So apparently a hot wind has less strength than a cold wind. Or is it the other way around?
Isn't 20knots 20 knots everywhere?
I'm awfully confused and would be very thankful is someone explained this to me.

More dense has more power for same speed.
Put you hand up in the air with 40 knot breeze.
Now put your hand in the water going 40 knots.
You find it much harder to put your hand in the water because it is more dense, not because it is going faster!

Now all you gota think it the more dense (heavy) the air is for the same given speed it will have more power to drive your chosen machine

Cold air sinks because it is heavier
Hot air rises because it is light
When the two meet the cold air has more power and wins the battle
So once again the heavier wind has more power.

That's it .The North Sea kiters go out on 3 to 5 m kites.A 7 m is a light wind day! .It would be interesting to see a write up about wind strengths and power ratio between Cape Town and Geralton Wa.Capetown has colder water so its a colder wind , but the heat from WA's midwest land mass just rises so easily that relative colder air from the ocean just sucks in to the low pressure void.

Thanks everyone.

We have done the maths before. 20 Deg C increase in temp is approximately 7% decrease in force

The maths are

Force = 1/2 mass x Velocity squared.

So mass in our instance is the air. Air (or any gas) reduces in density as the temperature rises. At zero Dec C density is approximately 1.29 kg/m3. At 20 Deg C density is 1.2kg/m3.

As you see by the formula Velocity (wind speed) has a far greater effect on force than density. If you increase the wind speed from 19-21 knots the force increases 20%

Now just to confuse you a bit more. More than just temperature affects the density of the air. The pressure does too. The changes in air pressure are minimal at sea level. But you can have a dramatic change at elevation.

Humidity also affects the air pressure. Humid air is less dense than dry air.