Bill weakens, but still generating huge waves

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

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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

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Little over a month to go and chance for Texas getting a major is over! time keep on ticking, ticking into the fuuuuuuture
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Quoting WINDSMURF:
Its a good thing that there is nothing in the pipeline for the next 7 days I will be going on vacation on sunday and will be out for 2 weeks. I live in Miami. I do not want to sound like JFV/weatherstudent, But should I put up my shutters just in case?


My neighbor left for two weeks and he puts up the back and hard to reach shutters just in case. If his son isn't able to, I'll put up the easy few for him if need be. Although I HIGHLY, HIGHLY doubt that he will need them. The quick forming T.S.'s you usually do not have enough time to put them up anyways...

So, in a nutshell - might not be abad idea to put up the hard ones or the back side of the house ones just in case. Another neighbor who is out alot has accordians so that anyone can put up his shutters in less than 15 minutes. (just a thought)

I have impact doors and windows so my "shutters" are always up!
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112. jpsb
Yea, it is being eroded on the east and the west. But even if it hangs in there I don't see any steering to take bill south. Bill wants to go north and it's got a lot of north momentum, so it would take something really big to push bill south.
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Florida here also. I'm more interested in hearing from people that DO know what they're talking about. And FYI, I emailed a buddy who has relations in N.Scotia and another who lives in New Foundland. So yeah, I worry about everywhere else these over-sized tornado's hit.
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Quoting leftovers:
saving the characters energy.


You may be right...how have YOU been, by the way?
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@104, even in it's current state that high is not very strong. Doesn't even show up on the upper-air maps, it's only at 850 mb and below. That's why I'm very confident that the combined effects of Bill and an unseasonably strong trough will have no trouble breaking it down.
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Quoting WINDSMURF:
Its a good thing that there is nothing in the pipeline for the next 7 days I will be going on vacation on sunday and will be out for 2 weeks. I live in Miami. I do not want to sound like JFV/weatherstudent, But should I put up my shutters just in case?


CMC wants to kick something up off of CV next week.
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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 guess we are going to go back into a slow period?
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Quoting StonedCrab:


Florida is still here.
It's just that many of us don't find it necessary to wishcast, or to comment on bogus wishcasts.


hopefully no more of that the rest of the season. i think you may luck out
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Quoting Crawls:


I agree 100%.


Yep. Now we know who the culprits are, all those folks from Florida to Texas! ;)
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Quoting rwdobson:
That high is going to be broken down by the trough, so Bill won't be getting squished under it. If you look at the models, it basically disappears, leaving the stronger part of the bermuda/azores high to the east intact.


Those are JUST models. It has not happened yet. We are just playing the what if thing.
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Thank you Dr. M
11 am Update:



My 11 am Projected Path:


Ill be posting my 2nd ever blog in a bit.
Member Since: June 29, 2009 Posts: 13 Comments: 5238
I am going to ask an odd question. If all of warnings for the USA is put out by the NHC, why would other very known weather websites include most of southern NE in their cone? Why not go along with what the NHC is putting out? What are they looking at differently? I don't get it.
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Quoting KEHCharleston:
I agree, that it is much quieter this morning. I am finding the blog informative and interesting.

I for one do not miss the disrespect, wild forecasting and trolling.


I agree 100%.
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Bill is a lot closer to St. Croix now. We should see a vortex message from the HH in a little over an hour.
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Quoting DestinJeff:


Looks to have progressed as far as the Cumberland Plateau of TN. How far east does it really need to be before winds out in front will induce steering for Bill?


That Trough needs to get near the East coast to make Bill turn more NORTH AND especially toward the NE.
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Quoting AussieStorm:

I watched the Braves this morning, didn't see the end, went for a walk in the beautiful Sydney sunshine.


We have a member of your fine country on our team and having a pretty good year too. However, I am sure you are aware of that already. BTW 15-2 Braves.
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That high is going to be broken down by the trough, so Bill won't be getting squished under it. If you look at the models, it basically disappears, leaving the stronger part of the bermuda/azores high to the east intact.
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Quoting funeeeg:
Hello, long time weather watcher and cloud spotter, my family think I am a geek but that's by the by. Interesting visible imagery of Bill shows ARC clouds on the western boundary. I always thought ARC clouds were an indication of cyclone that is mixing out dry air, do you think that this is the case with Bill? Just an observation that is probably irrelevant here.


I see some of that, but I'm a sideshow watcher too, no pro...
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95. jpsb
Quoting TampaSpin:


I posted in the Old blog that it appeared the trough was flattneing out some in the last few frames and riding up an over the High parked over the East coast. It need to keep coming! You can see what im talking about in this Water Vapor Loop.
Yea, I noticed that yesterday too. But the trof should be far enough east to protect the usa tomorrow and Bill's still got that short wave trof right in front of him to deal with so hopefully the forecast is good as far as the usa is concerned. Now Canada really needs the big trof to help them out. I'm not convinced they are going to get the help they need.
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Quoting BajaALemt:
Hey NE? You hear from bone?


No,Baja,haven't seen him in quite a while,may have problems again connecting,I would have thought he would have shown up with the tropic season.
Member Since: September 6, 2007 Posts: 862 Comments: 15056
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.
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Quoting mkmand:

Half of them are all wish-casters. The other Half are from Florida. Both groups don't believe Bill is worth keeping up with anymore, apparently!


Florida is still here.
It's just that many of us don't find it necessary to wishcast, or to comment on bogus wishcasts.
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Quoting nrtiwlnvragn:


School has started in some areas, at least in some areas of South Florida.


That having been said, while most of us in here are very circumspect in their postings (I said most...LOL) remember that there are schools that lurk here; whole classrooms of earthscience students hanging on our every word...LOL

Kind of sobering and makes me want to look over my shoulder...
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Quoting DestinJeff:


i think that strengthening high to Bill's NW will actually aid in him squeezing north on the eastern flank of it ... to follow the weakness between the FL high and the mid-atlantic ocean high.

however, if Bill manages to get squished "under" the high then that would be a different (and not at all expected) story



Jeff you are 100% correct....could not have said it better.....That is exactly the other case to be made with Bill as i have been saying as the other possilbe track. Not likely but, just something that is always a possbility
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Quoting WINDSMURF:
Its a good thing that there is nothing in the pipeline for the next 7 days I will be going on vacation on sunday and will be out for 2 weeks. I live in Miami. I do not want to sound like JFV/weatherstudent, But should I put up my shutters just in case?


Or canesrule1...



Some activity out there.

Considering how fast Claudette formed, maybe you should at least put them in an accessible place :)
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Quoting IKE:


Part of it is school(thank God)....another part is it looks like Bill is going to go east of the USA....



Thank goodness the kids are back in school. I can actually lurk now and find good discussion!
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Quoting mkmand:

Half of them are all wish-casters. The other Half are from Florida. Both groups don't believe Bill is worth keeping up with anymore, apparently!



Some of us have to work, LoL
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((( DL ))) Mornin, hun!

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Quoting scott1968:


I remember a time when I could say "Go Braves" boy those were the good ole days. Have fun in the post season!

I watched the Braves this morning, didn't see the end, went for a walk in the beautiful Sydney sunshine.
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I agree, that it is much quieter this morning. I am finding the blog informative and interesting.

I for one do not miss the disrespect, wild forecasting and trolling.
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Hello, long time weather watcher and cloud spotter, my family think I am a geek but that's by the by. Interesting visible imagery of Bill shows ARC clouds on the western boundary. I always thought ARC clouds were an indication of cyclone that is mixing out dry air, do you think that this is the case with Bill? Just an observation that is probably irrelevant here.
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Quoting leftovers:
seen better surf
storms bill is moving too quickly


This morning's cameras show a smallish La Ocho with at least 4-6' Jobos. Not the doomsday 7 feet 16 second swell that was predicted.

Seems I'm going to finish my Ellipses precalculus homework after all.

Quoting scott1968:


I remember a time when I could say "Go Braves" boy those were the good ole days. Have fun in the post season!


Me too... oh, the 90's.
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Its a good thing that there is nothing in the pipeline for the next 7 days I will be going on vacation on sunday and will be out for 2 weeks. I live in Miami. I do not want to sound like JFV/weatherstudent, But should I put up my shutters just in case?
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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


this part makes me nervous
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Quoting IKE:


Part of it is school(thank God)....another part is it looks like Bill is going to go east of the USA....



Kids post on here? Never would have guessed that. [sarcasm off]
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#65

interesting destin, thanks
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Quoting BajaALemt:
Hey NE? You hear from bone?


I bet BoneDog will be popping in very shortly....with Bill coming
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Will the SST Bill's heading towards result in rapid intensification?
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73. IKE
Quoting Crawls:
It's really quiet in here this morning. I wonder where everyone is?


Part of it is school(thank God)....another part is it looks like Bill is going to go east of the USA....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Morning All! Hey Flood & Baja!

I hope that predicted trough moves in on time. Bill would take aim at some highly populated areas if it doesn't.
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Quoting Crawls:
It's really quiet in here this morning. I wonder where everyone is?

Half of them are all wish-casters. The other Half are from Florida. Both groups don't believe Bill is worth keeping up with anymore, apparently!
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Similar to the GFS 925 hPa Wind Swath fields, I also generate the ensemble wind swaths from the GFS coarser grids provided by NCEP (1 degree). You can clearly see the impact of the initialization at the earlier points of Bill's track.

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Quoting DestinJeff:


no problem ... never know when somebody will have that issue. it sucks.

i know you were exploring some different solutions, especially regarding the GOM high moving NE ahead of the front yesterday. thoughts today? that trough does look potent.


I posted in the Old blog that it appeared the trough was flattneing out some in the last few frames and riding up an over the High parked over the East coast. It need to keep coming! You can see what im talking about in this Water Vapor Loop.
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Quoting rwdobson:
@50, that steering you are seeing is going to be pushed away by the trough coming east.


you mean it will push the whole thing east?
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Hey NE? You hear from bone?
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Quoting Category5hitsNewYork:

We don't have to! Go Yankees!


I remember a time when I could say "Go Braves" boy those were the good ole days. Have fun in the post season!
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I always think it's a trip how, when a system is no longer a threat to Florida, the blog quiets down.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.