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Author Topic:   Wave Height Variation

logjam posted 10-25-2010 05:14 PM ET (US)
I have followed with interest several threads running at the same time in which whaler drivers are kind enough to share their experiences with their whalers performance in heavy weather.
I bring this up as a reminder of how variable waves can be within a geographic area.
In the book Oceanography and Seamanship, William G. Van Dorn provided an example of what the wave heights would be if a steady 33 mph (30 knots) wind blew for 24 hours over a fetch of 340 miles.
10% of all waves will be less than 3.6 ft (1 m).
The most frequent wave height will be 8½ ft (2½ m).
The average wave height will be 11 ft (3 m).
The significant wave height will be 17 ft (5 m).
10% of all waves will be higher than 18 ft (5 m).
The average wave height of the highest 10% of all waves will be 22 ft (7 m).
A 5% chance of encountering a single wave higher than 35 ft (11 m) among every 200 waves that pass in about 30 minutes.
A 5% chance of encountering a single wave higher than 40 ft (12 m) among every 2,600 waves that pass in about five hours.

This does not include a host of other variables including swell from different directions, currents, current opposing wind or swell, depth, storm surge, interference, internal waves, diffraction, refraction, reflection, or a dozen other things I'm probably forgetting.
I'll always remember jumping in an 18' guardian on a flat calm sunny day for a run to another location. I didn't even throw on my rubber boots but chose leather for the comfort of hiking around when I got there. Along the way I encountered some kind of opposing currents along with a localized breeze that did it's darnedest to try and fill me up. It didn't matter how fast or slow I tried to go every wave went in the boat by several inches. I was trying to perch on the leaning post and drive at the same time. It only lasted for less than a mile and I had to laugh but I wouldn't have been laughing in a kayak or even a 13' whaler.
I realize that the lack of a photo, video, or supporting NOAA documentation means that it didn't happen so I would encourage someone to provide photo shop help to give my post credibility.

WT posted 10-25-2010 07:55 PM ET (US)
When I talk about wave height I usually assume the same definitions as NOAA.
WVHT according to NOAA means "Significant wave height (meters) is calculated as the average of the highest one-third of all of the wave heights during the 20-minute sampling period."
So in this case the WVHT in Bodega Bay as of 3:50 PM PDT is 16.4 feet (converted to feet from meters).
http://www.ndbc.noaa.gov/station_page.php?station=46013
Here are the other definitions.
http://www.ndbc.noaa.gov/measdes.shtml
Yes, there are variations to wave information.
Warren
anthonylisske posted 10-25-2010 07:58 PM ET (US)
Logjam,
Good info. They should give that type of info out with every boat sale. I am going to look up the reference and do some "post mortum" of my bad recent day.
I was suprised at the difference between average and "significant" wave hieghts. I did not realize the significance of "significant", lol
I have more to read and learn. Thanks
WT posted 10-25-2010 08:21 PM ET (US)
Wow! Bodega Bay is at 18.7 feet at 4:50 pm PDT.
If this keep up, it doesn't look like I'll be going out this weekend either.....
Bummed out,
Warren
WT posted 10-25-2010 08:43 PM ET (US)
Lots of us estimate the size of waves/swells like we estimate the size of our fish. I like to check the NOAA reading during my time on the water to get a real reading of the conditions while I was on the water.
Here is a thread when we (the Strike 3 gang, Tony, Matt and I) went out on the salmon opener this year. We were out when swells hit 17 feet during our outing. 17 feet sounds big but when the intervals are long, it isn't that big a deal.
Anyway, NOAA readings just give you a better idea of the water conditions.
Warren
K Albus posted 10-25-2010 08:46 PM ET (US)
They're expecting 27-footers on Lake Superior, tomorrow.
OPEN LAKE FORECAST FOR LAKE SUPERIOR
NATIONAL WEATHER SERVICE MARQUETTE MI
423 PM EDT MON OCT 25 2010
FOR WATERS BEYOND FIVE NAUTICAL MILES OF SHORE ON LAKE SUPERIOR
* * *
LAKE SUPERIOR FROM SAXON HARBOR WI TO UPPER ENTRANCE TO PORTAGE CANAL MI 5NM OFF SHORE TO THE US/CANADIAN BORDER INCLUDING ISLE ROYALE NATIONAL PARK - LAKE SUPERIOR FROM UPPER ENTRANCE TO PORTAGE CANAL TO MANITOU ISLAND MI 5NM OFF SHORE TO THE US/CANADIAN BORDER- 423 PM EDT MON OCT 25 2010
GALE WARNING IN EFFECT FROM LATE TONIGHT THROUGH TUESDAY
MORNING
STORM WARNING IN EFFECT FROM TUESDAY MORNING THROUGH LATE
WEDNESDAY NIGHT
* * *
TUESDAY
EAST GALES TO 40 KNOTS BECOMING SOUTH STORM FORCE
WINDS TO 50 KNOTS BY EARLY AFTERNOON. AREAS OF FOG THROUGH EARLY AFTERNOON. A SLIGHT CHANCE OF THUNDERSTORMS THROUGH EARLY AFTERNOON. RAIN SHOWERS. WAVES BUILDING TO 20 TO 25 FEET.

TUESDAY NIGHT
SOUTH STORM FORCE WINDS TO 55 KNOTS VEERING SOUTHWEST AFTER MIDNIGHT. A SLIGHT CHANCE OF THUNDERSTORMS THROUGH MIDNIGHT. RAIN SHOWERS LIKELY. WAVES BUILDING TO 22 TO 27
FEET.
WT posted 10-25-2010 08:46 PM ET (US)
http://continuouswave.com/ubb/Forum1/HTML/019329.html
logjam posted 10-26-2010 01:08 AM ET (US)
I agree that the NOAA WX buoys are a good source of information, and I always check the forcasts and actual conditions before going, but just because two wx buoys show similar information doesn't mean that you won't encounter waves twice the size they are reporting.
There are so many variables and so far we have just talked about wave height. As some of the variables affect the waves in different ways their form changes, their speed changes, their direction changes. The only thing you can count on is that you haven't seen it all yet.
jimh posted 10-26-2010 09:16 AM ET (US)
Van Dorn's model for wave height is for wind waves and for deep water. If there is an opposing current or if there are shoreline effects, such as shoaling, wave height will be affected.
The Canadian continuous marine forecast broadcast always says, "Wave height forecasts are for offshore and are measured from trough to crest. Wind and waves can vary considerably due to shoreline effects."
elaelap posted 10-26-2010 11:05 AM ET (US)
Yep, shoreline effects. Out here we fish for groundfish and sometimes salmon in very shallow water (15-40 ft), often so close to rocks that we can literally reach out and touch them with our rods. Our Pacific seas almost always provide at least five or six foot swells, which on a calm day aren't even noticeable offshore a ways. But woe betide the careless fisherman who heads way inshore carelessly watching only the backs of the building waves, even when they're small. As those modest swells reach shoreline depths approximating three times their height, their intervals become shorter and they begin to dramatically rear up and hollow out, and heaven help the Whaler caught inside of them when that happens.
We lost several experienced fishermen earlier this year in exactly that fashion, fishing too close to our deceptively mellow-appearing "Ten Mile Beach." Last year a couple of very experienced local boaters ate it on the Tomales Bay bar, and several years back another local guy -- "Napa Stan" -- almost died along with his fishing buddy when they got sideways to an inshore break in Stan's Outrage 18 (the boat was a total loss; the fishermen survived thanks to their Mustang floatation jackets, which encouraged me to buy and always wear one while boating in these conditions).
Each of us who boats and fishes out here has several tales of close calls and near misses when fooling around close to shore, when something caused us to look seaward just in time to spin our boats into a hollow or breaking swell and give it full power, be damned to trailing fishing lines and other gear. Shoreline effects -- brrrrr...
Tony
K Albus posted 10-26-2010 11:15 AM ET (US)
Locally, some of the wave forecasts for the Great Lakes and the wave forecast for Lake St. Clair have recently started to include forecasts for "Significant Wave Height" and "Maximum Wave Height", which the forecasts define as follows: "SIGNIFICANT WAVE HEIGHT IS THE AVERAGE OF THE HIGHEST 1/3 OF THE WAVE SPECTRUM. MAXIMUM WAVE HEIGHT IS THE HIGHEST 1/20 WAVE HEIGHT."
For instance, the forecast for today for Lake St. Clair reads as follows:
THIS AFTERNOON
SOUTHEAST WINDS TO 30 KNOTS WITH GUSTS TO 50 KNOT STORMS. WIDESPREAD SHOWERS WITH NUMEROUS THUNDERSTORMS...SOME STORMS
MAY BE SEVERE. SIGNIFICANT WAVES 3 TO 4 FEET. MAXIMUM WAVE HEIGHT AROUND 7 FEET.
In the recent past, this forecast would have stated something to the effect of "Waves 3 to 4 feet" without any warning of the potential for larger waves.
logjam posted 10-26-2010 12:06 PM ET (US)
All of the NOAA WX buoys in my area are in deep water so don't reflect the shoreline effects and effects of a strong ebb with opposing swell in the bars. Still I find them very useful while at sea to keep from being surprised while fishing in those most dangerous areas as an early warning system of sorts. I check them periodically, if I'm fishing a dangerous place or if I see something on the horizon or detect a wind shift, or if the forecast is marginal. Sometimes they allow me to push a marginal forecast a little longer. If winds, seas,or swell start arriving 50 or 100 miles from my location I vacate the most dangerous areas and cross bars before they close.
The national weather service gives station reports on marine VHF WX channels. To use them you must know where your weather buoys are and what their numbers are.
Sometimes the NOAA Dial a Buoy number(888-701-8992)gives more updated and detailed information and I have those numbers in the cell phones I carry aboard. If you don't use it often enough to remember the station numbers you can list them in your cell phones as well.
I also have ATIS and AWOS telephone numbers in my cell phone to check current WX conditions at several airports at key locations and use them for their advanced warning. They don't have sea state but all the other weather information is there and they are usually more accurate and reliable than the buoys, with up to the minute information.

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Author	Topic: Wave Height Variation
logjam	posted 10-25-2010 05:14 PM ET (US) I have followed with interest several threads running at the same time in which whaler drivers are kind enough to share their experiences with their whalers performance in heavy weather. I bring this up as a reminder of how variable waves can be within a geographic area. In the book Oceanography and Seamanship, William G. Van Dorn provided an example of what the wave heights would be if a steady 33 mph (30 knots) wind blew for 24 hours over a fetch of 340 miles. 10% of all waves will be less than 3.6 ft (1 m). The most frequent wave height will be 8½ ft (2½ m). The average wave height will be 11 ft (3 m). The significant wave height will be 17 ft (5 m). 10% of all waves will be higher than 18 ft (5 m). The average wave height of the highest 10% of all waves will be 22 ft (7 m). A 5% chance of encountering a single wave higher than 35 ft (11 m) among every 200 waves that pass in about 30 minutes. A 5% chance of encountering a single wave higher than 40 ft (12 m) among every 2,600 waves that pass in about five hours. This does not include a host of other variables including swell from different directions, currents, current opposing wind or swell, depth, storm surge, interference, internal waves, diffraction, refraction, reflection, or a dozen other things I'm probably forgetting. I'll always remember jumping in an 18' guardian on a flat calm sunny day for a run to another location. I didn't even throw on my rubber boots but chose leather for the comfort of hiking around when I got there. Along the way I encountered some kind of opposing currents along with a localized breeze that did it's darnedest to try and fill me up. It didn't matter how fast or slow I tried to go every wave went in the boat by several inches. I was trying to perch on the leaning post and drive at the same time. It only lasted for less than a mile and I had to laugh but I wouldn't have been laughing in a kayak or even a 13' whaler. I realize that the lack of a photo, video, or supporting NOAA documentation means that it didn't happen so I would encourage someone to provide photo shop help to give my post credibility.
WT	posted 10-25-2010 07:55 PM ET (US) When I talk about wave height I usually assume the same definitions as NOAA. WVHT according to NOAA means "Significant wave height (meters) is calculated as the average of the highest one-third of all of the wave heights during the 20-minute sampling period." So in this case the WVHT in Bodega Bay as of 3:50 PM PDT is 16.4 feet (converted to feet from meters). http://www.ndbc.noaa.gov/station_page.php?station=46013 Here are the other definitions. http://www.ndbc.noaa.gov/measdes.shtml Yes, there are variations to wave information. Warren
anthonylisske	posted 10-25-2010 07:58 PM ET (US) Logjam, Good info. They should give that type of info out with every boat sale. I am going to look up the reference and do some "post mortum" of my bad recent day. I was suprised at the difference between average and "significant" wave hieghts. I did not realize the significance of "significant", lol I have more to read and learn. Thanks
WT	posted 10-25-2010 08:21 PM ET (US) Wow! Bodega Bay is at 18.7 feet at 4:50 pm PDT. If this keep up, it doesn't look like I'll be going out this weekend either..... Bummed out, Warren
WT	posted 10-25-2010 08:43 PM ET (US) Lots of us estimate the size of waves/swells like we estimate the size of our fish. I like to check the NOAA reading during my time on the water to get a real reading of the conditions while I was on the water. Here is a thread when we (the Strike 3 gang, Tony, Matt and I) went out on the salmon opener this year. We were out when swells hit 17 feet during our outing. 17 feet sounds big but when the intervals are long, it isn't that big a deal. Anyway, NOAA readings just give you a better idea of the water conditions. Warren
K Albus	posted 10-25-2010 08:46 PM ET (US) They're expecting 27-footers on Lake Superior, tomorrow. OPEN LAKE FORECAST FOR LAKE SUPERIOR NATIONAL WEATHER SERVICE MARQUETTE MI 423 PM EDT MON OCT 25 2010 FOR WATERS BEYOND FIVE NAUTICAL MILES OF SHORE ON LAKE SUPERIOR * * * LAKE SUPERIOR FROM SAXON HARBOR WI TO UPPER ENTRANCE TO PORTAGE CANAL MI 5NM OFF SHORE TO THE US/CANADIAN BORDER INCLUDING ISLE ROYALE NATIONAL PARK - LAKE SUPERIOR FROM UPPER ENTRANCE TO PORTAGE CANAL TO MANITOU ISLAND MI 5NM OFF SHORE TO THE US/CANADIAN BORDER- 423 PM EDT MON OCT 25 2010 GALE WARNING IN EFFECT FROM LATE TONIGHT THROUGH TUESDAY MORNING STORM WARNING IN EFFECT FROM TUESDAY MORNING THROUGH LATE WEDNESDAY NIGHT * * * TUESDAY EAST GALES TO 40 KNOTS BECOMING SOUTH STORM FORCE WINDS TO 50 KNOTS BY EARLY AFTERNOON. AREAS OF FOG THROUGH EARLY AFTERNOON. A SLIGHT CHANCE OF THUNDERSTORMS THROUGH EARLY AFTERNOON. RAIN SHOWERS. WAVES BUILDING TO 20 TO 25 FEET. TUESDAY NIGHT SOUTH STORM FORCE WINDS TO 55 KNOTS VEERING SOUTHWEST AFTER MIDNIGHT. A SLIGHT CHANCE OF THUNDERSTORMS THROUGH MIDNIGHT. RAIN SHOWERS LIKELY. WAVES BUILDING TO 22 TO 27 FEET.
WT	posted 10-25-2010 08:46 PM ET (US) http://continuouswave.com/ubb/Forum1/HTML/019329.html
logjam	posted 10-26-2010 01:08 AM ET (US) I agree that the NOAA WX buoys are a good source of information, and I always check the forcasts and actual conditions before going, but just because two wx buoys show similar information doesn't mean that you won't encounter waves twice the size they are reporting. There are so many variables and so far we have just talked about wave height. As some of the variables affect the waves in different ways their form changes, their speed changes, their direction changes. The only thing you can count on is that you haven't seen it all yet.
jimh	posted 10-26-2010 09:16 AM ET (US) Van Dorn's model for wave height is for wind waves and for deep water. If there is an opposing current or if there are shoreline effects, such as shoaling, wave height will be affected. The Canadian continuous marine forecast broadcast always says, "Wave height forecasts are for offshore and are measured from trough to crest. Wind and waves can vary considerably due to shoreline effects."
elaelap	posted 10-26-2010 11:05 AM ET (US) Yep, shoreline effects. Out here we fish for groundfish and sometimes salmon in very shallow water (15-40 ft), often so close to rocks that we can literally reach out and touch them with our rods. Our Pacific seas almost always provide at least five or six foot swells, which on a calm day aren't even noticeable offshore a ways. But woe betide the careless fisherman who heads way inshore carelessly watching only the backs of the building waves, even when they're small. As those modest swells reach shoreline depths approximating three times their height, their intervals become shorter and they begin to dramatically rear up and hollow out, and heaven help the Whaler caught inside of them when that happens. We lost several experienced fishermen earlier this year in exactly that fashion, fishing too close to our deceptively mellow-appearing "Ten Mile Beach." Last year a couple of very experienced local boaters ate it on the Tomales Bay bar, and several years back another local guy -- "Napa Stan" -- almost died along with his fishing buddy when they got sideways to an inshore break in Stan's Outrage 18 (the boat was a total loss; the fishermen survived thanks to their Mustang floatation jackets, which encouraged me to buy and always wear one while boating in these conditions). Each of us who boats and fishes out here has several tales of close calls and near misses when fooling around close to shore, when something caused us to look seaward just in time to spin our boats into a hollow or breaking swell and give it full power, be damned to trailing fishing lines and other gear. Shoreline effects -- brrrrr... Tony
K Albus	posted 10-26-2010 11:15 AM ET (US) Locally, some of the wave forecasts for the Great Lakes and the wave forecast for Lake St. Clair have recently started to include forecasts for "Significant Wave Height" and "Maximum Wave Height", which the forecasts define as follows: "SIGNIFICANT WAVE HEIGHT IS THE AVERAGE OF THE HIGHEST 1/3 OF THE WAVE SPECTRUM. MAXIMUM WAVE HEIGHT IS THE HIGHEST 1/20 WAVE HEIGHT." For instance, the forecast for today for Lake St. Clair reads as follows: THIS AFTERNOON SOUTHEAST WINDS TO 30 KNOTS WITH GUSTS TO 50 KNOT STORMS. WIDESPREAD SHOWERS WITH NUMEROUS THUNDERSTORMS...SOME STORMS MAY BE SEVERE. SIGNIFICANT WAVES 3 TO 4 FEET. MAXIMUM WAVE HEIGHT AROUND 7 FEET. In the recent past, this forecast would have stated something to the effect of "Waves 3 to 4 feet" without any warning of the potential for larger waves.
logjam	posted 10-26-2010 12:06 PM ET (US) All of the NOAA WX buoys in my area are in deep water so don't reflect the shoreline effects and effects of a strong ebb with opposing swell in the bars. Still I find them very useful while at sea to keep from being surprised while fishing in those most dangerous areas as an early warning system of sorts. I check them periodically, if I'm fishing a dangerous place or if I see something on the horizon or detect a wind shift, or if the forecast is marginal. Sometimes they allow me to push a marginal forecast a little longer. If winds, seas,or swell start arriving 50 or 100 miles from my location I vacate the most dangerous areas and cross bars before they close. The national weather service gives station reports on marine VHF WX channels. To use them you must know where your weather buoys are and what their numbers are. Sometimes the NOAA Dial a Buoy number(888-701-8992)gives more updated and detailed information and I have those numbers in the cell phones I carry aboard. If you don't use it often enough to remember the station numbers you can list them in your cell phones as well. I also have ATIS and AWOS telephone numbers in my cell phone to check current WX conditions at several airports at key locations and use them for their advanced warning. They don't have sea state but all the other weather information is there and they are usually more accurate and reliable than the buoys, with up to the minute information.