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Bill weakens, but still generating huge waves

By: Dr. Jeff Masters , 2:29 PM GMT on August 20, 2009

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


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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Just a question.The loop I was watching shows a samll spin at around 28/72 that appears to heading toward the Bahamas.I know it is probably ULL but what is the pressure in the area and will Bill cause a drop in that pressure or eat the little spinner?? By the way am in SE Fla and not newwavecasting but didn't Claudette start around that area.Someone also mentioned the other little spinner just east of Belize.
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Quoting BajaALemt:
Have you made your preparations, Cape?


"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."

Wondering if this is for the ENTIRE Cape, South Shore or only Chatham and National Seashore. Devasting either and any way. Tourists will flee, economy tank, erosion will be crazy.

I live on the Cape of Cod. I work in Dennis Port at a resort ... here it is:



think of what an 18' wave will do here. South side beach. That's water on the far side, that's the Bay side. This is in Dennis Port somewhat close to the elbow.

I live 15 miles away. Doesn't make me feel any better.
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Quoting scaldisnoel:
HHunter, be careful not to overstate what Joe Bastardi is saying, since there are some serious JB haters in here. My read on what he said in his most recent post is that Providence and Boston are probably out of the woods except for some gale force gusts and some heavy rain, unless Bill tracks more to the west than predicted. The Cape on the other hand, he seems to suggest, is quite likely to see, if not a direct hit, some hurricane force winds. He is more in line with the storm following the west side of the cone, or even a little west of that.


I listened to what he said and he does not sound unreasonable. I kind of like the guy myself.
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Quoting FreelanceHistorian:


What happened last time is that TS force winds directly against the side of the house popped the seams in the paneling under the eaves. The triangle portion above the cinderblock wall and under the roof. The water got inside the cinderblocks, and flowed down, then out into the house from under the baseboards. :(
Geez. Never would have thought of that as a possibility, at least not with the roof still on..... :o(
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For those of you that live way up the East Coast and may not be as acustomed to the recources and info as us GOMEX residents let me give you a little advice...

1. Prepare now, Don't wait until the chaos ensues. Hurricane preparedness checklists are available all over the internet.

2. Trust the "cone of uncertainty" out only 48 hours. Beyond that will continue to remind you of your wiper blades.

3. Do not get too focussed on just the black line. If you are anywhere in the 48 hour "cone of uncertainty" you are at just as much risk as if the little black line was right on top of you.

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THEY WILL CHANGE THE FORCAST AND TRACK OF BILL AT LEAST 10 MORE TIMES OVER THE NEXT 2 DAYS
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Quoting OSUWXGUY:
Good Morning All!

12UTC GFS shift the track back east 50-100 miles as it passes by the Cape...

One thing that should further help the Cape even if it were to get a little closer is that with the strong trough and associated low pressure - the pressure gradient will be considerably weaker on the west side of the storm then the east where strong ridging and high pressure is present.


A trend to the east appears to be shaping up... I believe the presence of shear will not allow Bill to have enough force to fight off the trough.
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It is extremely fortunate that the whole pattern wasn't shifted 200-300 miles further west or the Northeast would have been devastated and Bastardi would be up on his soap box...
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Quoting FreelanceHistorian:


What happened last time is that TS force winds directly against the side of the house popped the seams in the paneling under the eaves. The triangle portion above the cinderblock wall and under the roof. The water got inside the cinderblocks, and flowed down, then out into the house from under the baseboards. :(


That sucks...... :)
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HHunter, be careful not to overstate what Joe Bastardi is saying, since there are some serious JB haters in here. My read on what he said in his most recent post is that Providence and Boston are probably out of the woods except for some gale force gusts and some heavy rain, unless Bill tracks more to the west than predicted. The Cape on the other hand, he seems to suggest, is quite likely to see, if not a direct hit, some hurricane force winds. He is more in line with the storm following the west side of the cone, or even a little west of that.
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Quoting gordydunnot:
I'll be happy when Bill gets north of 26n on his present heading. I believe that will firmly have him in the grasp of the trough and accelerating.
Hear hear. Except 30N would make me happier.
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Quoting DestinJeff:


spinning the wrong way ... AustraliaCaster in that gif?


It's an optical delusion!
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Quoting IKE:


Scrub that question....it's caneluver's model.

School hasn't started back in NC yet?


haha!
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Quoting DestinJeff:


spinning the wrong way ... AustraliaCaster in that gif?

LOL
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Good Morning All!

12UTC GFS shifts the track back east 50-100 miles as it passes by the Cape...

One thing that should further help the Cape even if it were to get a little closer is that with the strong trough and associated low pressure - the pressure gradient will be considerably weaker on the west side of the storm then the east where strong ridging and high pressure is present.
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196. IKE
Quoting IKE:


What models?


Scrub that question....it's caneluver's model.

School hasn't started back in NC yet?
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New gfs 12z develope the tropical wave south of the cape verde islands in the central atlatic at 120 hours.
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No nothing yet, it's a little early to strat worrying about it. I'll watch for another day or two, then make some decisions.
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Quoting FreelanceHistorian:
I love that animated weathercaster, Dan!

I'm glad Claudette didn't form any closer to Tampa. I have to replace some bad T111 on the side of the house, and don't have the money for it right now. Getting water intrusions through the inside of a cinder block wall is NO fun.


I had some flood damage in the basement after TS Francis last year and the contractors "brushed on" a waterproof film on the cinder block which has stopped water intrusion into the basement....Not expensive from Home Depot and a good temporary to permmanent fix.
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12Z GFS... possible Danny and Erika cruising slowly through the C ATL.
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Current forecast for 2000 Fri night. Front (trough) should be off the coast by Sat morning.

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Have you made your preparations, Cape?
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183. IKE
Quoting caneluver:
Models have taken a sharp turn to the west!! OMG


What models?
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It looks like Bill most likely will become a Cat. 4 again. IMO, Bill might hit or brush by Mass. and Maine.

Also, I think the wave near Cape Verde should be watched. It has a surface low and some good vorcity. It needs more convection though.
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The CHC says it's gonna pass right over my head here on the east coast of Nova Scotia.
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ROFL! Now THERE'S a 'westcast'...
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Quoting rwdobson:
Weather in the upper levels of the atmosphere, has a waveform pattern...a series of highs (ridges) and lows (troughs). Like all waveform patterns, it can be described in terms of amplitude and wavelength.


Interesting. Thanks.
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#175
Best one yet!
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Morning. If Bill does end up threading the needle between the US and Bermuda as forceasted by the NHC track, and he is currently moving right along the forecast points, they will get huge Kudos from me on this one....Amazingly great work from them on this one so far.
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HH first hits hurricane force winds about 50 miles out on the SW to W of the eye.
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Quoting StSimonsIslandGAGuy:
Wow tropics chat really is talking about a GA/FL landfall and the trough stalling and I don't know what all. Crazy stuff :)


Sounds like a good reason not to waste any time in there.

wishcasters
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Quoting TexasHurricane:
So, we have had 3 named storms this year. (Ana,Bill and Claudette) How many total do you think we will have this year?


11 likely.
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Quoting FreelanceHistorian:
wow, did most of the board get a "time out" for shennanigans last night? Sure is slow here today.


without a threat to the GOM or Florida then the blog is usually quite since most of the blogger live along the GOM
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Quoting caneluver:
Models have taken a sharp turn to the west!! OMG



Exactly which models are you referring to?
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bastardi...is saying watch out new england...he feels the models are still to far east. He prefers to look at analogs of past similar east coast storms and sees evidence that based on waypoints in track currently hit that this could be like some of the great east coast storms. If it goes a little further west than anticipated even mass. I think it's prudent to get moderately prepared like you would for any storm north easter etc if your on Coastal mass and new england and to be ready for more response if warranted...
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Quoting BajaALemt:
I always think it's a trip how, when a system is no longer a threat to Florida, the blog quiets down.
Morning ya'll.

Seriously, some of the peace and quiet is from all the Caribbean people who are sleeping for the first time this week....lol

But yah, a lot of FL schoolies had to hit the halls of learning (some of them did it literally) this week......

I watched bill pretty heay this week, but I think I can go out and enjoy my last 2 days off, now. Just need some occationsal checks around NHC update times to make sure I'm keeping the "pressure" on. . . . .
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Weather in the upper levels of the atmosphere, has a waveform pattern...a series of highs (ridges) and lows (troughs). Like all waveform patterns, it can be described in terms of amplitude and wavelength.
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Quoting TexasHurricane:
So, we have had 3 named storms this year. (Ana,Bill and Claudette) How many total do you think we will have this year?
Probably won't matter if the "below average" season pans out correctly. Bill is writing the history of the "0-0-0" 2009 season already on its own. This is a terrible threat and will damage all along the conUS coast no matter how its turns or stays where within the cone. The wave action and erosion is a big deal, a very, very big deal, in this part of the world. We're blasted by nor'easters all the time. The waves of a big cane are potentially devastating. It could be another 1944.
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Quoting popartpete:
I fear it, and a pass-by of Bill anywhere closer than 150 miles...Hurricane winds 105 miles out, TS 260 miles out. Jersey Shore here. I think we in for epic water action unlike most of our locals lifetimes.


Bill will have to do some serious strengthening to get to that windfield size. In the southwest quadrant the HH is seeing weak TS strength winds about 150 miles out.
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Quoting caneluver:
Models have taken a sharp turn to the west!! OMG


ummmmm...no
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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather

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