000 AXNT20 KNHC 280004 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SAT AUG 27 2011 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2200 UTC. ...SPECIAL FEATURE... THE CENTER OF HURRICANE IRENE WAS LOCATED NEAR 36.2N 76.0W AT 2100Z...OR ABOUT ABOUT 50 MI SSE OF NORFOLK VIRGINIA AND ABOUT 340 MI SSW OF NEW YORK CITY...MOVING TOWARD THE NORTH-NORTHEAST OR 15 DEGREES AT 11 KT. MINIMUM CENTRAL PRESSURE WAS ESTIMATED AT 950 MB. MAXIMUM SUSTAINED WIND SPEED WAS 70 KT WITH GUSTS TO 85 KT. PLEASE SEE THE LATEST INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADER MIATCPAT4/WTNT34 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADER MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. THE CENTER OF IRENE WAS MOVING ACROSS CURRITUCK SOUND ACROSS FAR NE NORTH CAROLINA...WITH THE E HALF OF THE CORE CIRCULATION MOVING OVER THE COAST AND IMMEDIATE COASTAL WATERS. RAINBANDS WITH NUMEROUS MODERATE TO STRONG CONVECTION WERE OCCURRING WITHIN 90 NM ACROSS THE NE AND 30 NM SW SEMICIRCLES...WHILE VERY LONG RAINBANDS WITH NUMEROUS MODERATE ISOLATED STRONG CONVECTION WERE OCCURRING FROM NEW JERSEY AND SOUTHEAST PENNSYLVANIA AND SPIRALING SOUTHWEST AND THEN SOUTH ACROSS MARYLAND...VIRGINIA AND INTO EASTERN NORTH CAROLINA...ALL LEAVING VERY HEAVY TO TORRENTIAL RAINFALL. IRENE IS FORECAST TO MOVE NNE ACROSS THE COASTAL WATERS OF VIRGINIA...MARYLAND AND DELAWARE IN THE NEXT 6 TO 8 HOURS AND THEN BEGIN TO ACCELERATE SUNDAY MORNING AS IT BRUSHES THE NEW JERSEY COASTLINE AND MOVES ASHORE FOR GOOD ACROSS PORTIONS OF LONG ISLAND NEW YORK. SOME GRADUAL WEAKENING IS EXPECTED OVERNIGHT...WITH IRENE EXPECTED TO REACH COASTAL NEW YORK AT JUST UNDER HURRICANE STRENGTH. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH IS ANALYZED MEANDERING ACROSS THE SAHARAN DESERT THEN SW TO THE COASTAL WATERS OF GUINEA-BISSAU TO A DEVELOPING 1011 MB SURFACE LOW NEAR 10N17W ASSOCIATED WITH A TROPICAL WAVE THAT HAS MOVED OFF THE COAST OF AFRICA. NUMEROUS MODERATE TO STRONG CONVECTION WAS OCCURRING FROM 06N TO 11N BETWEEN 19W AND 23W. A 1011 MB LOW...REMNANTS OF T.D. TEN...WAS CENTERED NEAR 17.5N35W MOVING SLOWLY NW WITH A SURFACE TROUGH EXTENDING NE TO SW THROUGH THE LOW FROM 23N31W TO 11N43W TO TON48W WHERE IT TRANSITIONED TO ITCZ ALONG 09.5N55W TO COASTAL VENEZUELA AT 08N60W. SCATTERED MODERATE ISOLATED STRONG CONVECTION WAS OCCURRING S OF THE TROUGH IN THE CONFLUENT LLVL SWLY FLOW FROM 09N TO 12N BETWEEN 36W AND 47W. A WEAK WAVE HAS DEVELOPED OVER THE PAST FEW DAYS IN LIGHT TRADEWIND FLOW E OF THE LESSER ANTILLES...AND WAS ALONG 59W FROM ABOUT 10N TO 16N AND DRIFTING W...WITH GOOD LLVL CONVERGENCE BETWEEN 13N AND 16N MAINTAINING ACTIVE MODERATE TO STRONG CONVECTION BETWEEN 56W AND 61W. ...DISCUSSION... GULF OF MEXICO... A MIDDLE TO UPPER LEVEL TROUGH LINGERS ACROSS THE NRN GULF FROM CENTRAL GEORGIA TO THE S TIP OF TEXAS WITH A NEW SHORTWAVE DIVING S ACROSS THE MS VALLEY POISED TO REINFORCE THIS TROUGH IN THE NEXT 24 HOURS. THIS IS YIELDING CONVERGENCE ALOFT N OF 27.5N. MILD W TO NW FLOW ALOFT PREVAILS ACROSS THE BASIN S OF THE NEARLY E TO W UPPER TROUGH...YIELDING MODEST DIVERGENCE ACROSS W PORTIONS ALONG 23N WERE SCATTERED SMALL TSTMS THAT DOTTED THE WATERS W OF 94.5W THIS AFTERNOON HAVE DIMINISHED. A WEAK 1013 MB HIGH WAS ANALYZED ACROSS THE NW GULF NEAR 26.5N94W THIS AFTERNOON AND WAS DEPICTED IN A 1536Z ASCAT PASS. LIGHT TO MODERATE WLY SFC FLOW PREVAILS N THROUGH E OF THIS HIGH TO THE FLORIDA PENINSULA...WITH LIGHT AND VARIABLE FLOW ACROSS THE SW GULF. DIURNAL CONVECTION HAS FLARED ACROSS THE YUCATAN PENINSULA YIELDING NUMEROUS SHOWERS AND TSTMS THAT WILL SHIFT W INTO THE SW GULF DURING THE EVENING HOURS AND DIMINISH VERY SLOWLY OVERNIGHT. A MID LEVEL WEAKNESS EXISTS JUST OFFSHORE OF THE W COAST OF THE YUCATAN PENINSULA AND IS FORECAST TO BECOME SOMEWHAT BETTER ORGANIZED IN THE NEXT FEW DAYS. THIS WILL MAINTAIN LOW TO MID LEVEL CONVERGENCE AND INSTABILITY ACROSS THE E HALF OF THE BAY OF CAMPECHE AND LARGE PORTIONS OF THE YUCATAN PENINSULA LEADING TO PERIODS OF ACTIVE CONVECTION. CARIBBEAN SEA... A MID TO UPPER LEVEL CYCLONE OF THE W CENTRAL ATLC EXTENDS A TROUGH SW ACROSS PUERTO RICO THEN S TO NEAR 13N67W. UPPER CONVERGENCE WAS OCCURRING TO THE NW OF THE AXIS ACROSS PUERTO RICO AND THE MONA PASSAGE WHILE SPEED DIVERGENCE WAS FOUND TO THE SE OF THE AXIS. WIDESPREAD AFTERNOON CONVECTION OCCURRING ACROSS THE SE CARIBBEAN SE OF THE TROUGH HAS DIMINISHED CONSIDERABLY RECENTLY AND WAS MORE ISOLATED AT 2200Z. AN ELONGATED RIDGE EXTENDED FROM THE W ATLC E OF IRENE SW TO AN UPPER ANTICYCLONE OVER THE NW CARIBBEAN...AND WAS YIELDING N TO NE FLOW ALONG ACROSS THE CENTRAL CARIBBEAN BETWEEN 69W AND 81W. A WEAK LOW LEVEL PERTURBATION ACROSS THE CENTRAL CARIBBEAN FROM COLOMBIA NNE TO S OF HISPANIOLA WAS TRANSPORTING A BROAD AREA OF ABUNDANT LOW LEVEL MOISTURE N AND NW THAT HAS RECENTLY IGNITED INTO SCATTERED TO NUMEROUS MODERATE CONVECTION. MILD DIRECTIONAL DIFFLUENCE ALOFT ACROSS THIS AREA WAS VENTING THIS CONVECTION NICELY. THIS PERTURBATION IS FORECAST TO SHIFT WNW IN THE NEXT FEW DAYS AND MAY BECOME BETTER ORGANIZED AS IT MOVES ACROSS THE SW PERIPHERY OF THE STRENGTHENING ATLC RIDGE. PRESENTLY...WEAK ANTICYCLONIC FLOW PREVAILS AT THE SFC ACROSS THE CARIBBEAN... WITH MODERATE E TO SE WINDS ACROSS THE EAST AND CENTRAL PORTIONS BECOMING LIGHT SE TO S ACROSS NW AND W PORTIONS. AS IRENE LIFTS FURTHER TO THE N AND NE DURING THE NEXT FEW DAYS LOOK FOR THE ATLC RIDGE TO BUILD BACK IN ACROSS THE BASIN AND BRING A RETURN TO MORE TYPICAL TRADEWINDS. ATLANTIC OCEAN... THE PRIMARY FOCUS ACROSS THE ATLC TODAY CONTINUES TO BE HURRICANE IRENE. FOR MORE INFORMATION ON IRENE...SEE SPECIAL FEATURES ABOVE. THE BROAD CYCLONIC WIND FIELD ENCOMPASSES THE NE GULF TO THE SW N ATLC ALONG ABOUT 69-70W...AND IS DRAWING TROPICAL MOISTURE FROM THE CARIBBEAN AND CENTRAL ATLC NWD ACROSS THE BAHAMAS AND SW N ATLC TO 69W...WHERE A FEW VERY LONG AND THIN BROKEN LINES OF CONVECTION CONTINUE TO DEVELOP THIS EVENING. E OF THIS...A WELL DEFINED 1008 MB LOW WAS CENTERED NEAR 28N64W. THIS LOW HAS BEEN CLEARLY EVIDENT IN SATELLITE IMAGERY THE PAST 24 HOURS WITH OCCASIONAL FLARES OF DEEP CONVECTION ACROSS THE SRN PERIPHERY. HOWEVER THIS SFC LOW WAS SHIFTING NW AND AWAY FROM THE UPPER CYCLONE OVER THE W CENTRAL ATLC NEAR 25N61W...AND INTO AN AREA OF WEAKENING UPPER SHEAR THAT ALLOWED FOR A SIGNIFICANT FLARE OF CONVECTION THIS AFTERNOON...THIS HAS SINCE DIMINISHED. THIS LOW IS FORECAST TO BE PULLED BY THE LARGE CIRCULATION OF IRENE TOWARD THE NW AND WEAKEN THE NEXT 24 HOURS. AN ELONGATED SURFACE TROUGH WAS LOCATED ABOUT 360 NM TO THE E OF THIS SFC LOW AND HAS BEEN MOVING IN TANDEM WITH THE LOW FOR THE PAST FEW DAYS. LLVL CONVERGENCE ON THE E SIDE OF THIS TROUGH WAS PRODUCING SCATTERED CONVECTION. WEAK HIGH PRES AND LIGHT TO MODERATE ANTICYCLONIC FLOW PREVAIL ELSEWHERE TO THE E OF THIS TROUGH AND NW OF FORMER T.D. TEN...IN AN AREA OF BROAD SUBSIDENCE AND FAIR WEATHER. AS MENTIONED ABOVE IN THE CARIB SECTION...THE ATLC SURFACE RIDGE WILL BUILD WEST AND SOUTHWESTWARD IN THE WAKE OF IRENE MONDAY THROUGH WEDNESDAY. ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ STRIPLING