Swell, waves, and period

[Maj92az]

I have been boating on lakes. I took my great weather for granted.
I recently learned about swell and swell period. The only example of swell I recall is (while on a 10x2 mile lake) is not necessarily the choppy water above- but the water as a whole rising and rolling- happened rarely on the lake I was on.

My question is.. for the ocean.. a bay. Or inland Long Island Sound.. I am reading the swell at 2ft (for example) and a period of 4 seconds. But what about the actual waves....I picture this swell a rolling rising body of water but what about the forecast that indicates the actual local waves....

The forecast does include wind speed. I see often 10 knots. Or am I thinking too much about it and the swell...is the waves...

 

[Lou C]

take a look at this website, it is from the Univ of Conn, they have weather and wave buoys across LI Sound and it gives you the wave height and period. For a given wave height the shorter the period is the more choppy it will be, 4 sec is pretty short, so that will be a rough day if in smaller boat. LI Sound can get nasty when it gets windy and there can also be large wakes from oil tankers and barges around Northport where the power plant is located.
As far as winds, anthing over 15 mph is not going to be comfortable in a smaller boat, due to the waves created. The other thing you don't have in lakes is tides. If the tide and wind are moving in opposite directions, that is when the biggest waves are created and makes inlets very dangerous.

UConn's Long Island Sound Observatory

CLIS Waves | Long Island Sound Integrated Coastal Observing System

sampling interval is 60 minutes ©1999-2022 University of Connecticut

mysound.uconn.edu

WLIS Waves | Long Island Sound Integrated Coastal Observing System

sampling interval is every 30 minutes ©1999-2022, University of Connecticut

mysound.uconn.edu

during storms these meters can peak at approx 10 feet but during Superstorm Sandy they were off the chart
Often the conditions in local harbors will be calmer than what's happening in LI Sound, this is why you should have a hard mount VHF radio and check the weather before heading out. I look at both, the UConn site and the marine weather.

 

[Scott Danforth]

oceans go from flat calm (sea state 0) to 15 foot peaks (sea state 7) very quickly

Beaufort Scale

since you are moving. talk to the locals

 

[Maj92az]

Thanks. I will be taking my journey seriously and I will be asking locals and taking my time. Heck I might not be out on my own until 2023.

I suppose my question was .. when I read a forecast and it says swell "1-2ft" or 5ft. Are those actual waves reaching that high or is that just a rolling swell. When I picture a wave- I picture a wave crashing at the shoreline. Please excuse me for my quite elementary question. I currently am staring at a cactus and the only water around is from my garden hose.

 

[Scott Danforth]

Waves are swells, until they get to shore and the dip collides with the shore

 

[dingbat]

Not sure about LIS but around here the accuracy of the marine wave forecast is a running joke.

Swell is wind-generated waves that have traveled out of their generating area. Typically fall out from offshore hurricane or tropical storms as they pass thru the area.

The one to watch is significant wave heights or “Seas” as it is commonly called. The average height (trough to crest) of the one-third highest waves.

Here is the kicker….heights equivalent to the average of the highest one-third of all waves observed. Individual waves may be more than twice the significant wave height.

Here is the forecast for my area for the next couple of days.,

Baltimore Canyon to Cape Charles Light to 100 NM offshore
434 PM EDT Wed Sep 15 2021

TONIGHT...S winds 10 to 20 kt, diminishing to 5 to 15 kt. Seas 3 to 4 ft. Chance of showers and tstms.

THU...SE winds 5 to 15 kt, becoming E 10 to 20 kt. Seas 3 to 5 ft, building to 6 to 10 ft. Scattered showers and tstms.

THU NIGHT...E to NE winds 15 to 25 kt. Seas 7 to 13 ft. Scattered showers and tstms.

FRI...N to NE winds 20 to 30 kt. Seas 6 to 11 ft. Scattered showers and tstms.

FRI NIGHT...N to NE winds 15 to 20 kt. Seas 6 to 10 ft.

Now go back and read the “kicker” . Yes…30’ waves are possible during this event…(continental cold front passing through the area)

Note how the direction of the wind has a bigger affect on wave height than the actual wind speeds.
Local knowledge is key

 

[Maj92az]

It has crossed my mind on how accurate the forecasts can be. I suppose it should be taken very lightly and after much experience some connection can be made once someone is knowable to a local area.

I am curious where the 30' came from. Is that a definition of advertising a avg wave height? one-third? I read 10ft (and a 13ft).

 

[dingbat]

It has crossed my mind on how accurate the forecasts can be. I suppose it should be taken very lightly and after much experience some connection can be made once someone is knowable to a local area.

Most like myself have gave up on the forecast. No where close..... to many localized weather anomalies.
Took it upon myself many years ago to take an interest and learn weather to forecast for myself. Lots and lots of weather data out there once you understand how the pieces fit together.

I am curious where the 30' came from. Is that a definition of advertising a avg wave height? one-third? I read 10ft (and a 13ft).

A "wave" isn't a single entity.

This will help to understand the complexities of a wave spectrum and how "SWH" is calculated.

Mariners Weather Log Vol. 50, No. 1, April 2006

The 30' comes from the warning on the forecast page....."Individual waves may be more than twice the significant wave height.

Case in point.........SWH is the average height of the tallest waves in the spectrum....5', 10' and 30' = Average 15...tallest was 30

 

[TheOceanCoach]

If you're confused, you're in good company. It's a bit complex. Let's set aside the terms "seas" and "waves" for now and concentrate on swell.

Swell does not exist unless the wind blows for several days over hundreds of miles. Both are required to make swell. Lakes don't have swell because they're not big enough. Same with bays. Swell only exists on the open ocean.

Once swell is created, it travels until it hits a beach somewhere and breaks. Swell routinely travels thousands of miles. For example, some of the largest swells that hit Southern California originate in New Zealand.

Swell is characterized by height and period, where period is the time between passing crests.

The terms "seas" and "waves" usually refer to a combination of swell and wind chop.

An excellent book on the subject is Waves and Beaches, by Willard Bascom and Kim McCoy.

 

[QBhoy]

Hi. Having spent 10 years working and living on the sea in my early days…occasionally boating on the family big boat in the sea (Wild West coast of Scotland) and from day one to the present day sustained, on the fresh water loch I’ve boat on and was brought up on too….I can perhaps tell you my thoughts on it all..

Firstly I’d say that it really depends on the particular area involved. Between sea and lake.
A big swell of worrying reported or forecast heights, can often be something that wouldn’t bother a boat or the skipper. Can be often big gentle and widespread apart ordeal. Where as often on a lake like the one I mainly boat on…you can have a horrendous and dangerous short, sharp and violent wave or chop. Very uncomfortable at best.
But then again…here on the west coast, in the sea, you can see varying and unpredictable wild weather out of nowhere.
Either way, something that deserves a little respect, as you’ll know. But all I’d say is that a swell can be sometimes an almost unnoticeable thing…it’s more often a shorter frequency and breaking chop (often caused by shallow water or surrounding hill or land formation) that can be dangerous.

 

[racerone]

On the lake in my area you can have 6' to 8 ' waves during a windy day.----Then if the wind dies down the waves keep rolling along and it takes the swell a few hours to die down.

 

[QBhoy]

On the lake in my area you can have 6' to 8 ' waves during a windy day.----Then if the wind dies down the waves keep rolling along and it takes the swell a few hours to die down.

Just shows you about the various different conditions, spending on the locality.

 

[KJM]

I have been boating on lakes. I took my great weather for granted.
I recently learned about swell and swell period. The only example of swell I recall is (while on a 10x2 mile lake) is not necessarily the choppy water above- but the water as a whole rising and rolling- happened rarely on the lake I was on.

My question is.. for the ocean.. a bay. Or inland Long Island Sound.. I am reading the swell at 2ft (for example) and a period of 4 seconds. But what about the actual waves....I picture this swell a rolling rising body of water but what about the forecast that indicates the actual local waves....

The forecast does include wind speed. I see often 10 knots. Or am I thinking too much about it and the swell...is the waves...

How big is the boat you will be using? The size of the boat makes a big difference as to what wave height is safe. As a rule I find swell is like you said, slow rolling up and down and not too much to worry about on its own if you watch your speed. You can have a big swell on a perfectly calm day as the swell is from storms in other parts of the ocean. Local wind generated waves are more the worry.

 

[KJM]

If you're confused, you're in good company. It's a bit complex. Let's set aside the terms "seas" and "waves" for now and concentrate on swell.

Swell does not exist unless the wind blows for several days over hundreds of miles. Both are required to make swell. Lakes don't have swell because they're not big enough. Same with bays. Swell only exists on the open ocean.

Once swell is created, it travels until it hits a beach somewhere and breaks. Swell routinely travels thousands of miles. For example, some of the largest swells that hit Southern California originate in New Zealand.

Swell is characterized by height and period, where period is the time between passing crests.

The terms "seas" and "waves" usually refer to a combination of swell and wind chop.

An excellent book on the subject is Waves and Beaches, by Willard Bascom and Kim McCoy.

Swell can and do exist in bays depending on the local topography and swell direction. If they are coming straight in from the mouth of the bay. Can even be amplified somewhat as the bay narrows in and gets shallower.

 

[Grub54891]

I don't mind swells as long as they are farther apart, to close together and you get kicked hard! And the swells can contain wave also.

 

[dingbat]

On the lake in my area you can have 6' to 8 ' waves during a windy day.----Then if the wind dies down the waves keep rolling along and it takes the swell a few hours to die down.

By definition, the phenomenon of swell can not be truly realized even in the largest lakes.

I believe the phenomenon of which you speak is called Seiche

 

[racerone]

I have seen a Seiche more than once.-----The lake where I am located is fairly big.-----I can not see the shore on the other side.

 

[racerone]

Surface of the lake is 23,000 square miles/

 

[dingbat]

Surface of the lake is 23,000 square miles/

Huron?
Wife’s family has lived within eye sight of the lake for five generations. Fished out of Port Sanilac and Lexington many times over the years.

 

[racerone]

Huron , it is.----Been at Port Sanilac during yacht racing stop over.