFACE RIDGING ALONG THE SE U.S. COAST EXTENDS INTO THE FLORIDA PENINSULA...WHICH HAS HELPED KEEP NE 15 TO 20 KT WINDS AND 7 TO 10 FT SEAS ACTIVE FROM N OF THE BAHAMAS TO THE NE FLORIDA COAST. AS MID- TO UPPER-LEVEL RIDGING BUILDS ACROSS THE GULF THE NEXT FEW DAYS...MODELS DIG THE SHORTWAVE CURRENTLY ACROSS FLORIDA AND THE SW ATLANTIC DOWN THE E SIDE OF THE RIDGE INTO THE WESTERN ATLANTIC AND THE NORTHERN CARIBBEAN. THIS SHOULD HELP DRIVE THE STATIONARY FRONT SE OF FLORIDA DEEPER INTO THE WESTERN ATLANTIC ...WHILE WEAK LOW PRESSURE MOVES NE ALONG THE FRONT TO NEAR 29N56W BY EARLY FRI. WHILE SCATTERED SHOWERS AND TSTMS ERUPT ALONG THE BOUNDARY...ESPECIALLY NEAR THE MAIN SURFACE WAVE...HIGH PRESSURE SHOULD CONTINUE BUILDING SW BEHIND THE BOUNDARY...MAINTAINING LIGHT NE TO E WINDS ACROSS THE SW ATLANTIC. ELSEWHERE...A BROAD CYCLONIC CIRCULATION AT MID- AND UPPER- LEVELS DOMINATES THE AREA N OF 15N AND E OF 60W....WITH THE TAIL OF AN ASSOCIATED COLD FRONT STILL TO 22N39W. THIS PATTERN HAS RESULTED IN A DISTINCT BREAK IN THE ATLANTIC SUBTROPICAL RIDGE ...WITH THE RESULT BEING WEAKER-THAN-NORMAL TRADES ACROSS THE TROPICAL AND SUBTROPICAL ATLANTIC. IN FACT...LATEST REAL-TIME NCEP RE-ANALYSIS DATA SUGGESTS WESTERLY WIND ANOMALIES OF 5 TO 10 KT S OF 20N AND E OF 60W...WITH MUCH LARGER ANOMALIES OF 15 TO 30 KT N OF 20N W OF 60W. NO IMPORTANT CHANGES TO THIS PATTERN ARE EXPECTED THE NEXT FEW DAYS. FINALLY...A NARROW MID- TO UPPER-LEVEL RIDGE LIES S OF 12N OVER THE TROPICAL ATLANTIC WITH A RIDGE AXIS GENERALLY ALONG 8N. DEEP EASTERLIES ARE PRESENT S OF THE AXIS...WITH REAL-TIME NCEP RE-ANALYSIS DATA INDICATING EASTERLY WIND ANOMALIES OF UP TO 20 KT. OTHERWISE...SPORADIC BUT ENHANCED CONVECTION CONTINUES FROM THE GULF OF GUINEA TO EITHER SIDE OF THE EQUATOR AS FAR W AS 30W. SATELLITE IMAGERY REVEALS A WELL-DEFINED MID-LEVEL CYCLONIC CIRCULATION EMBEDDED WITHIN THE DYING CONVECTION CENTERED CLOSE TO 5N21W...WITH ANOTHER ONE CLOSE TO 9N35W. THOUGH ENHANCED... THE CONVECTION IS SUBSTANTIALLY LESS THAN WHAT WAS OCCURRING LATE LAST WEEK INTO THIS PAST WEEKEND...WHEN AN ATMOSPHERIC DISTURBANCE KNOWN AS KELVIN WAVE WAS MOVING THROUGH THE REGION. $$ KIMBERLAIN