000 AXNT20 KNHC 251042 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SAT AUG 25 2007 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 1015 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 24W/25W S OF 20N MOVING W 10-15 KT. AFTER MOVING SLUGGISHLY WWD OVER THE PAST DAY OR SO IT LOOKS LIKE THE SYSTEM HAS PICKED UP SPEED...WHICH MAKES SENSE GIVEN THE INCREASED 600-850 MB ELY JET INIDCATED IN THE NEARBY SOUNDINGS. EARLY VIS IMAGES SHOW BROAD TURNING IN THE STRATOCUMULUS CLOUDS SUGGESTING THE AXIS COULD BE CLOSER TO 26W. A 7Z QSCAT PASS AND DATA FROM THE CAPE VERDE ISLANDS INDICATE LITTLE ASSOCIATION AT THE SFC BUT...THE LOW TO MID LEVEL CLOUD DRIFT WINDS SHOW THE BROAD GYRE STRUCTURE MENTIONED ABOVE. SCATTERED SHOWERS AND TSTMS ARE LINEAR IN SHAPE EMBEDDED IN THE ITCZ FROM 11N-13N E OF 25W. TROPICAL WAVE IS ALONG 50W S OF 14N MOVING W 10 KT. THIS SYSTEM APPEARS TO HAVE BECOME A LITTLE BETTER ORGANIZED WITH LOW LEVEL TURNING CLEARLY APPARENT ON VIS IMAGES...THOUGH STILL WELL EMBEDDED IN THE ITCZ. SCATTERED SHOWERS AND TSTMS ARE CONFINED TO THE INTERSECTION OF THE ITCZ FROM 8N-11N WITHIN 180 NM EITHER SIDE OF THE WAVE AXIS. A SIDE NOTE...IT'S DIFFICULT TO DECIPHER IF THIS IS A TROPICAL WAVE (ORIGINATING FROM AFRICA) OR A DISTURBANCE WITHIN THE ITCZ. A HIGHER AMPLITUDE WAVE LIKE FEATURE APPEARS TO BE APPROACHING THE LESSER ANTILLES. FOR NOW ANALYZED THE NRN PART OF THAT FEATURE AS A TROUGH BUT DAY SHIFT MAY MAKE SOME ADJUSTMENTS. TROPICAL WAVE IS IN THE W CARIBBEAN ALONG 81W S OF 18N MOVING W 15-20 KT OVER THE PAST 24 HRS. IR IMAGES SHOWS A BIT OF CURVATURE TO THE SHOWER/TSTM ACTIVITY NEAR THE BASE OF THE WAVE EMBEDDED WITHIN THE ITCZ S OF 11N BETWEEN 77W-83W. OTHERWISE...LITTLE SIGNATURE OR SHOWER ACTIVITY IS APPARENT IN THE AVAILABLE DATA ACROSS THE REMAINDER OF THE AXIS. THE NRN PORTION OF A HIGH AMPLITUDE TROPICAL WAVE EXTENDS INTO THE S GULF ALONG 89W S OF 24N MOVING W 10-15 KT. LOW-LEVEL LIFT ASSOCIATED WITH THIS WAVE AND DIFFLUENCE ALOFT IS GENERATING SCATTERED TSTM ACTIVITY OVER S MEXICO AND THE BAY OF CAMPECHE. AN AREA OF LOW PRES HAS FORMED NEAR THE SRN EXTENSION OF THE WAVE IN THE GULF OF TEHUANTEPEC...SEE THE EPAC TWD FOR DETAILS. EARLIER SHIP/BUOY DATA DID INDICATE SOME SFC TURNING AND SLIGHTLY LOWER PRESSURES NEAR THIS WAVE IN THE GULF...ALTHOUGH THE SIGNAL HAS DAMPENED OVER THE PAST SEVERAL HOURS. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 12N16W 8N26W 10N47W 10N64W. BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES... SCATTERED SHOWERS AND TSTMS ARE WITHIN 60 NM S OF THE AXIS BETWEEN 25W-36W. DISCUSSION... GULF OF MEXICO... A WELL DEFINED UPPER LOW IS CENTERED ACROSS THE MID GULF NEAR 27N89W. INSTABILITY ASSOCIATED WITH THIS UPPER CIRCULATION AND S-SWLY FLOW ALOFT E OF THE CENTER IS ADVECTING MOISTURE ACROSS THE ERN HALF OF THE GULF AND FLORIDA. MOST OF THE ASSOCIATED TSTM ACTIVITY FROM EARLIER HAS DIMINISHED THOUGH LEFTOVER ISOLATED SHOWERS/TSTMS ARE IN THE S CENTRAL GULF LIKELY ENHANCED SOME BY A TROPICAL WAVE IN THE REGION. CONVECTION REMAINS FIRED UP OVER SRN MEXICO AND IN THE BAY OF CAMPECHE. DIFFLUENCE ALOFT APPEARS TO BE THE PRIMARY TRIGGER THOUGH NO DOUBT THERE IS INFLUENCE FROM THE NEARBY TROPICAL WAVE AND SMALLER SCALE FLOWS. THE SFC PATTERN IS VERY TRANQUIL WITH WEAK RIDGING FROM THE ATLC STRETCHING JUST N OF THE AREA. THIS IS KEEPING E TO SELY SFC FLOW ON THE LIGHT SIDE. LITTLE CHANGE IN THE SFC PATTERN IS EXPECTED OVER THE NEXT COUPLE OF DAYS SO WINDS ARE ANTICIPATED TO REMAIN LIGHT. CARIBBEAN SEA... MOST OF THE CARIB IS FAIRLY QUIET THIS MORNING THOUGH THERE ARE A FEW AREAS EXPERIENCING SOME UNSETTLED WEATHER. THE MOST ACTIVE IS IN THE SW CARIB WHERE A TROPICAL WAVE IS ENHANING ITCZ RELATED CONVECTION...SEE ABOVE FOR DETAILS. ELSEWHERE MUCH OF THE SENSIBLE WEATHER/MOISTURE APPEARS RELATED TO FEATURES ALOFT. THE MID AND UPPER PATTERN CONSISTS OF A N-S STRETCHED HIGH PRES RIDGE CENTERED OVER CENTRAL CUBA AND AN ELONGATED TROUGH EXTENDING FROM THE ATLC ACROSS THE NRN LEEWARDS TOWARD THE COAST OF COLOMBIA. STRONG N TO NELY FLOW BETWEEN THESE FEATURES HAS BLOWN OFF LAST EVENING'S TSTM ACTIVITY OVER E CUBA AND HISPANIOLA INTO THE COASTAL WATERS TO NEAR JAMAICA. NEARLY ALL OF THE SHOWERS ARE DIMINISHING EXCEPT FOR ONE CLUSTER TO THE S OF HAITI WHICH ACTUALLY LOOKS LIKE IT'S EXPANDING. MUCH OF THE REMAINDER OF THE CENTRAL CARIB LIES IN AN UPPER CONFLUENT ZONE HELPING TO SINK AND SUPPRESS DEEP CLOUD COVER. HIGH LEVEL CLOUDINESS LIES OVER THE E CARIB ON THE E SIDE OF THE TROUGH AND OVER THE W CARIB EMBEDDED WITHIN THE RIDGE. ATLANTIC OCEAN... THE SFC PATTERN ACROSS THE ATLC DISCUSSION AREA REMAINS WEAK THIS MORNING. THIS WEAK PATTERN IS MAINLY DUE TO AN UNUSUAL (FOR AUGUST) COLD FRONT DEEP INTO THE SUBTROPICS ENTERING THE AREA NEAR 32N42W TO A 1012 MB LOW NEAR 28N52W CONTINUING ALONG 25N60W THEN DISSIPATING TO 31N67W. A RECENT QSCAT PASS DEPICTED THIS BOUNDARY WELL...MARKING IT AS A PRONOUNCED NLY WIND SHIFT AND INCREASE TO 20 KT ON THE N SIDE NEAR THE LOW. SATELLITE IMAGERY ALSO SHOWS SCATTERED SHOWERS WITHIN 60 NM AHEAD OF THE BOUNDARY AND A SCATTERED STABLE STRATOCUMULUS DECK BEHIND IT. A WEAK LOW-LEVEL TROUGH IS ANALYZED ALONG 55W FROM 15N-21N. THIS BOUNDARY IS NOT PRODUCING ANY SIGNIFICANT SHOWER ACTIVITY BUT DOES SHOW UP WELL IN CLOUD DRIFT WINDS AND ON SATELLITE IMAGERY. THESE LOW-LATITUDE BOUNDARIES HAVE GREATLY BROKEN UP THE TYPICAL SUBTROPICAL RIDGING ALLOWING TRADES TO BE FAIRLY LIGHT ACROSS THE BULK OF THE AREA. IN THE MID AND UPPER LEVELS...A RIDGE IS OVER THE W ATLC CENTERED VERY NEAR BERMUDA. A DIFFLUENT PATTERN LIES AT THE W EDGE OF THE RIDGE ASSOCIATED WITH SOME TROUGHING OVER THE BAHAMAS AND IN THE GULF OF MEX. THIS DIFFLUENCE IS PRODUCING A FAIR AMOUNT OF CLOUDINESS ACROSS THE AREA W OF 76W. A LARGER SCALE TROUGH...THE SUPPORT FOR THE FRONT DISCUSSED ABOVE...IS OVER THE CENTRAL ATLC EXTENDING FROM 32N45W TO AN UPPER LOW NEAR 22N57W CONTINUING INTO THE E CARIB. A DOMINATING WELL DEFINED RIDGE TAKES OVER IN THE E ATLC WITH THE MAIN ANTICYCLONE CENTERED NEAR 20N37W. OUTSIDE OF THE AREAS OUTLINED IN THE ABOVE PARAGRAPH...DRY AIR ALOFT IS WIDESPREAD ON WATER VAPOR IMAGERY. $$ CANGIALOSI