000 AXNT20 KNHC 071803 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT SUN OCT 07 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURE... A BROAD 1004 MB LOW PRESSURE AREA IS OVER THE NW CARIBBEAN SEA NEAR 17N82W. THE SYSTEM IS GENERATING SCATTERED SHOWERS AND TSTMS N OF 12N W OF 78W. THE STRONGEST CLUSTER OF CONVECTION IS JUST E OF BELIZE WITHIN 60 NM OF 16.5N87W. THE SURROUNDING BUOY AND SHIP OBSERVATIONS HAVE INDICATED ABOUT A 2-3 MB DROP IN PRESSURE OVER THE PAST 24 HOURS. HOWEVER...THE OVERALL CIRCULATION REMAINS RATHER ILL DEFINED AND THE SFC WINDS REMAIN ON THE LIGHT SIDE. NONETHELESS...UPPER LEVEL WINDS ARE GRADUALLY BECOMING MORE FAVORABLE AND SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE OVER THE NEXT FEW DAYS AS IT REMAINS QUASI-STATIONARY. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 54W S OF 20N MOVING W TO NW NEAR 10 KT. A 1009 MB LOW IS LOCATED ALONG THE WAVE AXIS NEAR 17N. THE CIRCULATION REMAINS AN EXPOSED LOW LEVEL SWIRL...WITH MOST OF THE LIMITED SHOWER/TSTM ACTIVITY E OF THE CENTER FROM 13N-18N BETWEEN 49W-54W. DEVELOPMENT OF THIS SYSTEM IS NOT ANTICIPATED DUE TO UNFAVORABLE UPPER LEVEL WINDS. ...THE ITCZ... AXIS IS CENTERED ALONG 11N15W 7N30W 10N51W 9N62W. THE ITCZ REMAINS FAIRLY ACTIVE THIS AFTERNOON. SCATTERED MODERATE CONVECTION COVERS THE LARGE AREA OVER THE TROPICAL ATLANTIC FROM 3N-11N BETWEEN 21W-50W. THERE MAY BE A WEAK LOW AMPLITUDE WAVE OR TWO EMBEDDED IN THIS REGION...BUT HAVE HELD OFF ADDING ANYTHING AT THIS POINT DUE TO THE HIGHLY ZONAL NATURE OF THE AXIS...WHICH IS MAKING ANY WAVES THAT DO EXIST DIFFICULT TO TRACK. DISCUSSION... THE GULF OF MEXICO... MODERATE TO FRESH ELY SFC WINDS PERSIST OVER THE E GULF IN RESPONSE TO A TIGHTENED PRES GRADIENT BETWEEN LOW PRES IN THE NW CARIBBEAN AND HIGH PRES OVER THE MID-ATLANTIC STATES. THIS STIFF FLOW IS BLOWING ISOLATED...MOSTLY SHALLOW SHOWERS FROM THE ATLC ACROSS FLORIDA AND INTO THE E GULF WATERS. THE SFC FLOW REMAINS LIGHTER W OF 93W AS THE GRADIENT RELAXES. SCATTERED SHOWERS AND TSTMS ARE A LITTLE MORE CONCENTRATED BETWEEN THE YUCATAN PENINSULA AND WRN LOUISIANA. THIS ACTIVITY IS ASSOCIATED WITH DEEP LAYER INVERTED TROUGHING WHICH EXTENDS NWD FROM THE SPECIAL FEATURE IN THE NW CARIB. SKY CONDITIONS ACROSS MOST OF THE W GULF W OF 93W ARE MOSTLY CLEAR TO FEW UNDER A MODERATE SUBSIDENT ENVIRONMENT SUPPORTED BY A CONFLUENT UPPER PATTERN. ELY WINDS ARE EXPECTED TO REMAIN MODERATE TO FRESH IN THE E AND CENTRAL GULF OVER THE NEXT DAY OR SO AS THE MOISTURE PLUME AND TROUGHING FROM THE CARIBBEAN DRIFT W. THE CARIBBEAN SEA... THE MAIN AREA OF FOCUS CONTINUES TO BE THE SPECIAL FEATURE BETWEEN ERN HONDURAS AND THE CAYMAN ISLANDS...WHICH IS BEING MONITORED FOR SLOW DEVELOPMENT. SEE ABOVE FOR DETAILS. ELSEWHERE...WIDELY SCATTERED MODERATE CONVECTION IS BETWEEN 69W-78W...BETWEEN SOUTH AMERICA AND HISPANIOLA. THIS IS SUPPORTED BY CONVERGENT LOW LEVEL FLOW BETWEEN THE S/SW FLOW AROUND THE SPECIAL FEATURE COLLIDING WITH LIGHT TO MODERATE E-SE TRADE FLOW OVER THE ERN CARIBBEAN. UPPER FLOW IS ALSO DIFFLUENT OVER THIS REGION BETWEEN TROUGHING OVER THE NW PORTION AND RIDGING EXTENDING N ALONG 70W. TRADE FLOW IS EXPECTED TO REMAIN INTERRUPTED OVER THE NEXT DAY OR SO...WITH THE LOW IN THE NW PORTION AND TROUGHING PERSISTING IN THE SW NORTH ATLC. THE EXCEPTION WILL BE MORE OF A NORMAL MODERATE E/ESE BREEZE BETWEEN THE ABC ISLANDS AND HISPANIOLA. THE ATLANTIC OCEAN... MUCH OF THE CENTRAL AND WRN PORTION OF THE DISCUSSION AREA IS DOMINATED BY AN ELONGATED SFC TROUGH THAT EXTENDS FROM NEAR 28N35W ALL THE WAY BACK TO THE SE BAHAMAS. THE EVOLUTION OF THIS STRETCHED OUT SFC TROUGHING HAS BEEN THE COMBINED EFFECT OF AN OLD FRONTAL BOUNDARY...A PAIR OF EX-TROPICAL CYCLONES (KAREN AND MELISSA)...ENERGY FROM THE TROPICAL WAVE NOW ALONG 54W...AND A SERIES OF UPPER LOWS AND ASSOCIATED UPPER TROUGHING. NEEDLESS TO SAY...THE SYSTEM IS VERY COMPLEX. THERE ARE A COUPLE OF AREAS ALONG THE TROUGHING WHERE LOW LEVEL VORTICITY APPEARS TO BE MAXIMIZED. IN PARTICULARLY NEAR 26N54W AND 24N69W. NEITHER OF THESE AREAS ARE GENERATING VERY ORGANIZED TSTM ACTIVITY AT THE MOMENT THOUGH. HOWEVER...SCATTERED MODERATE CONVECTION IS NORTH OF PUERTO RICO FROM 20N-25N BETWEEN 65W-69W...AND FURTHER E FROM 24N-26N BETWEEN 58W-64W...AND FINALLY FROM 24N-30N BETWEEN 42W-54W. ELY WINDS REMAINS MODERATE TO FRESH N OF THE TROUGHING DUE TO THE TIGHTENED GRADIENT BETWEEN THE TROUGH AND HIGH PRES OVER THE MID ATLC COAST. GFS CONTINUES TO DEVELOP A SERIES OF LOW PRES AREAS ALONG THE TROUGHING OVER THE NEXT SEVERAL DAYS THAT MOVE NE/ENE ALONG THE BOUNDARY...BUT CURRENTLY HAVE LOW CONFIDENCE IN THESE LOWS WITH FAIRLY WIDE DIVERGENCE BETWEEN THE GLOBAL MODELS. MUCH QUIETER WEATHER EXISTS E OF 35W. THE MAIN MID TO UPPER LEVEL FEATURE OVER THE TROPICS IS AN ANTICYCLONE CENTERED NEAR 11N37W. IN THE SUBTROPICS...THE UPPER FLOW IS QUITE STRONG OUT OF THE W TO SW ON THE N SIDE OF THE TROPICAL RIDGE. THIS SWIFT FLOW IS SPREADING DEBRIS MOISTURE ACROSS MUCH OF THE AREA N OF 23N W OF THE CANARY ISLANDS...EXCEPT FOR MUCH DRIER AIR N OF 25N BETWEEN 20W-30W...BEHIND AN UPPER TROUGH. THE SFC PATTERN IS RATHER TRANQUIL WITH A 1022 MB HIGH CENTERED NEAR 29N28W. THIS IS KEEPING WINDS LIGHT IN THE SUBTROPICS AND MODERATE IN THE TROPICS...EXCEPT SLIGHTLY STRONGER 20-25 KT NLY WINDS OFF THE COAST OF NW AFRICA WHERE THE GRADIENT REMAINS TIGHTER PER USUAL. $$ WILLIS