000 AXNT20 KNHC 041754 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT WED JUN 04 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... A WELL-DEFINED TROPICAL WAVE ALONG 40W S OF 20N IS MOVING W 10-15 KT...WITH A WEAK 1012 MB CIRCULATION EMBEDDED ALONG THE AXIS NEAR 10N. ALTHOUGH THE WAVE CONTINUES TO DOMINATE A LARGE AREA...ASSOCIATED CONVECTION HAS BEEN NOTICEABLY DECREASING DURING THE LAST 24 HOURS. IN FACT...ALL THAT REMAINS IS A SMALL CONVECTIVE CLUSTER IMMEDIATELY NE OF THE WEAK SFC LOW ANALYZED 10N40W. A CURSORY LOOK AT REYNOLDS WEEKLY SEA SURFACE TEMPERATURES REVEALS THAT MOST OF THE WAVE LIES OVER A REGION WITH SSTS LESS THAN 26.5C...WHICH IS TOO COOL TO SUSTAIN ORGANIZED CONVECTION. TROPICAL WAVE IS IN THE E CARIBBEAN SEA ALONG 65W/66W S OF 17N MOVING W 10-15 KT. ALTHOUGH VISIBLE SATELLITE IMAGERY REVEALS NO CLEAR FEATURES ASSOCIATED WITH THE WAVE...MIMIC-TPW ANIMATION PROVES MORE HELPFUL IN SHOWING A PLUME OF ENHANCED MOISTURE CROSSING THROUGH THE EASTERN CARIBBEAN. IN ADDITION...TIME SERIES DATA FROM SAN JUAN AND SURROUNDING AREAS SHOW A NOTABLE INCREASE IN LOW- TO MID-LEVEL MOISTURE AND ANOMALOUS SLY FLOW ACROSS THE REGION IN ITS WAKE. LITTLE ASSOCIATED DEEP CONVECTION IS NOTED IN ASSOCIATION WITH THIS FEATURE. TROPICAL WAVE IS IN THE CARIBBEAN ALONG 81W S OF 17N MOVING W 10-15 KT. THIS WAVE CONTINUES TO BE A CHALLENGE TO TRACK AS THERE IS NO WELL-DEFINED...LOW-LEVEL CLOUD SIGNATURE EVIDENT IN VISIBLE SATELLITE IMAGERY. ITS CURRENT POSITION IS BASED PRIMARILY ON EXTRAPOLATION AND WEAK CYCLONIC SHEAR S OF 15N. WIDELY SCATTERED MODERATE CONVECTION IS OVER THE W CARIBBEAN SEA FROM 12N-19N BETWEEN 76W-85W. SOME OF THIS CONVECTION COULD BE ASSOCIATED WITH THE WAVE...ENHANCED BY THE END OF A MID- TO UPPER-LEVEL TROUGH EXTENDING SW INTO THE NW CARIBBEAN. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 07N12W TO 03N26W TO 2S31W TO 05N38W. LARGE CLUSTERS OF SCATTERED MODERATE TO STRONG CONVECTION ARE MOVING OFF THE W AFRICAN COAST FROM 4N-14N BETWEEN 11W-18W. OTHER CLUSTERS OF MODERATE TO STRONG CONVECTION ARE OCCURRING WITHIN 360 NM EITHER SIDE OF AXIS BETWEEN 23W AND 36W. ELSEWHERE ...SCATTERED MODERATE ISOLATED CONVECTION IS OCCURRING BETWEEN 02S AND 06S BETWEEN 16W AND 22W. ...DISCUSSION... GULF OF MEXICO... WATER VAPOR IMAGERY...UPPER-AIR DATA...AND CLOUD-TRACKED WINDS INDICATE AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM THE FL PENINSULA WESTWARD THROUGH NE MEXICO. 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 CERTAINLY IS A BIT ANOMALOUS FOR THIS TIME OF YEAR. LOW-LEVEL SUBTROPICAL RIDGING BULGES WSW INTO THE GULF AND IS PROVIDING A GENERAL SE TO S 10 TO 15 KT FLOW OVER THE EASTERN HALF OF THE GULF...WHILE A STRONGER 15 TO 20 KT FLOW PREVAILS W OF 90W. THE ONLY DENSE CLOUD COVER OF NOTE IS OVER THE BAY OF CAMPECHE...WHERE VISIBLE SATELLITE IMAGERY SHOWS THE REMNANTS OF TROPICAL STORM ARTHUR TRUDGING SLOWLY WNW JUST SE OF VERA CRUZ. ALTHOUGH A FAIR AMOUNT OF CONVECTION HAD DEVELOPED IN ASSOCIATION WITH EX-ARTHUR OVERNIGHT...LITTLE REMAINS EARLY THIS AFTERNOON EXCEPT FOR A FEW CONVECTIVE ELEMENTS BLOWING SE BETWEEN VILLAHERMOSA AND CAMPECHE. WITH THE CENTER VERY NEAR THE COAST AND MOVING INLAND AND THE LATEST CIMMS ANALYSIS SHOWS UP TO 15 KT OF NW SHEAR ...THE CHANCE FOR RE-DEVELOPMENT SEEMS SLIM. OVER THE NEXT FEW DAYS...EXPECT THE STRONG MID- TO UPPER-LEVEL RIDGE TO SHIFT E/NE AS A DEEP SHORTWAVE TROUGH PUSHES OUT OF THE WESTERN STATES AND ONTO THE PLAINS. AS A RESULT...DEEP LOW PRESSURE SHOULD FORM OVER THE PLAINS AND LEAD TO A BRISK RETURN FLOW AND INCREASING SEAS ACROSS MUCH OF THE GULF DURING THE NEXT 36 TO 48 HOURS. ALTHOUGH WEAK...THE REMAINS OF ARTHUR SHOULD MOVE INLAND NW OF VERA CRUZ AND POSSIBLY ENHANCE RAINS OVER THE SIERRA MADRE ORIENTAL S OF TUXPAN. OTHERWISE...UNUSUALLY DRY CONDITIONS ARE EXPECTED OVER THE GULF THROUGH AT LEAST LATE WEEK. CARIBBEAN... WATER VAPOR AND CLOUD-TRACKED WINDS SHOW THE WESTERN END OF WEAK MID- TO UPPER-LEVEL RIDGING EXTENDING INTO THE EASTERN CARIBBEAN TO ABOUT 70W. TO THE W...A WELL-DEFINED MID- TO UPPER-LEVEL TROUGH INTERRUPTS THE CARIBBEAN RIDGING...WITH AN AXIS FROM THE WINDWARD PASSAGE TO AROUND 13N80W. AS MENTIONED...TWO TROPICAL WAVES ARE MARCHING WESTWARD UNDERNEATH THESE FEATURES...SEE ABOVE. THE SECOND WAVE...NOW ALONG 65/66W...HAS BEGUN TO INTERACT WITH THE MID- TO UPPER-LEVEL TROUGH HANGING INTO THE N CENTRAL CARIBBEAN...WHICH HAS RESULTED IN ENHANCED CLOUD COVER AND CONVECTION EXTENDING FROM JAMAICA AND HISPANIOLA NE INTO THE SW ATLC WATERS. WITH THE UPPER TROUGH LIKELY TO REMAIN NEARLY STATIONARY THE NEXT DAY OR TWO...THE FAVORABLE DIVERGENT FLOW ALOFT...ENHANCED INSTABILITY...AND THE TRANSIENT WAVE MOVING THROUGH THE REGION SHOULD LEAD TO SCATTERED TO LOCALLY NUMEROUS TSTMS E OF THE AXIS. SCATTERED CONVECTION IS ALSO FIRING ALONG THE NORTHERN END OF THE TROPICAL WAVE NOW ALONG 81W...POSSIBLY BECAUSE OF ITS INTERACTION WITH THE SAME UPPER-LEVEL TROUGH. ENHANCED CLOUD COVER AND SOME CONVECTION ALSO CONTINUE TO PLAGUE PARTS OF THE YUCATAN...BELIZE...AND GUATEMALA...IN A REGION WHERE THE ELY TRADES ARE MEETING A PERSISTENT MONSOONAL FLOW STILL DOMINATING THE TROPICAL EASTERN PACIFIC W OF 100W. OTHERWISE...NEAR NORMAL SURFACE RIDGING AND LIGHT TO MODERATE TRADES PREVAIL ACROSS THE CARIBBEAN BASIN. ATLANTIC... ENHANCED MID-LEVEL RIDGING EXTENDS FROM NW AFRICA TO N OF THE LESSER ANTILLES...WITH A PRONOUNCED BREAK NOTED W OF THERE BETWEEN 60-75W. WATER VAPOR IMAGERY REVEALS A TROUGH ACROSS THIS REGION EXTENDING FROM JUST W OF BERMUDA SSW TO THE WINDWARD PASSAGE. A FAVORABLE DIFFLUENT FLOW ALOFT...ENHANCED LOW-LEVEL MOISTURE ASSOCIATED WITH THE NORTHERN END OF A TROPICAL WAVE OVER THE EASTERN CARIBBEAN...AND ENHANCED INSTABILITY ARE RESULTING IN A LARGE AREA OF CLOUD COVER AS WELL AS A SOLID AREA OF CONVECTION FROM 20-23N BETWEEN 65W TO THE SERN BAHAMAS. MODELS SHOW THE TROUGH EDGING EASTWARD DURING THE NEXT 12 TO 24 HOURS AND ULTIMATELY LIFTING OUT BUT NOT BEFORE DEPOSITING A CYCLONIC CIRCULATION NEAR 25N64W BY FRI MORNING. INDICATIONS ARE THAT THIS FEATURE AS WELL AS ANOTHER SIMILAR ONE TO THE W WILL GET CAUGHT IN AN ENHANCED EASTERLY CURRENT TO THE S OF ENHANCED MID-LEVEL RIDGING OVER THE SW ATLC/SERN STATES LATER THIS WEEK. THIS COULD END UP PROVIDING PORTIONS OF THE BAHAMAS AND FL WITH SOME MUCH-NEED RAINFALL BY THE WEEKEND. ELSEWHERE...THE LATEST CIMSS SAHARAN AIR LAYER ANALYSIS REVEALS A LARGE AREA OF DUST AND STRONG SUBSIDENCE ASSOCIATED WITH THE TROPICAL WAVE ALONG 40W...FOLLOWED BY A SECOND AREA NOW EMERGING FROM NW AFRICA AHEAD OF THE NEXT WAVE. THE WAVE ALONG 40W APPEARS TO BE OF HIGH AMPLITUDE FOR THIS TIME OF YEAR...WITH AN EXTENSION AT LEAST TO 20N. 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 FOR SOME TIME. HOWEVER...EVEN THOUGH SEA SURFACE TEMPERATURES ARE ABOVE CLIMATOLOGICAL AVERAGES...THEY ARE STILL TOO COOL OVER MUCH OF THE TROPICAL ATLANTIC FOR TROPICAL CYCLONE DEVELOPMENT. $$ KIMBERLAIN