Diving Utilization Edition


Absolutely recommended for diving! Free weather forecast app ” Windy” Predict wind speed, waves, seawater temperature, temperature, weather, ocean currents, and tides

Introducing safety measures against waves and swells during diving.

 Diving  Entry & Exit

When entering or exiting a place with waves and swells, it is basic to aim for the timing when the waves are small.

The surf zone is especially strong, so try to get out of it as quickly as possible.
Also, in the case of boat diving, when entering and exiting, leave the boat immediately so as not to hit the boat with the swell.
Before entering, check the weather information for the day with the weather layer items of, swell, swell 2, swell 3, wind wave, and try to dive safely! !

beach diving entry & Board diving entry


What are waves?

Waves are a combination of waves generated directly by the wind (wind waves) and gently rounded waves (swells) caused by wind waves generated in distant places.
There are two types of waves: wind waves and swells. Waves are affected by topography.

①wind waves: Waves caused by the wind

②Swells:Waves :propagated by wind-generated waves in other sea areas are called swells.
Typical examples of swell include waves caused by the aftermath of storms.
Swells have a longer period and longer wavelength than wind waves.



What are waves, swells, swells 2, swells 3, wind waves at

The definitions of waves, swells, swells 2, swells 3, and wind waves in the weather layer items of are as follows.

Waves: Significant wave height and its period of all wave types combined (swell and wind waves). Close to the shoreline, the actual height is influenced by the shape of the sea bottom.

Swell1: A swell consists of wind-generated mechanical waves that are not significantly affected by the local wind at that time. They have been generated elsewhere and some time ago, usually travelling long distances.

Swell2: Secondary swell is produced also by winds far away but in other places than Swell1. It has different heights, directions and periods than Swell1.

Swell3: Another secondary swell, with different heights, directions and periods than Swell1 and Swell2. More detailed info about the swells is here.

Wind waves: Wind waves, or wind-generated waves, are surface waves that occur on the free surface of bodies of water (like oceans, seas, lakes, etc.). They result from the wind blowing over an area of water surface. Wind waves are generated by the immediate local wind – which gives them the direction. After the wind ceases to blow, wind waves are called swells.

引用先:Description of weather overlays Examples of waves, swells, swells 2, swells 3, wind waves Examples of waves, swells, swells 2, swells 3, wind waves Examples of waves, swells, swells 2, swells 3, wind waves

Basically, all you have to do is look at the “waves” on the layer.
Check the size and direction of the waves while being conscious of what size and angle they are entering the diving  point.

We believe that the influence of swells will change depending on the environment such as the location of the surf point, direction, and topography.

Therefore, “swell 2” may be helpful at one point, and “swell 1” may be helpful at another point.


Diving and wave height guidelin

The guideline for safe diving entry is from solid calm to 1.2m.It is dangerous at the level where whitecaps are standing more than 1.5m.Also, if the wind direction is offshore, it is dangerous even if it is over 1m.

meters(m) feet(ft) Body  part   heigh Surfing    skill
0.3048 0ft beginner
0.6096 1ft Shin Beginner intermediate
0.9144 2ft knee to thigh intermediate
1.2192 3ft waist to belly intermediate
1.524 4ft chest to shoulder Advanced


Diving and Wave Cycle Guide

The interval between sea waves in normal times is about 3 seconds.
With this numerical value, it is not a swell but a wind wave, and the wave period is wind wave up to 6 seconds.
If the wave period is 6 seconds or more, the wave is suitable for surfing. As the wave period increases, the speed of the wave increases, so the power also increases.
If the swell exceeds 10 seconds, it is a dangerous swell for diving.

Wave period Note
6 seconds or less, jumbled waves It is a newly born weak swell that is not suitable for Diving.Areas with forecasts in this range have rough seas and strong onshore winds.
7-9 seconds wind waves, uneven waves Wind wave range. The maximum swell that can be dived is up to 7 seconds.
10- seconds    Big waves A swell generated in a place some distance away due to strong winds.There is energy that can reach far away.

The swell is unsuitable for diving, so stop diving and exit immediately.

Diving and Significant Wave Height

Wave heights used in weather forecasts are usually expressed as significant wave heights.

Significant wave height is the average value of the top 1/3 of all wave heights arranged in descending order, which is close to the wave height that people intuitively perceive.
However, even with this convenient “significant wave height”, larger and smaller waves are generated. For example, 1 wave in 10 waves is 1.3 times the significant wave height, 1 wave in 100 waves is 1.6 times the significant wave height, and 1 wave in 1000 waves is twice the significant wave height.
In addition, one wave in thousands or tens of thousands of waves may be several times the significant wave height, and this is called a big wave.

In this way, waves with high heights that occur stochastically, even though they are small in proportion to the whole, are called big waves.

times.Therefore, when entering the beach, look offshore and make sure there are no high waves.

Surfing and Significant Wave Height


Diving and Shallow Water Effect

The shallow sea effect is “a phenomenon in which wave height, wave speed, and wavelength change due to the influence of the seabed when waves enter shallow sea areas (shallow sea areas), causing refraction and wave breaking.“

When a wave from offshore enters a shallow water area, if the water depth becomes shallower than 1/2 of the wavelength, the wave height, wave speed, and wavelength will change due to the influence of the seabed.

In sea areas where the water depth is 1/2 to 1/6 of the wavelength, the shallower the wave height, the lower the wave height, which is about 90% of the original wave height.

However, when the water depth becomes shallower than that, the trend reverses and the wave height rises rapidly.

Also, the wave speed tends to decrease as the water depth becomes shallower, and the wavelength tends to become shorter.

“Swell” has a longer wavelength and period than “Wind wave”, so it has the property that the wave tends to rise due to the shallow sea effect.

Therefore, swells coming from offshore can suddenly become high waves near the coast, and accidents involving waves can occur, so caution is required.



Diving- Onshore, Offshore

If you plan to go beach Diving, check the wind direction on to make sure the wind direction is offshore and suitable for Diving .

Offshore (wind that blows from the shore toward the sea)
conditions are good and the waves are good.

For diving, strong offshore winds can prevent you from returning to shore.



Onshore (wind that blows from the sea toward the shore) conditions It becomes a turbulent, jumbled wave.

In the case of diving, strong onshore winds may prevent you from going offshore.



Diving    Check seawater temperature

Estimated sea surface temperature at the actual time. For locations close to the coastline, the actual values are affected by the coastline, seabed shape, wind and waves.
Before surfing, use to check the water temperature and choose the best wetsuit.

As the depth increases, the water temperature usually decreases.
However, near the surface of the sea, there is a layer with little change in water temperature in the depth direction, a surface mixed layer.

In the case of Japan, the seawater near the sea surface is warmed by solar radiation in the summer, and the temperature difference between the sea surface and the lower layer becomes large, so the surface mixed layer becomes thinner.

In winter, seawater is cooled on the surface of the sea, and wind blowing over the sea actively stirs the water in the upper and lower layers, forming a thick surface mixed layer.

Surfing- Check seawater temperature



Surfing Sea water temperature and wet suit

Seawater temperatures and suitable wetsuits for comfortable Diving are as follows.

Diving-Find back wind!

In diving, if there is a strong offshore wind (wind blowing from the shore toward the sea), you will not be able to return to the original shore, so do not enter.
Therefore, when looking for a place with weak wind even a little, use Windy to search for the back of the wind.

For example, the point in the left image below has a wind speed of 5 m/s, but if you click the white point ○ on the opposite side of the island and move it, you can find a weak wind point with a wind speed of 3 m/s.



water surface movement

Waves and swells may push back divers moving on the water surface.
In such a case, instead of trying to force yourself to move forward, you can proceed smoothly by riding the waves that move in the same direction as the direction of travel.

Since the tidal currents have a large effect on the coast, use Windy in advance to check the tidal currents and then move smoothly on the water surface.



The weather forecast app is a free app that tells you the weather conditions at a glance on a screen that visualizes weather information around the world.

However, it is prohibited to be overconfident with alone.
Please also check the weather forecast of  others App.


Windy  Related article

Windy’s related article is below, please refer to it.

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