Bill weakens, but still generating huge waves
Hurricane Bill has peaked in intensity, and now shows signs of weakening. Visible and infrared satellite imagery show that the hurricane is no longer as symmetric as it once was, with an oval instead of circular shape to its cloud pattern. Upper-level cirrus clouds are restricted on the storm's southwest side, indicating that upper-level winds from the southwest are shearing the storm. The University of Wisconsin CIMSS wind shear analysis shows about 10 - 15 knots of wind shear impacting Bill. The latest 8:18am EDT eye report from the Hurricane Hunters indicated that the eyewall had a gap in its southwest side, and the pressure had risen 2 mb since last night, to 951 mb. Maximum winds at the surface observed by the SFMR instrument were only Category 2 strength, though winds measured at the aircraft flight level of 10,000 feet still suggested Bill may be a Category 3 hurricane.
Wind shear is forecast to remain low to moderate, 5 - 15 knots, for the next three days, and it is possible Bill may see a relaxation of the wind shear affecting it, allowing re-intensification to Category 4 status. Sea Surface Temperatures (SSTs) will be plenty warm over the next three days, as Bill traverses a region of ocean with SSTs of 28 - 29°C. Total ocean heat content is at a maximum today, and will gradually decline over the next three days.
Figure 1. Visible satellite image of Bill at 1:33 pm EDT Thursday 8/20/09. Bill had an oval shape oriented SW - NE, and was missing upper-level cirrus clouds on the southwest side, indicating that wind shear from strong upper-level southwesterly winds was affecting it.
Water vapor satellite loops continue to show two small "short-wave" troughs of low pressure to the northwest of Bill, and these troughs are continuing to steer Bill to the northwest. The short wave troughs (so called because they have a relatively small amplitude and wavelength) are not strong enough to turn Bill due north, so Bill is expected to miss Bermuda. The official NHC forecast has the radius of tropical storm force winds from Bill barely reaching Bermuda on Saturday, so the island can expect sustained winds in the 35 - 45 mph range for a few hours on Saturday if the hurricane follows the NHC forecast track.
Figure 2. Visible satellite image of Bill's eye zoomed in, taken from NASA's Aqua spacecraft at 10:15am EDT Wednesday August 19, 2009. Image credit: NASA GSFC.
An unusually strong "long wave" trough of low pressure (called long wave because of its large amplitude and wavelength) is expected to develop along the U.S. East Coast this weekend. This trough will turn Bill to the north, and also bring high levels of wind shear in the 40 - 65 knot range on Sunday. The models have moved the forecast landfall point of Bill several hundred miles back and forth to the east and west over the past few days, but mostly agree that Cape Cod and Maine will probably miss a direct hit by Bill. However, these regions are still at the edge of Bill's cone of uncertainty, and a direct strike by Bill at Category 1 or 2 strength is a possibility. However, it is more likely that Bill will come ashore over the Canadian provinces of Nova Scotia or Newfoundland. Bill will be weakening rapidly as it makes landfall, and is likely to be a Category 1 hurricane if it hits Nova Scotia, or strong tropical storm if it hits Newfoundland. If Bill follows the official NHC forecast path, winds on Cape Cod and in eastern Maine are likely to remain below tropical storm force (below 39 mph).
Bill's waves
Hurricane Bill is generating huge waves, thanks to its enormous size and major hurricane intensity. Bill passed about 75 miles southwest of Buoy 41044 this morning, and the buoy recorded sustained winds of 67 mph, gusting to 92 mph, with a significant wave height (the height of the average 1/3 highest waves) of 38.8 feet. Output from NOAA's Wavewatch III model suggests that significant wave heights near Bill's center will peak at 50 feet by Saturday. Large swells from Bill will reach Bermuda this afternoon, increasing seas to 5 - 9 feet, according to the Bermuda Weather Service. Seas will increase to 10 - 20 feet on Friday and 20 - 30 feet on Saturday as Bill makes its closest approach to the island.
In the U.S., Bill's swells will reach New York's Long Island on Friday afternoon, and seas will build to 7 - 10' on Saturday and 12 - 16' on Sunday in the near shore waters. By Friday night, Bill's swells will be affecting the entire U.S. East Coast from Florida to Cape Cod. Maximum sea heights in near shore waters over the weekend will be about 7' from Florida to South Carolina, 11 - 14' along the North Carolina coast, 8 - 11' along the mid-Atlantic coast, and 10 - 11' along the coast of Maine. The highest waves along the U.S. coast will occur at Cape Cod, Massachusetts, where waves of 18 - 23' are being forecast by NOAA for Sunday. Bill's high waves are going to cause millions of dollars in erosion damage and create very dangerous rip currents and swimming conditions along the coast.
Hurricane History of Canada
Canada is no stranger to hurricanes, and receives a hit by a Category 1 or stronger hurricane several times per decade, on average. The most recent hurricane strike on Canada occurred in 2008, when Hurricane Kyle struck the southwestern tip of Nova Scotia, just north of Yarmouth. Kyle was rated a Category 1 hurricane with 75 mph winds at landfall, but damage was limited to uprooted trees, scattered power outages, and minor street flooding in Shelburne. The other hurricane to hit Nova Scotia this decade was much more serious. In 2003, Hurricane Juan made landfall at Halifax, Nova Scotia, as a Category 2 hurricane with 100 mph winds. A record storm surge of 4.9 feet inundated the city's waterfront, resulting in extensive flooding of the Halifax and Dartmouth waterfront properties. A buoy just outside Halifax Harbor measured a significant wave height of 9 meters (30 feet), and maximum wave heights of 20 meters (65 feet). Four people died in the storm. Juan downed a phenomenal number of trees--agriculture specialists estimate that 50 - 100 million trees blew down in Nova Scotia in two hours, with one million downed in Halifax alone. The Canadian Hurricane Center has a nice historical hurricane page with more information and photos.
Figure 3. Close up view of the damage at the Bedford Yacht Club after Hurricane Juan in 2003. Photo: Gary Dunbrack. Image credit: Environment Canada website on Hurricane Juan.
Elsewhere in the tropics
There are no threat areas in the Atlantic worth mentioning today, and no reliable models are calling for tropical cyclone development over the next seven days.
I'll have an update Friday morning.
Jeff Masters
Reader Comments
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Reflector site for those at work, which includes Weather456, daily update.
Bill
Bill
AOI
That site will not let you hotlink images or link to the image. You can only link to the main page.
21/1200 UTC 13.7N 133.0W T2.0/2.0 92E -- East Pacific
Canadian Hurricane Centre still says too early for warnings.
Next AOI
The Twave with persistent area of low pressure near 30W continues to look like a threat to develop. Quikscat this morning maintains this feature quite well and convection has improved significantly since I first started paying attention to this wave two days ago. In fact, on Wednesday there was virtually no convection with it at all.
It is a slow mover which will also work in it's favour.
I can see more and more sites doing that, since the hotlinking uses up bandwidth. One of the FSU sites (AC Evens I think) also will not allow hotlinking.
True, but the wave behind it does not have much in the way of vorticity whereas the one near 30 shows up nicely on the 850 mb vorticity map for the area off the coast of Africa
An interesting little bugger at 30W. Convection has increased, and it does have some 850 mb vorticity. If current trends continue, The NHC should mention it at 2.
Could go "yellow" soon IMO
Just got off the phone with him and he reports that he has got the the Xtrememe Cam up and running from his hotel room in Bermuda. He'll be out all day gathering HD footage so the webcam is a static shot with an audio feed from their local weather office. Check it out at:
Xtremehurricanes.com
Have a nice morning everyone.
That is my thinking as well, kman. Also looks like this will mostly go W to WNW because it would appear the trough would not pick this one up.
Thanks for the update, have a great day!
Flat as a pancake here in Jupiter
I will be closely monitoring a tropical wave over the eastern Atlantic near 29 West Longitude this weekend as quite a few of the computer forecast models indicate that tropical cyclone development may occur east of the Bahamas around the middle to later part of next week. What is interesting is that the GFDL model which was run on Hurricane Bill was able to pick up on this possible development in 5 days. So, currently wind shear is running at around 10 knots around this system, however, it is expected to encounter stronger shear late this weekend into early next week. I agree with the overall model guidance and I think the best chance for development will be in the western Atlantic east of the Bahamas. This is hinted by the GFS model and strongly hinted at by the European, UKMET and Canadian model. I still think that the Canadian model is developing this system too early and too strongly and it will be discounted. That said, the consistency of the European, UKMET and Canadian models in developing a tropical system in about 5 to 7 days east of the Bahamas near 70 West Longitude should not be ignored and I would say it is something we really will have to keep a close eye on once we get into next week.
Seeing some buzz about a possible disturbance approaching SFL next weekend.
12N is not that far north. Plus, this storm is still weak and heading westward.
Thanks in advance
Yes....it is too early to tell where it is going to go.
See post 2134 - If this holds true and it does not develop until it gets pretty far west, then it will have more potential to be a threat. Just have to wait and see.
A lot will depend on what happens with this stalled front. If something develops in the GOM it would most likely amplify the trough and keep the B/A High weak.
What would develop in the GOM???
POSSIBLE GULF COAST SHOWERS AND STRONGER COMNVECTION MAY BE
TRIGGERED BY A POTENTIAL RESIDUAL MID LEVEL LOW THAT MAY BREAK OFF
FROM THE MEAN ERN CONUS TROF WED-THURS. EWD A TROPICAL WAVE
CURRENTLY SW OF THE CAPE VERDE ISLANDS MAY APPROACH THE BAHAMAS
THURSDAY WITH SHOWERS POSSIBLY REACHING FL BY FRIDAY. CMC CONTS TO
BE VERY AGRESSIVE WITH THIS WAVE WHILE ECMWF ENSEMBLES SHOW A
STRONG CLUSTERING OF LOWS IN THIS REGION LATE WEEK. CHI VERTICAL
VELOCITY POTENTIAL CHARTS STRONGLY FAVOR THE TROPICAL EPAC FOR
DEVELOPMENT THIS PERIOD WITH SOME LESSER BUT STILL FAVORABLE
CONDITIONS OVER THE CARRIBEAN/GLFMEX AND BAHAMAS REGION.
Looks unlikely based on the latest models.
Stalled front in the GOM in August, need I say more. Trough split possible.
I picture Bill as being like a giant "Scrubbing Bubbles" sponge or something, heh.
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