What do you consider bad diving conditions (in terms of wave height, swell, and period)?

[TMHeimer]

I see the big swells on occasion at our house. No wind, no breakers. There are islands on the left and right of our shore, but looking straight out it's open Atlantic. Interesting to see water swells going maybe 10' or more "gently" up the shore and back--like tiny Tsunamis. How gently determines if I dive or not.

 

[redt1de]

I suspect you were looking online at the buoys and that prompted the question about swell height and period. Sites like SurfLine have great data and go a step further. They feed the info in from the offshore buoys into some models to predict how waves will break. Swells are not waves. The big difference is swells are just energy moving through water that do not break. That energy "pools" together over time, usually due to winds or storms offshore and causes those ups and downs. Waves are swells that break due to the height of the swell reaching a certain ratio against the depth of the water it is traveling through. Things on the ocean floor, like ledges, reefs, just approaching the shore or man made things jetties and piers can all cause waves to break. Essentially, as the depth of the water shallows out, the swell becomes unstable, sending the swell crashing forward, thus making a wave. The only time water actually moves is when the wave breaks - throwing it forward - all else, its generally just energy moving through the water. In addition, the shore line can cause waves to break - and are super fun waves to ride (called point breaks, Rincon out here in CA is a famous one).

Wind is another factor. You would think that wind blowing from offshore to onshore (offshore wind), would cause waves to get larger. Not always the case as wind blowing from onshore to offshore (onshore wind), if its going in the right direction, can stand the wave up even higher causing bigger waves. Onshore winds are beautiful for surfing. Constantly changing wind causes conditions that are hard to predict and gives you another variable in which you have to contend.

Agreeing with other posters here that when boat diving you want longer swell periods. But this is precisely the opposite if you are shore diving. Longer swell periods usually means bigger and bigger waves onshore. If you see a 3' swell with a 6 second period, no surfer is super excited. If you see a 3' swell with a 22 second period, suddenly every surfer that can hold a job is calling out sick - waves will be monster. This is of course assuming the swell direction is proper, but if you are shore diving and see a VERY long period with a decent swell size in the right direction, find something else to do unless you can get deep in the water quick and out even faster. If not, you could be staring down overhead breaks and will likely be donating some gear to the deep. It's a dismal science trying to predict how waves will break, but if you surf or shore dive a place long enough, you'll be able to predict whats going on pretty accurately. The easiest way is to make some buddies that know the area and have them take you on as their student.

I'm super lucky as I can both shore dive and surf at places locally. So if its rough - lets surf. If its flat - time to dive.

I see the big swells on occasion at our house. No wind, no breakers. There are islands on the left and right of our shore, but looking straight out it's open Atlantic. Interesting to see water swells going maybe 10' or more "gently" up the shore and back--like tiny Tsunamis. How gently determines if I dive or not.

This is because of swell direction and the bathymetry and structure of the ocean floor. If the swells are not heading the right direction and not working with the bathymetry of the ocean floor, it'll be mushy like you said. Here in SoCal, we are very lucky as we have a lot of different exposures, so if one beach isn't breaking another probably will be. The Wedge might be firing 15 feet waves while a mile down the road at Blackies it is pure glass.

 

[tursiops]

I suspect you were looking online at the buoys and that prompted the question about swell height and period. Sites like SurfLine have great data and go a step further. They feed the info in from the offshore buoys into some models to predict how waves will break. Swells are not waves. The big difference is swells are just energy moving through water that do not break. That energy "pools" together over time, usually due to winds or storms offshore and causes those ups and downs. Waves are swells that break due to the height of the swell reaching a certain ratio against the depth of the water it is traveling through. Things on the ocean floor, like ledges, reefs, just approaching the shore or man made things jetties and piers can all cause waves to break. Essentially, as the depth of the water shallows out, the swell becomes unstable, sending the swell crashing forward, thus making a wave. The only time water actually moves is when the wave breaks - throwing it forward - all else, its generally just energy moving through the water. In addition, the shore line can cause waves to break - and are super fun waves to ride (called point breaks, Rincon out here in CA is a famous one).

Wind is another factor. You would think that wind blowing from offshore to onshore (offshore wind), would cause waves to get larger. Not always the case as wind blowing from onshore to offshore (onshore wind), if its going in the right direction, can stand the wave up even higher causing bigger waves. Onshore winds are beautiful for surfing. Constantly changing wind causes conditions that are hard to predict and gives you another variable in which you have to contend.

Agreeing with other posters here that when boat diving you want longer swell periods. But this is precisely the opposite if you are shore diving. Longer swell periods usually means bigger and bigger waves onshore. If you see a 3' swell with a 6 second period, no surfer is super excited. If you see a 3' swell with a 22 second period, suddenly every surfer that can hold a job is calling out sick - waves will be monster. This is of course assuming the swell direction is proper, but if you are shore diving and see a VERY long period with a decent swell size in the right direction, find something else to do unless you can get deep in the water quick and out even faster. If not, you could be staring down overhead breaks and will likely be donating some gear to the deep. It's a dismal science trying to predict how waves will break, but if you surf or shore dive a place long enough, you'll be able to predict whats going on pretty accurately. The easiest way is to make some buddies that know the area and have them take you on as their student.

I'm super lucky as I can both shore dive and surf at places locally. So if its rough - lets surf. If its flat - time to dive.



This is because of swell direction and the bathymetry and structure of the ocean floor. If the swells are not heading the right direction and not working with the bathymetry of the ocean floor, it'll be mushy like you said. Here in SoCal, we are very lucky as we have a lot of different exposures, so if one beach isn't breaking another probably will be. The Wedge might be firing 15 feet waves while a mile down the road at Blackies it is pure glass.

Much of this post is incorrect, and represents a surfer's poor understanding of waves. Sorry to be so blunt, but when you say things like "Swells are not waves. The big difference is swells are just energy moving through water that do not break" you are way off base.

 

[redt1de]

Much of this post is incorrect, and represents a surfer's poor understanding of waves. Sorry to be so blunt, but when you say things like "Swells are not waves. The big difference is swells are just energy moving through water that do not break" you are way off base.

This was purely a generalization and your credentials seem far superior to mine. I'd be grateful if you'd up my level of understanding. For a lay person like me, this ignorant model works well to decide what break I'm going to head to, or if I want to dive or avoid doing so. But for sure, I'd enjoy to learn the more scientific side of what is actually happening.

 

[tursiops]

This was purely a generalization and your credentials seem far superior to mine. I'd be grateful if you'd up my level of understanding. For a lay person like me, this ignorant model works well to decide what break I'm going to head to, or if I want to dive or avoid doing so. But for sure, I'd enjoy to learn the more scientific side of what is actually happening.

There is a ton of good info online.
The key is that they are all waves: the swell is just an old wave that is no longer being driven by the wind...it is just propagating along through the ocean, slowly dissipating. The waves have a wavelength, the crest-to-crest distance. That wavelength is exactly related to the wave period-- in DEEP water. As the waves approach shallower water, they begin to feel the bottom, and that disrupts the nice relationship between wavelength and period. The longer waves (longer periods, longer wavelengths) feel the bottom first, because their water motion as they propagate along reaches down farther into the water column, so they feel the friction and drag of moving over the bottom. This compresses the wavelength because the rear of the wave is still moving forward, but the front of the wave has slowed down. All that compression causes the wave to grow in height, until it becomes unstable and topples over forwards. That is your breaking wave. Whether an onshore wind wave (shorter period) or an onshore swell (longer period) will break first when it hits a sloping-upwards bottom depends on a combination of the wave height and wavelength.

 

[Bob DBF]

I spent years looking at the NOAA forecasts and buoy data, and then correlating that with what conditions I found at my dive sites (shore diving). Different coves can have different conditions depending on the prevailing wind and wave directions. Spent a lot of days turning around and coming back without diving, still do occasionally.

On boat dives, of which I do not take often, I go unless they cancel. So far I've had no cancellations, but have run into some interesting conditions, actually sat out one dive once.


Bob

 

[TMHeimer]

The DM course teaches you about waves and all their variances, which was very interesting, though not something vital to know. There are no buoys here.

 

[seeker242]

There is a ton of good info online.
The key is that they are all waves: the swell is just an old wave that is no longer being driven by the wind...

Unless it is a wind swell, as that is by definition driven by the wind! As opposed to a ground swell, which isn't.

 

[tursiops]

Unless it is a wind swell, as that is by definition driven by the wind! As opposed to a ground swell, which isn't.

These are surfer terms, not technical terms.

 

[spoolin01]

Surge strength is still mysterious to me - it does not seem clearly related to simple swell height. Some of the worst surge I've seen at the boat ramp has been from fairly low groundswell.

Also, to redt1de - offshore means where the wind is blowing TO, as opposed to easterly, westerly, etc. which of course refer instead to the direction the wind is coming FROM. Keeps everybody happy, and confused.