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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the weather network says bill will make landfall in nova scotia on sunday as a category 1 or 2
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2210. divdog
Quoting DR1791:


lol.. Pros are wrong most of the time to!
pros are right most of the time especially the nhc
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g/m all...i'm a daily reader of the blogs here and enjoy all the info e1 has to share.
I esp like cajunmoma and nishinigami cause I can tell ya both from LA. (Gretna, LA here)
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Morning all...

Hoping for some wisdom here. I live in southern costal Maine, yet every local forecaster (don't even get me started on these nimrods... my cats could make more accurate forecasts) are predicting no wave action, little to no wind, and "some" rain? Really?

Given the monster that will be wandering past off shore, and assuming the NHC projected track... this can't possiblely be correct, can it? Coastal Maine gets nothing but worthless piles of Home Depot receipts and throngs of confused French Canadians?

Not hoping for the wrath of god.... just befuddled by the reporting of lack of any weather action.

And um... GO SOX.
2207. Grothar
Anyone, Anyone.

Just lurking this morning and trying to catch up. There was mention of a system possibly developing off the Bahamas next week and the obvious feature emerging off the coast of Africa. Question: Are these two separate systems they are mentioning in the blog, or is it the wave that if off of Africa.
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Thank you Sullivan. Look forward to the guide.
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2204. IKE
NEW BLOG!
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GOES-East will be in Rapid Scan Operations mode today. Increased frequency of images are available at the NASA GHCC site.

Bill GHCC loop
Member Since: September 23, 2005 Posts: 14 Comments: 11307
Quoting WxLogic:
I've find it interesting how the blog works... depending on the region where a tropical disturbance might affect... you see different "swat" teams... in which basically if the SE is to be affected the the FL crew coming on board... if the C GOM is targeted then the LA crew jumps in... etc... I find it quite an interesting and amusing behavior. Keep in mind that posting a lot tends to drain you even though you're not doing no physical activity... just a lot of mental work (sometimes)... lol.

GOM S.W.A.T. here! Always ready with the cold beer and Zatarains!
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Quoting WxLogic:
I've find it interesting how the blog works... depending on the region where a tropical disturbance might affect... you see different "swat" teams... in which basically if the SE is to be affected the the FL crew coming on board... if the C GOM is targeted then the LA crew jumps in... etc... I find it quite an interesting and amusing behavior. Keep in mind that posting a lot tends to drain you even though you're not doing no physical activity... just a lot of mental work (sometimes)... lol.


Those are the "only if it's coming here", "ones that want it to come there" and "the morons that get their jollies picking the behavior".

It's kind of like a hurricane coming through the blog, ironic.
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Quoting Herbertsbox:
Thanks all. Much to learn, but willing to put in the time.

BTW, can anyone recommend any good books to firmly grasp some basic fundamentals of meteorology?



I think your best place to start would be AMS journals. All editions up to 2003 (I believe) are free on the internet and contain a wealth of research information.
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2197. breald
Quoting hurricanehanna:

North or South? They are separate states you know. :)


In more ways than just their name...LOL.
Member Since: May 28, 2008 Posts: 38 Comments: 5303
Quoting presslord:


Big ol' fat ugly mother?

STOP IT! rofl...I now have coffee on the computer monitor! :)
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Thanks all. Much to learn, but willing to put in the time.

BTW, can anyone recommend any good books to firmly grasp some basic fundamentals of meteorology?
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Quoting P451:


When did this happen? I refuse to believe it.

There is one coastline and it is the Carolina coastline. All other coastlines are inferior.

Anyone who disagrees has to answer to Presslord.


Nope - need to distinguish between North and South Caroline as Press has said many many times.....it's not "the Carolinas"....but it is a beautiful coastline!
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Quoting SQUAWK:


Thats Carolina for "both of them," but you knew that already, didn't you!!



Ah! Of course!!! Bofe-uv-'em...Both of them...perfect...
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2191. SQUAWK
Quoting presslord:


Big ol' fat ugly mother?


Thats Carolina for "both of them," but you knew that already, didn't you!!
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Cape Verde Live Cam

Shown below is a still shot, for Live Cam go to the link above.

16°54′00″N 24°59′00″W - Mindelo Harbor, (North side of Sao Vincete, Cape Verde)


Member Since: August 19, 2008 Posts: 6 Comments: 2490
Quoting presslord:


On behalf of JFVWS: So...You're saying it's definitely gonna hit SEFLA as a category 5?

ROFL . Made my morning! Thanks press
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2188. WxLogic
I've find it interesting how the blog works... depending on the region where a tropical disturbance might affect... you see different "swat" teams... in which basically if the SE is to be affected the the FL crew coming on board... if the C GOM is targeted then the LA crew jumps in... etc... I find it quite an interesting and amusing behavior. Keep in mind that posting a lot tends to drain you even though you're not doing no physical activity... just a lot of mental work (sometimes)... lol.
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2187. DR1791
Quoting watcher123:
Looks like the pros nailed this one.

Pros vs Joes
Pros 1
Joes 0

---
What is that at about 12N and 32W? Looks like a possible D storm later?


lol.. Pros are wrong most of the time to!
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Quoting SQUAWK:


bofum


Big ol' fat ugly mother?
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Quoting CloudGatherer:


CIMSS has switched off the weakening flag, after a day of steady declines, and the ADT model shows some modest strengthening. It'll be good to get some actual data from the storm.


Satellite appearance would indicate a Cat 2.
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2183. hydrus
Quoting Weather456:


I'm actually more afraid that my car insurance might expire before I can pay.
lol..
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2182. SQUAWK
Quoting hurricanehanna:

North or South? They are separate states you know. :)


bofum
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Wow, slow morning! Does anyone know how close Bill's eye is supposed to pass to Bermuda? Are they likely to get TS force winds, or just rain and waves? In local news, I saw the most beautiful rain clouds/sunrise in SE Texas this morning, which is a good way to make up for the 111 heat index we should have this afternoon. Blech!
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Quoting P451:


Nope, the Carolinas.


*runs*

North or South? They are separate states you know. :)
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2177. SQUAWK
Quoting presslord:


On behalf of JFVWS: So...You're saying it's definitely gonna hit SEFLA as a category 5?


No Press, most likely to hit the Carolinas!(Not running!!
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2176. WxLogic
Quoting presslord:


On behalf of JFVWS: So...You're saying it's definitely gonna hit SEFLA as a category 5?


Becareful... he might be wishcasted into the Blog... hehe...
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Quoting P451:


Nope, the Carolinas.


*runs*


you'd better run...
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Quoting P451:
Recon on it's way to Bill.


CIMSS has switched off the weakening flag, after a day of steady declines, and the ADT model shows some modest strengthening. It'll be good to get some actual data from the storm.
Member Since: August 18, 2009 Posts: 0 Comments: 460
Quoting presslord:


On behalf of JFVWS: So...You're saying it's definitely gonna hit SEFLA as a category 5?

rofl! what a way to start my morning - always a good laugh Press!

Morning all.
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Quoting weathermanwannabe:
Good Morning. That wave at 30W does look interesting and the model run posted by P451 seems to show a possible path similar to Bill. However, Bill blossomed in the mid-Atlantic so development closer to the Islands would take it a bit more Westward in terms of possible trajectory. Too far out to tell whether it will develop or not but sheer currently remains low if it can stay below 13N on the way towards the Islands....Need to keep an eye on it.


On behalf of JFVWS: So...You're saying it's definitely gonna hit SEFLA as a category 5?
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Quoting canehater1:
Surface map shows 1006mb low over Africa as well ..something to watch...


It is that time of the year over the next 2-3 weeks.... :)
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Quoting weathermanwannabe:
Good Morning. That wave at 30W does look interesting and the model run posted by P451 seems to show a possible path similar to Bill. However, Bill blossomed in the mid-Atlantic so development closer to the Islands would take it a bit more Westward in terms of possible trajectory. Too far out to tell whether it will develop or not but sheer currently remains low if it can stay below 13N on the way towards the Islands....Need to keep an eye on it.
Surface map shows 1006mb low over Africa as well ..something to watch...
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Quoting P451:
Bermuda getting it's first rain.



That is a solid shield of rain.
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Blog very quiet considering we have a major hurricane out there....that IS impacting the US, in terms of rip currents and large waves.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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