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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Blog update (my second ever blog)

Comments appreciated for those who have not read.
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Quoting Ameister12:
Bill looking more and more like a cat 4 again.


Agreed. That 2PM update was mostly worthless - the graphic simply updated the current position of the storm, leaving the track entirely unaltered, and they held the intensity steady, even though newer data shows surface winds back up to 110kts. The aircraft is making another run at the center, and I fully expect the pressure to have dropped back down. The lowest extrapolated reading will probably come in around 947mb, and the Vortex Message in the 949-50 range.
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Quoting pearlandaggie:

OMG!!!!!!!!!!!!!!!!!!!! There extrap takes Bill straight for the "Carolina" line!!!!!!!!!!!!
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Quoting caneluver:
I think it is safe to say that the East Coast will be hurricane free this year. Looks like storms will follow Bill's path.


That's a pretty amazing and dangerous statement; got anything to back it up?
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Bill appears to be restrengthening. Eye widening, becoming cloud free. Signs of a strengthening storm.
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357. bcn
Quoting PcolaDan:


Add this to it and Iceland and UK could be in for some ugly weather down the road.



Yes, Iceland QuikScat is even worst:



in fact, same "color" than Bill ;-)

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Quoting rwdobson:


Umm, safe to speculate maybe. But it's not 100% safe to say the east coast will be hurricane free this week, let alone all season.


Just ignore that troll
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Quoting Floodman:
Conch, the policeman, LOL...how you doing, man?


Hey Flood...I...am doing everything I can to become a millionair by developing custom camo wife beaters...
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Quoting reedzone:
Ok to clear all this east of forecast point stuff.. The center of a Hurricane is normally on the southern part of the eye. Sometimes just south of the eye. So it's right on track, not slightly east or west. The NHC is nailing it so far.


I agree that the NHC's forecasts of this storm have been superlative, but this is the official NHC definition of a "Center":
Center:
Generally speaking, the vertical axis of a tropical cyclone, usually defined by the location of minimum wind or minimum pressure. The cyclone center position can vary with altitude. In advisory products, refers to the center position at the surface.
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Quoting iluvjess:
Funny Pcola... I'm right down the road from you. Baldwin County. Crazy how some of the folks on here that contribute some of the best info are so quick to start the name calling if they do not agree with your opinion. Anyway. Looks like our neck of the woods may have an easy year this year. I hope!


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Quoting caneluver:
I think it is safe to say that the East Coast will be hurricane free this year. Looks like storms will follow Bill's path.


Umm, safe to speculate maybe. But it's not 100% safe to say the east coast will be hurricane free this week, let alone all season.
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Quoting WxLogic:
12Z NOGAPS hinting towards some organized disturb region developing in the W Carib sea. The indication are subtle so don't expect to see a fully fledged system. Will be interesting to see if it continues on subsequent runs and if other models join in.


I know a model yesterday had something coming up from the Caribbean and into the GOM as a developed storm.
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349. bcn
Quoting KEHCharleston:
Has anyone heard from Cotillion lately?


Sorry, unable to translate your comment.
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Bill looking more and more like a cat 4 again.
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346. Skyepony (Mod)
Thanks Hurricane Junky. Was hoping to get to see some wave video. I bet we are in for a treat of wave pics from WuPhotos. Best we enjoy. Erosion is going to bad with Bill.
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Quoting Floodman:


I'm firmly convinced that if there's an NE hit Bastardi's head will explode


If we get hit,and I'll help his head explode
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ok I say it every year cycloneoz is crazy, lol
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Quoting reedzone:
Ok to clear all this east of forecast point stuff.. The center of a Hurricane is normally on the southern part of the eye. Sometimes just south of the eye. So it's right on track, not slightly east or west. The NHC is nailing it so far.
I never knew exactly the center of the storm was. I always figured somewhere in the middle of the eye. Huge gaps in what I know about the basics of these storms.
I must say, I have been pretty impressed with the predicted path and actual path.

Quoting IpswichWeatherCenter:
No,

FYI - the wind has died down, and hes not just the only brit here.
Fortunately I know where you are ;), it is always a pleasure to read you on the blog.
You and I (and many others) indicate with our handles, where we are located. But I do not have a clue about most people here.
I would love it, if folks gave an indication as to where they are when they post.

I will miss the 5pm (sigh), off to work.
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Conch, the policeman, LOL...how you doing, man?
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Oh, I thought you were referring to our current windy weather but now I saw the images RyanFSU posted showing the remnants of Bill heading towards our islands. Ugh, we could be in for some nasty weather next week. The metoffice doesn't mention anything yet in their 6-15 days outlook. I'll keep an eye on it though.

Hey Floodman. Danke, mir geht's gut. I hope you are ok, too.
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Quoting reedzone:
The center of a Hurricane is normally on the southern part of the eye. Sometimes just south of the eye.


I've never heard that mentioned or even hinted at anywhere before. Do you have any data or links to support that statement?
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thankyou! Someone else acknowledges the facts. Be carefull though! You will be labeled for a comment like that! lol
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taistelutipu, was ist los?

How are you?
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Quoting Skyepony:
Bermuda should at least make for spectacular wave footage from Oz.

hurricanejunky~ Did he say anything about chasing up to Newfoundland or those parts?


Chasing to newfoundland for Bill? I don't think he'll be able to get from Bermuda to there in time to intercept even if he wanted to. His itinery takes him back from Bermuda on Monday and flying back to New Mexico on Tuesday. The wave action should be incredible! They were saying 30-40 waves...
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Funny Pcola... I'm right down the road from you. Baldwin County. Crazy how some of the folks on here that contribute some of the best info are so quick to start the name calling if they do not agree with your opinion. Anyway. Looks like our neck of the woods may have an easy year this year. I hope!
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Quoting rareaire:
whats up flood you enjoying this nice weather?


I'm hoping this trough drops a little further so we can get a little rain...

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000
WTNT33 KNHC 201739
TCPAT3
BULLETIN
HURRICANE BILL INTERMEDIATE ADVISORY NUMBER 21A
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
200 PM AST THU AUG 20 2009

...LARGE HURRICANE BILL RACING NORTHWESTWARD...SPREADING HIGH SWELLS
OVER THE WESTERN ATLANTIC...

A HURRICANE WATCH IS IN EFFECT FOR BERMUDA. A HURRICANE WATCH MEANS
THAT HURRICANE CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...
GENERALLY WITHIN 36 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE OF THE UNITED
STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE.

AT 200 PM AST...1800 UTC...THE EYE OF HURRICANE BILL WAS LOCATED
NEAR LATITUDE 23.2 NORTH...LONGITUDE 62.6 WEST OR ABOUT 645
MILES...1035 KM SOUTH OF BERMUDA.

BILL IS MOVING TOWARD THE NORTHWEST NEAR 18 MPH...30 KM/HR...AND
THIS GENERAL MOTION IS EXPECTED TO CONTINUE TROUGH FRIDAY. ON THIS
FORECAST TRACK...THE CORE OF HURRICANE BILL IS EXPECTED TO PASS
OVER THE OPEN WATERS BETWEEN BERMUDA AND THE EAST COAST OF THE
UNITED STATES EARLY SATURDAY.

MAXIMUM SUSTAINED WINDS REMAIN NEAR 120 MPH...195 KM/HR...WITH
HIGHER GUSTS. BILL IS A CATEGORY THREE HURRICANE ON THE
SAFFIR-SIMPSON SCALE. SOME STRENGTHENING IS FORECAST DURING
THE NEXT 24 HOURS AND BILL COULD REGAIN CATEGORY FOUR STATUS ON
FRIDAY.

BILL IS A LARGE TROPICAL CYCLONE. HURRICANE FORCE WINDS EXTEND
OUTWARD UP TO 105 MILES...165 KM...FROM THE CENTER...AND TROPICAL
STORM FORCE WINDS EXTEND OUTWARD UP TO 260 MILES...415 KM.

THE LATEST MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RESERVE
HURRICANE HUNTER PLANE WAS 951 MB...28.08 INCHES.

LARGE SWELLS GENERATED BY THIS HURRICANE ARE AFFECTING THE NORTHERN
LEEWARD ISLANDS...PUERTO RICO AND HISPANIOLA...AND SHOULD BEGIN
AFFECTING THE BAHAMAS...BERMUDA...MOST OF THE U.S. EAST COAST...AND
THE ATLANTIC MARITIMES OF CANADA DURING THE NEXT FEW DAYS. THESE
SWELLS WILL LIKELY CAUSE EXTREMELY DANGEROUS SURF AND
LIFE-THREATENING RIP CURRENTS. PLEASE CONSULT STATEMENTS ISSUED BY
YOUR LOCAL WEATHER OFFICE FOR MORE DETAILS.

...SUMMARY OF 200 PM AST INFORMATION...
LOCATION...23.2N 62.6W
MAXIMUM SUSTAINED WINDS...120 MPH
PRESENT MOVEMENT...NORTHWEST OR 305 DEGREES AT 18 MPH
MINIMUM CENTRAL PRESSURE...951 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
500 PM AST.

$$
FORECASTER AVILA
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12Z NOGAPS hinting towards some organized disturb region developing in the W Carib sea. The indication are subtle so don't expect to see a fully fledged system. Will be interesting to see if it continues on subsequent runs and if other models join in.
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329. amd
Looks like Bill continues to move just west of a true NW direction.

Bill has moved 0.6 degrees North and 0.9 degrees West in the past 3 hours.

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Re: 304.

No, I haven't heard anything of Cotillon lately. As for the winds I can only speak of the situation at the North Wales coast. We had quite a windy afternoon yesterday with several showers. Today it has been rather sunny but still very windy and some occasional showers. I'll get some wind readings in Wales for you (as Wales normally is windier than England, barring the extreme South-West, i.e. Cornwall. If you are interested in reading more about it, here is the link about the regional climates of the British Isles.).

One PWS in Niwbwrch at the west coast of Anglesey reported gusts of 32 mph earlier today whereas a station run by the UK metoffice in Valley a bit further up north recorded gusts of 50 mph and a 10 min average of 30 mph. The station in Capel Curig in the Snowdonia massive even recorded gusts of 67 mph early this morning and 10 min averages of 45 mph.

Ok, still nothing really compared to Bill but it is tropical storm force after all.
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327. Skyepony (Mod)
Quoting justalurker:
thank you bot reed and scald for your reply..I'll go ahead and proceed with my plans.

btw, i'm new here and wanted to know if any members besides the DR. ever worked in NHC? or a newscaster?


I've forecasted for a few companies & a business I had would have been unsuccessful if I couldn't schedule around the weather a week at a time.
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Quoting iluvjess:
"Don't think you're a wishcaster...you're just making a mountain out of a molehill."

With all due respect, there is nothing "molehillish" about the path of a hurricane sir.


No, but there is something very molehillish about the small, and possibly non-existent, track deviations you are talking about.
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Quoting Floodman:


I'm firmly convinced that if there's an NE hit Bastardi's head will explode


lmao
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whats up flood you enjoying this nice weather?
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HWRF 12Z, GFDL, GFS, NAM: wind swaths



Last 20 HWRF/GFDL Bill forecasts


Link
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321. IKE
Quoting Floodman:


I'm firmly convinced that if there's an NE hit Bastardi's head will explode


LOL.
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My second ever blog (first was yesterday):
Please read and comment! :)
Blog Update
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Quoting KEHCharleston:
Has anyone heard from Cotillion lately?


No,

FYI - the wind has died down, and hes not just the only brit here.
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Quoting OSUWXGUY:
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...


I'm firmly convinced that if there's an NE hit Bastardi's head will explode
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Quoting iluvjess:
It's ok to agree to disagree.


Says you.

Wanna fight?

p.s. j/k
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Time will tell and I hope he hits each and every forecast point. However, if he doesnt turn right fairly soon it appears that he will be getting off track a little to the left.
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315. Skyepony (Mod)
Bermuda should at least make for spectacular wave footage from Oz.

hurricanejunky~ Did he say anything about chasing up to Newfoundland or those parts?
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thank you bot reed and scald for your reply..I'll go ahead and proceed with my plans.

btw, i'm new here and wanted to know if any members besides the DR. ever worked in NHC? or a newscaster?
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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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