000 AXNT20 KNHC 051819 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT THU JUN 05 2008 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF SOUTH AMERICA...AND 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 1715 UTC. ...TROPICAL WAVES... TROPICAL WAVE IS INTRODUCED ALONG 23W S OF 16N MOVING W 15 KT. SOUNDING DATA FROM DAKAR STILL REVEALS A STRONG RISE/FALL COUPLET IN SEVERAL DIFFERENT FIELDS...WITH THE MOST NOTABLE BEING 2-3 MB PRESSURE RISES TODAY IN THE WAKE OF THIS FEATURE. MIMIC-TPW ANIMATION ALSO SHOWS A NEW SURGE OF DEEP MOISTURE RISING TO 15N ALONG 20W IN ASSOCIATION WITH THIS WAVE....AND THE LATEST SFC ANALYSIS SHOWS A NORTHWARD RISE IN THE ITCZ. ALTHOUGH RECENT METEOSAT IMAGERY IS UNAVAILABLE...MORNING IMAGES DID INDICATE SCATTERED TO WIDESPREAD CONVECTION FROM 04N TO 09N BETWEEN 21W AND 28W...IN AN UNUSUAL LOCATION W OF THE AXIS. TROPICAL WAVE IS ALONG 49W S OF 21N IS MOVING W 15 KT. DEEP CONVECTION IS ENTIRELY ABSENT...AS THE WAVE IS MOVING OVER SUB-26.5C SEA SURFACE TEMPERATURES OVER THE TROPICAL ATLANTIC. COINCIDING WITH THE LOSS OF ALL DEEP CONVECTION...THE WAVE HAS BECOME HARDER TO DISCERN USING MIMIC-TPW ANIMATION. IN FACT... A BROAD CYCLONIC ENVELOPE WAS NOTED YESTERDAY IN MIMIC-TPW IMAGERY ...WHICH IS IN SHARP CONTRAST TO TODAYS MORNING DISORGANIZED APPEARANCE. IN ADDITION...A WEAK CYCLONIC CIRCULATION STILL EXISTS AT THE BASE OF THE WAVE...THOUGH IT TOO IS LOSING ITS ORGANIZATION. TROPICAL WAVE IS IN THE W CENTRAL CARIBBEAN ALONG 75W S OF 16N MOVING W 10-15 KT. LITTLE TO NO DEEP CONVECTION IS ASSOCIATED WITH THIS FEATURE ANY LONGER...AND THERE IS NO HINT OF A CYCLONIC CURVATURE TO THE LOW-LEVEL WIND. HOWEVER...TIME SERIES DATA FROM CURACAO DOES INDICATE A MAXIMUM IN THE 850 MB WINDS TODAY...POSSIBLY A SIGN OF THE WAVES EXISTENCE. OTHER SOUNDING DATA FROM THE CARIBBEAN DOES NOT APPEAR USEFUL...AS THE WAVE REMAINS OF FAIRLY LOW AMPLITUDE. GIVEN THE DIFFICULTY IN ESTABLISHING THE WAVES POSITION...THE WAVE IS LARGELY BEING EXTRAPOLATED WESTWARD. TROPICAL WAVE IN THE W CARIBBEAN ALONG 87/88W HAS BECOME DIFFICULT TO FIND USING CONVENTIONAL DATA. THIS CASE IS NOT ISOLATED...AS SEVERAL OF THE MOST RECENT WAVES MOVING ACROSS THIS REGION HAVE PROPAGATED INTO THE HIGHLY ANOMALOUS ENVIRONMENT WHICH HAS PREVAILED IN THE VICINITY OF CENTRAL AMERICA AND THE TROPICAL EAST PACIFIC S OF MEXICO SINCE LATE MAY. THE ANOMALOUS ENVIRONMENT IS CHARACTERIZED BY A LACK OF EASTERLY TRADES BLOWING ACROSS CENTRAL AMERICA AND THE TROPICAL EAST PACIFIC E OF 100W...WITH AN UNUSUAL LOW-LEVEL WLY FLOW IN PLACE INSTEAD. AS THE WAVE HAS BECOME ASSIMILATED INTO THIS MONSOON-TYPE ENVIRONMENT..IT IS NOW CARRIED AS A TROUGH AND IS EXTRAPOLATED FORWARD. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 12N16W TO 03N27W TO 00N35W TO 01S47W. METEOSAT IMAGERY IS UNAVAILABLE AT THIS HOUR TO DESCRIBE CURRENT CONVECTION. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY AND UPPER-AIR DATA INDICATE AN AMPLIFIED MID- TO UPPER-LEVEL RIDGE SITS OVER THE EASTERN THIRD OF THE COUNTRY...WITH THE RIDGE CENTER JUST N OF THE FL PANHANDLE. STRONG LARGE-SCALE SINKING ASSOCIATED WITH THE RIDGE IS CARVING OUT A LARGE AREA VOID OF ANY ORGANIZED CONVECTION...NOT TO MENTION ANY SIGNIFICANT CLOUD COVER. IT SHOULD BE NOTED THAT THE LACK OF DEEP CONVECTION OVER THE GULF REGION FOR SEVERAL DAYS IN A ROW NOW CERTAINLY IS A BIT ANOMALOUS FOR THIS TIME OF YEAR. LOW-LEVEL SUBTROPICAL RIDGING BULGES WSW FROM THE ATLANTIC INTO THE GULF AND IS PROVIDING A GENERAL SE 10 TO 15 KT FLOW OVER THE EASTERN HALF OF THE GULF...WHILE A SE TO S 20 TO 25 KT FLOW PREVAILS W OF 90W. THE ONLY CLOUD COVER OF NOTE IS OVER THE BAY OF CAMPECHE IN ASSOCIATION WITH A WEAK MID-LEVEL CYCLONIC CIRCULATION NOTED NEAR 19N97W. ISOLATED CONVECTION POSSIBLY RELATED TO THIS FEATURE IS BEGINNING TO DEVELOP ALONG THE W COAST OF THE YUCATAN PENINSULA. A STRONG CUT-OFF CYCLONE EMBEDDED WITHIN AN UNUSUALLY DEEP AND BROAD TROUGH OF LOW PRESSURE OVER THE WESTERN HALF OF THE COUNTRY WILL BE FORCED NE INTO THE NORTHERN PLAINS AND UPPER MIDWEST TODAY THROUGH FRI...BLOCKED BY THE AMPLIFIED RIDGE NOW OVER THE EASTERN STATES. AS A RESULT...A STRENGTHENED PRESSURE GRADIENT BETWEEN DEEP SFC LOW PRESSURE OVER THE PLAINS AND RELATIVE HIGH PRESSURE TO THE EAST SHOULD LEAD TO STRONG RETURN FLOW OF UP TO 30 KT AND SEAS BUILDING UP TO 8 TO 11 FT OVER THE NW GULF WATERS. WINDS SHOULD DECREASE TO 15 TO 20 KT ACROSS THE GULF BY FRI AFTERNOON...WITH LITTLE CHANGE TO CURRENT PATTERN GOING INTO THE WEEKEND. CARIBBEAN... WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS SHOW THE WESTERN END OF A WEAK MID- TO UPPER-LEVEL RIDGE EXTENDING INTO THE EASTERN CARIBBEAN TO ABOUT 73W. TO THE W...A WEAKENING MID- TO UPPER- LEVEL TROUGH INTERRUPTS THE CARIBBEAN RIDGING...WITH AN AXIS EXTENDING FROM THE WINDWARD PASSAGE TO AROUND 15N80W. EVEN THOUGH THE UPPER TROUGH IS GRADUALLY WEAKENING...THE FAVORABLE DIVERGENT FLOW ALOFT...ENHANCED INSTABILITY...AND THE PRESENCE OF A TRANSIENT WAVE NOW ALONG 75W MOVING THROUGH THE REGION SHOULD LEAD TO SCATTERED CONVECTION ACROSS JAMAICA AND HISPANIOLA TODAY. HOWEVER...IT APPEARS AS IF THE MAIN FOCUS OF THE CONVECTION WILL REMAIN N OF HISPANIOLA THIS AFTERNOON AND THIS EVENING...SIMILAR TO YESTERDAY. SCATTERED CONVECTION IS ALSO BEGINNING TO BREAK OUT OVER COASTAL SECTIONS FROM COSTA RICA THROUGH NE HONDURAS...VERY CLOSE TO THE REGION WHERE THE ELY TRADES ARE MEETING THE WEAK MONSOON-TYPE WESTERLY FLOW FROM THE TROPICAL EAST PACIFIC. IN ADDITION...ENHANCED CLOUD COVER AND SCATTERED CONVECTION CONTINUES TO PLAGUE PARTS OF THE YUCATAN ...BELIZE...AND GUATEMALA...NEAR WHERE THE LATEST TROPICAL WAVE IN A SERIES HAS BECOME ASSIMILATED INTO A LARGER-SCALE MONSOON GYRE NEAR OR JUST S OF THE ISTHMUS OF TEHUANTEPEC. OVER THE NEXT FEW DAYS...THE NARROW MID- TO UPPER-LEVEL TROUGH OVER THE N CENTRAL CARIBBEAN SHOULD DISSIPATE...THOUGH THE TROUGH WILL LEAVE BEHIND AN UPPER TROPOSPHERIC COLD LOW N OF HISPANIOLA. ITS PRESENCE SHOULD CONTINUE TO ENHANCE THE POTENTIAL FOR CONVECTION OVER THE N CENTRAL CARIBBEAN. OTHERWISE...UNDER CLIMATOLOGICALLY AVERAGE TO SLIGHTLY BELOW AVERAGE SUBTROPICAL RIDGING...MODERATELY STRONG TRADES SHOULD PREVAIL E OF 75W...WHILE LIGHT TO MODERATE TRADES PREVAIL ELSEWHERE. ATLANTIC... ENHANCED MID-LEVEL RIDGING GENERALLY EXTENDS FROM 40W TO NE OF THE LESSER ANTILLES...WITH A PRONOUNCED BREAK IN SUBTROPICAL RIDGING W OF THERE FROM 55-75W. WITHIN THIS BREAK...WATER VAPOR IMAGERY INDICATES A VIGOROUS MID- TO UPPER-LEVEL COLD LOW NEAR 25N66W MOVING LITTLE. HOWEVER...THE LARGER-SCALE TROUGH IN WHICH ITS EMBEDDED APPEARS TO BE EDGING EAST. A FAVORABLE DIFFLUENT FLOW ALOFT E OF THE TROUGH AXIS...ENHANCED MOISTURE AT ALL LEVELS ...AND ENHANCED INSTABILITY ARE RESULTING IN A LARGE AREA OF CLOUD COVER AS WELL AS A GROWING AREA OF CONVECTION WITHIN 120 NM EITHER SIDE OF A LINE FROM 20N69W TO 25N62W. SPORADIC CONVECTION IN THE VICINITY OF THE COLD LOW AND E OF THE UPPER TROUGH SHOULD PERSIST THROUGH FRI...WITH MODELS SHOWING THE COLD LOW HEADING W BY THE WEEKEND IN AN ELY CURRENT ALOFT. IN THE END...THIS SHOULD RESULT IN A GRADUAL INCREASE IN RAIN CHANCES OVER THE BAHAMAS AND EVENTUALLY THE FL PENINSULA SAT THROUGH MON. ELSEWHERE...THE LATEST CIMSS SAHARAN AIR LAYER ANALYSIS REVEALS A LARGE AREA OF DUST AND STRONG SUBSIDENCE ASSOCIATED WITH THE WAVE JUST NOW EMERGING FROM NW AFRICA AND SPREADING AS FAR E AS 40W. THE PRESENCE OF THE SAL SURROUNDING THE NEWEST WAVE TO MOVE OFFSHORE IS LIKELY INHIBITING CONVECTION OVER THE AREA N OF 11N. OTHERWISE...CIMSS SHEAR ANALYSES AS WELL AS CIRA EXPERIMENTAL GENESIS PRODUCTS SHOW MUCH LOWER-THAN-AVERAGE VERTICAL WIND SHEAR S OF ABOUT 18N E OF 55W...A TREND WHICH HAS CONTINUED SINCE AT LEAST MAY. IN FACT...THE AREA AVERAGE SHEAR ACROSS THE TROPICAL ATLANTIC IS LESS THAN 20 KT...WHEN IT SHOULD BE MUCH CLOSER TO 30 KT. DESPITE THE EARLIER-THAN-NORMAL DYNAMIC POTENTIAL OVER THE TROPICAL ATLANTIC...ABOVE NORMAL SEA SURFACE TEMPERATURES ARE STILL TOO COOL OVER MUCH OF THE TROPICAL ATLANTIC FOR TROPICAL CYCLONE DEVELOPMENT. $$ KIMBERLAIN