Hurricane BILL ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE BILL DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 1100 AM AST WED AUG 19 2009 A NOAA P-3 PLANE ON A RESEARCH MISSION HAS BEEN PROVIDING EXCELLENT DATA FROM BILL DURING THE PAST SEVERAL HOURS. THERE WAS A PEAK FLIGHT-LEVEL WIND OF 132 KNOTS TWO HOURS AGO AND THE SFMR REPORTED PEAK WINDS AROUND 105 KNOTS. DATA FROM THE PLANE ALSO SHOW THAT BILL HAS A LARGE WIND FIELD AND A 30 NMI WIDE EYE. THE LATEST EXTRAPOLATED MINIMUM CENTRAL PRESSURE WAS 950 MB. ALTHOUGH THE RING OF DEEP CONVECTION SURROUNDING THE EYE OBSERVED ON SATELLITE HAS WEAKENED DURING THE PAST COUPLE OF HOURS...THE T-NUMBERS REMAIN AROUND 6.0 ON THE DVORAK SCALE. INITIAL INTENSITY IS KEPT AT 115 KT IN THIS ADVISORY. THE LARGE SCALE ENVIRONMENT IS FAVORABLE FOR ADDITIONAL INTENSIFICATION SINCE BILL IS HEADING FOR A WARMER OCEAN AND THE SHEAR IS EXPECTED TO BE LOW FOR THE NEXT TWO TO THREE DAYS. HOWEVER...MOST LIKELY THERE WILL BE FLUCTUATIONS IN INTENSITY IN THIS PERIOD CONTROLLED BY EYEWALL REPLACEMENT CYCLES. BEYOND 72 HOURS...THE OCEAN IS COOLER AND A GRADUAL WEAKENING SHOULD BEGIN... BUT BILL IS FORECAST TO REMAIN A HURRICANE THROUGH FIVE DAYS. THERE HAS BEEN NO CHANGE IN THE STEERING CURRENTS AND BILL CONTINUES TO MOVE TOWARD THE WEST-NORTHWEST OR 300 DEGREES AT 16 KNOTS AROUND THE AZORES-BERMUDA HIGH. THIS GENERAL MOTION SHOULD CONTINUE FOR A COUPLE OF DAYS. THEREAFTER...A LARGE MID-LATITUDE TROUGH IS EXPECTED TO SWING EASTWARD OVER THE EASTERN UNITED STATES...FORCING BILL TO TURN NORTHWARD A GOOD DISTANCE AWAY FROM THE U.S. EAST COAST. THIS IS IN AGREEMENT WITH THE SOLUTION PROVIDED BY MOST OF THE DYNAMICAL MODELS...WHICH IN FACT HAVE BEEN QUITE CONSISTENT IN TURNING BILL NORTHWARD FOR THE PAST SEVERAL RUNS. THE OFFICIAL FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND IS VERY CLOSE TO THE MODEL CONSENSUS. BECAUSE BILL IS A LARGE AND STRONG HURRICANE...SWELLS TRIGGERED BY THE HURRICANE SHOULD AFFECT THE NORTHERN LEEWARD ISLANDS...BERMUDA AND PORTIONS OF THE EASTERN UNITED STATES DURING THE NEXT FEW DAYS. FORECAST POSITIONS AND MAX WINDS INITIAL 19/1500Z 18.7N 56.3W 115 KT 12HR VT 20/0000Z 19.9N 58.3W 120 KT 24HR VT 20/1200Z 21.7N 61.0W 125 KT 36HR VT 21/0000Z 23.5N 63.5W 125 KT 48HR VT 21/1200Z 26.0N 65.5W 120 KT 72HR VT 22/1200Z 32.0N 68.5W 115 KT 96HR VT 23/1200Z 38.5N 67.0W 100 KT 120HR VT 24/1200Z 47.0N 58.0W 75 KT $$ FORECASTER AVILA NNNN
Hurricane Bill on August 18 
Following a period of steady intensification, Hurricane Bill is now a Category 4 major hurricane, as defined by the Saffir-Simpson Hurricane Scale.

Bill formed on August 12 and became the 2009 season's first hurricane on August 17. For the past few days, the storm has been moving toward the west-northwest, but that is expected to change later this week as it turns more toward the north. After that, its track is uncertain, though National Hurricane Center (NHC) forecasters believe the hurricane will pass between Bermuda and the United States.

As of 11 a.m. AST August 19 (0900 UTC August 19), Hurricane Bill was located within 15 nautical miles of 18.0°N 54.9°W, about 460 mi (740 km) east of the Leeward Islands. Maximum sustained winds were near 115 knots (135 mph, 215 km/h), with stronger gusts. Forecasters estimate the storm's minimum barometric pressure at 950 millibars.

Bermuda could be under the most significant threat from Bill, and officials there have been monitoring the storm's progress. Derrick Binns, Permanent Secretary of the Ministry of Labour, Home Affairs and Housing, reported that "We have been following the storm closely since its inception, and today we reviewed our planning and procedures to ensure all are in sync. While we have not as yet issued hurricane warnings, I think it is important to advise residents to check their emergency kits to be sure supplies are adequate." 
 

Bill is expected to spare the United States from any significant impact, but forecasters advise that since the storm is still several days away, nothing is certain. Indeed, residents of Long Island, New York are keeping a close eye on the cyclone's progress. 

Forecasters also warn that Bill could target parts of eastern Canada. Residents of Nova Scotia, mindful of the extensive damage from Hurricane Juan several years prior, are beginning to take precautionary measures. 

Regardless of its exact track, Bill will likely generate rough surf and dangerous rip tides along the coast of the U.S. and Canada. 

Tropical cyclones are known to be unpredictable, so interests in the regions potentially in Bill's path are urged to track the storm's progress over coming days and review emergency plans.