Bill batters Bermuda; Canada next

The winds are dying down on Bermuda, which took a glancing blow from Hurricane Bill last night and this morning. Bill's center passed about 170 miles west of the island, bringing top sustained winds at the Bermuda airport of 46 mph, gusting to 60 mph, at 8:55 pm AST last night. One Bermuda weather station at an elevation of 262 ft recorded a wind gust of 95 mph during a severe thunderstorm last night, resulting in some wind damage that will be surveyed today. Hurricane Bill was undergoing an eyewall replacement cycle last night during its passage west of Bermuda, and the collapse of the inner eyewall meant that the hurricane could not strengthen. An outer rain band has now formed into a new, much larger diameter eyewall. As a result, Bill now has a huge, 50-mile diameter eye. Now that the eyewall replacement cycle is complete, Bill has about a 12-hour window of time to intensify, since the hurricane is crossing the axis of the warm Gulf Stream Current, and wind shear is low, 5 - 10 knots.

Around midnight tonight, Bill will lose its warm waters, and SSTs will decline quickly to 19°C (66°F) Sunday morning. By Sunday afternoon, wind shear will rise to 40 knots as Bill encounters the upper-level westerly winds of the large trough of low pressure that is steering the hurricane to the north. These strong upper-level winds will act to turn Bill to the northeast, and shear the hurricane apart. By the time Bill reaches Nova Scotia, Bill should be approaching tropical storm strength, though it will still be generating huge waves.


Figure 1. Visible satellite image of Bill at from Saturday morning 8/22/09.

Bill's waves
Hurricane Bill continues to generate huge waves, thanks to its large size and the long time it spent at major hurricane intensity. This morning, Bill passed 95 miles east of Buoy 41048, which recorded significant wave heights of 27 feet, and sustained winds of 50 mph. Huge waves battered Bermuda yesterday and today, as seen in the wunderphotos taken by denmar, at the bottom of the blog. Output from NOAA's Wavewatch III model suggests that significant wave heights near Bill's center will peak at 40 feet today. Large swells from Bill have reached most of the U.S. East Coast, and wave heights will increase today. Waves at the Nantucket, Massachusetts buoy were up to 9.5 feet this morning, and the Cape Cod Buoy had 8.5' waves. The big waves affecting the U.S. coast will cause very dangerous swimming conditions, and will likely cause several million dollars in beach erosion damage. Though Bill will bring sustained winds near 40 mph and occasional heavy rain showers to southeastern Massachusetts, it is Bill's waves that are the primary threat of the storm to the U.S.

Elsewhere in the tropics
The tropical wave in the middle Atlantic that NHC mentioned in their Tropical Weather Outlook this morning is falling apart, and there are no threat areas in the Atlantic worth mentioning today. Though the models are not calling for any clear-cut development of any tropical cyclones over the next week, we should keep a close eye on the waters between the Bahamas and North Carolina by Wednesday. There could be two triggers for tropical cyclone formation then--the remains of the cold front that will be pushing off the U.S. East Coast this weekend, plus a tropical wave. The Western Caribbean also may be prime for some development late next week, as well as the region off the coast of Africa.

I'll have an update Sunday.

Jeff Masters