000 AXNT20 KNHC 202345 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT THU AUG 20 2009 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2245 UTC. ...SPECIAL FEATURES... AS OF 2100 UTC...HURRICANE BILL IS CENTERED NEAR 23.8N 63.2W OR ABOUT 595 MILES...960 KM...S OF BERMUDA AND ABOUT 1080 MILES...1735 KM...SE OF CAPE HATTERAS NORTH CAROLINA MOVING NW OR 305 DEG AT 16 KT. THE LATEST MINIMUM CENTRAL PRESSURE IS 948 MB REPORTED BY AN AIR FORCE RECONNAISSANCE AIRCRAFT A FEW HOURS AGO. MAXIMUM SUSTAINED WIND SPEEDS HAVE INCREASED TO 110 KT WITH GUSTS UP TO 135 KT. HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 115 MILES...185 KM...FROM THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 260 MILES...415 KM. A TROPICAL STORM WARNING AND A HURRICANE WATCH HAVE BEEN ISSUED FOR BERMUDA. SEE THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS TCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS NEAR THE CENTER OF THE HURRICANE FROM 22N-25N BETWEEN 61W-64W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS OBSERVED IN THE OUTER RAINBANDS ESPECIALLY TO THE NE OF THE CENTER. LARGE SWELLS GENERATED BY BILL ARE AFFECTING THE NORTHERN LEEWARD ISLANDS...PUERTO RICO AND HISPANIOLA...AND SHOULD BEGIN AFFECTING THE BAHAMAS...BERMUDA...MOST OF THE U.S. EAST COAST...AND THE ATLANTIC MARITIMES OF CANADA DURING THE NEXT FEW DAYS. THESE SWELLS WILL LIKELY CAUSE EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 24W S OF 17N ACROSS THE CAPE VERDE ISLANDS MOVING W NEAR 10 KT. THE WAVE COINCIDES WITH A DEEP LAYERED MOISTURE MAXIMUM OBSERVED IN THE TOTAL PRECIPITABLE WATER IMAGERY. AN INVERTED-V LOW LEVEL SIGNATURE IS NOTED ON RECENT SATELLITE PICTURES WITH SOME CYCLONIC TURNING NEAR THE INTERSECTION OF THE WAVE WITH THE ITCZ. THIS IS CONFIRMED BY AN ASCAT SCATTEROMETER PASS FROM EARLIER TODAY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 12N-14N BETWEEN 25W-28W. A TROPICAL WAVE EXTENDS FROM 17N52W TO 7N49W MOVING W NEAR 20 KT. THIS WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE. A TROPICAL WAVE IS ACROSS THE YUCATAN PENINSULA ALONG 90W S OF 21N MOVING W NEAR 15 KT. THIS WAVE LIES WITHIN A BROAD DEEP LAYER MOISTURE MAXIMUM IN THE E PACIFIC OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 14N-20N BETWEEN 89W-94W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 13N13W 12N26W 9N33W 10N44W 8N55W 10N61W. A CLUSTER OF NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS JUST OFF THE AFRICA COAST FROM 11N-14N BETWEEN 16W-18W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 9N-11N BETWEEN 20W-22W. SIMILAR ACTIVITY IS FROM 7N-10N BETWEEN 28W-24W. ...DISCUSSION... GULF OF MEXICO... A WEAK SURFACE RIDGE IS ACROSS THE GULF OF MEXICO BUILDING FROM THE W ATLC. AN UPPER LEVEL RIDGE COVERS MOST OF THE GULF EXTENDING FROM ONE UPPER LEVEL HIGH CENTER E OF N CAROLINA NEAR 35N75W TO A SECOND UPPER LEVEL HIGH CENTERED OVER MEXICO NEAR 21N101W. AN OUTFLOW BOUNDARY N OF THE DISCUSSION AREA ACROSS MISSISSIPPI AND SRN ARKANSAS...AS WELL AS UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER RIDGE AND AN UPPER LEVEL TROUGH OVER THE N CENTRAL UNITED STATES ARE SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE NRN GULF N OF 27 E OF 95W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER RIDGE AND AN UPPER LEVEL LOW OVER BELIZE NEAR 18N88W IS SUPPORTING SHOWERS/THUNDERSTORMS IN THE ERN BAY OF CAMPECHE FROM 18N-20N BETWEEN 90W-92W. THIS ACTIVITY MAY BE ENHANCED BY THE TROPICAL WAVE ALONG 90W. THE REMAINDER OF THE SE GULF IS EXPERIENCING GENERALLY FAIR WEATHER UNDER THE INFLUENCE OF DRY AIR AND SUBSIDENCE ALOFT. EXPECT SHOWERS/THUNDERSTORMS TO REMAIN ACROSS THE SW GULF IN THE BAY OF CAMPECHE AS THE TROPICAL WAVE OVER THE YUCATAN MOVES WWD. CARIBBEAN SEA... A FEW ISOLATED SHOWERS ARE IN THE NW CARIBBEAN N OF HONDURAS DUE TO UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL LOW OVER BELIZE NEAR 18N88W AND AN UPPER LEVEL RIDGE OVER THE SW CARIBBEAN. SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE SW CARIBBEAN S OF 11N BETWEEN 75W-85W AFFECTING PANAMA AND COSTA RICA. THESE SHOWERS ARE GENERATED BY SURFACE CONVERGENCE NEAR THE E PACIFIC ITCZ AND A 1007 MB SURFACE LOW ALONG THE COAST OF COLUMBIA NEAR 10N76W. NARROW LINES OF SHOWERS ARE ACROSS THE FAR NE ISLANDS AS WELL AS ACROSS THE LESSER ANTILLES ASSOCIATED WITH CYCLONIC FLOW AROUND HURRICANE BILL. THE REMAINDER OF THE CARIBBEAN IS UNDER DRY SUBSIDENCE AIR ALOFT SUPPORTING GENERALLY FAIR WEATHER. MODERATE TRADEWINDS ARE ACROSS MUCH OF THE BASIN WITH STRONGER WINDS NEAR THE COAST OF COLUMBIA. ATLANTIC OCEAN... HURRICANE BILL REMAINS THE DOMINANT FEATURE ACROSS THE ATLC. SEE SPECIAL FEATURES FOR DETAILS. THE REMAINDER OF THE ATLC IS UNDER A BROAD RIDGE ANCHORED BY A 1029 MB AZORES HIGH NEAR 40N23W. BILL CONTINUES TO MOVE AROUND THE PERIPHERY OF THIS SFC RIDGE. IN THE UPPER LEVELS...A NARROW UPPER TROUGH IS E OF THE BAHAMAS WITH AXIS ALONG 73W. AN UPPER LEVEL RIDGE IS E OF THE STRONG OUTFLOW OF BILL CENTERED NEAR 24N53W. ANOTHER UPPER LEVEL HIGH DOMINATES THE E ATLC CENTERED NEAR 30N33W. $$ WALTON