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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Bill also appears to be making it's northern turn now. Good on Bill.
...SPECIAL FEATURES...
HURRICANE BILL IS CENTERED NEAR 25.5N 64.9W OR ABOUT 405 NM S OF BERMUDA AND ABOUT 805 NM SE OF CAPE HATTERAS NORTH CAROLINA MOVING NW AT 16 KT. THE LATEST MINIMUM CENTRAL PRESSURE JUST REPORTED BY AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT IS 951 MB. MAXIMUM SUSTAINED WIND SPEED IS 105 KT WITH GUSTS TO 130 KT. SEE THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS TCMAT3/WTNT23 KNHC FOR MORE DETAILS. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM OF THE CENTER IN THE E SEMICIRCLE WITH SCATTERED MODERATE CONVECTION COVERING THE REMAINDER OF THE AREA FROM 23N-29N BETWEEN 58W-63W.
You're from the Maryland side of the Bay?
Eastern Shore?
TCPAT3
BULLETIN
HURRICANE BILL INTERMEDIATE ADVISORY NUMBER 23A...CORRECTED
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
200 AM AST FRI AUG 21 2009
CORRECT DAYS IN MOTION AND INTENSITY PARAGRAPHS...
...BILL WEAKENS SLIGHTLY...STILL HEADING QUICKLY NORTHWEST...
A TROPICAL STORM WARNING AND A HURRICANE WATCH ARE IN EFFECT FOR
BERMUDA. A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM
CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 24
HOURS. A HURRICANE WATCH MEANS THAT HURRICANE CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 36 HOURS.
INTERESTS ALONG THE COAST OF NEW ENGLAND AND IN THE CANADIAN
MARITIMES SHOULD MONITOR THE PROGRESS OF BILL.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA OUTSIDE OF THE UNITED
STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR NATIONAL
METEOROLOGICAL SERVICE. FOR STORM INFORMATION SPECIFIC TO YOUR
AREA IN THE UNITED STATES...INCLUDING POSSIBLE INLAND WATCHES AND
WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL
WEATHER SERVICE FORECAST OFFICE.
AT 200 AM AST...0600 UTC...THE CENTER OF HURRICANE BILL WAS LOCATED
NEAR LATITUDE 25.5 NORTH...LONGITUDE 64.9 WEST OR ABOUT 465 MILES...
750 KM...SOUTH OF BERMUDA AND ABOUT 925 MILES...1490 KM...SOUTHEAST
OF CAPE HATTERAS NORTH CAROLINA.
BILL IS MOVING TOWARD THE NORTHWEST NEAR 18 MPH...30 KM/HR. A
GRADUAL TURN TO THE NORTH-NORTHWEST IS EXPECTED LATER TODAY...
FOLLOWED BY A TURN TOWARD THE NORTH ON SATURDAY. ON THE FORECAST
TRACK...THE CORE OF THE HURRICANE IS EXPECTED TO PASS BETWEEN
BERMUDA AND THE EAST COAST OF THE UNITED STATES ON SATURDAY.
MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 120 MPH...
195 KM/HR...WITH HIGHER GUSTS. BILL IS A CATEGORY THREE HURRICANE
ON THE SAFFIR-SIMPSON SCALE. SOME FLUCTUATIONS IN INTENSITY ARE
LIKELY DURING THE NEXT 12 TO 24 HOURS...AND BILL COULD REGAIN
CATEGORY FOUR STRENGTH LATER TODAY. GRADUAL WEAKENING IS EXPECTED
TO BEGIN ON SATURDAY.
BILL IS A LARGE TROPICAL CYCLONE. HURRICANE FORCE WINDS EXTEND
OUTWARD UP TO 115 MILES...185 KM...FROM THE CENTER...AND TROPICAL
STORM FORCE WINDS EXTEND OUTWARD UP TO 260 MILES...415 KM.
THE LATEST MINIMUM CENTRAL PRESSURE JUST REPORTED BY AN AIR FORCE
RESERVE HURRICANE HUNTER AIRCRAFT IS 951 MB...28.08 INCHES.
BILL IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF 2 TO 4
INCHES OVER BERMUDA...WITH POSSIBLY SOME AMOUNTS OF 6 INCHES.
SIGNIFICANT COASTAL FLOODING IS EXPECTED ALONG PORTIONS OF THE
BERMUDA COASTLINE OVER THE NEXT DAY OR TWO DUE TO LARGE AND
DANGEROUS BREAKING WAVES GENERATED BY BILL.
LARGE SWELLS GENERATED BY THIS HURRICANE ARE AFFECTING PUERTO
RICO...HISPANIOLA...THE BAHAMAS...AND BERMUDA...AND SHOULD BEGIN
AFFECTING MOST OF THE U.S. EAST COAST AND THE ATLANTIC MARITIMES OF
CANADA DURING THE NEXT DAY OR TWO. 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 AM AST INFORMATION...
LOCATION...25.5N 64.9W
MAXIMUM SUSTAINED WINDS...120 MPH
PRESENT MOVEMENT...NORTHWEST OR 310 DEGREES AT 18 MPH
MINIMUM CENTRAL PRESSURE...951 MB
THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL
HURRICANE CENTER AT 500 AM AST.
Given the latest Dvorak presentation this intensity may be generous..will see at next advisory.
And your weather input was?
Thanks for the update Chicklit! I wonder if Bermuda is ready...even if it is just tropical storm force winds?
XFD owned.
Seconded.
I was going to bring up the topic of wind shear, take a look, this maybe is whats affecting Bill, 20-40knts shear:
THIS is hurting Bill, thats definite. If you look closly you'll see the shear coming of the East side.
"Right said Fred, urh Jeff!"
Small world for sure. I used to cross the bay/bridge tunnel every day to service some equipment over there. Utmost respect for the area and it's people.
On the current track, Bill will miss the strongest shear. This will enable a mostly southerly shearing to continue over the system. That explains its lack of upper-level outflow on the south side. Because he is moving in the direction in which the shear is blowing, he will be slower to weaken.
As ready as one can be for a hurricane. They have VERY strong building codes. Solid concrete is the norm there.
X5tornado's weather input is "XFD owned"?
This means nothing to me. Can you explain?
Thats good, I hope that Bermuda dosn't get hit my any hurricanes... but its eventual I guess.
I sure wish there was a place for hurricanes to landfall so that I could feel better, you all have to admit that when a hurricane reaches Cat. 4, you kind of feel bad when it suddenly weakens and never reaches peak forecasted intensity because of 20 knot wind shear.
So far, this year has been a boon. What with the CreditCrunch badly screwing up the tourism upon which Carribean and Gulf folks depend heavily, the last thing anybody needs is for even more folks to cancel their vacations cuz of hurricane threats.
Unfortunately, we haven't reached the peak of the season yet.
21 GMT 08/20/09 23.8N 63.2W
03 GMT 08/21/09 24.9N 64.3W
11north per 11west ... InvTan(11/11) =45degrees north of West=NorthWest
Closer to ~2.8degrees north of NorthWest after the cosine correction, InvTan(11/11/cos24.9). The distance of one degree on the east-west line shrinks as one travels farther from the equator.)
This first crossing of the NorthWest heading is notable mostly cuz the NationalHurricaneCenter has been fishcasting BigBadBill northwestward since it was a baby blob.
However the central pressure has dropped to a new low, which usually means that the storm is getting stronger. And when a hurricane gets strong enough, it often creates its own environment that overpowers the wind flows and pressure ridges that meteorologists use to forecast future storm positions.
So still gotta keep a watchful eye on the darn thing, and keep our fingers crossed.
Nah, I was saying that you laid the smackdown on him rather well with your question "And your weather input was?", because he was complaining about the socialization on here tonight.
Owned is an internet term that basically means you really told someone off.
Looks like he's right on track to me???? lol
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