Can the max water temperature (of a sea or lake) be higher than the average air temperature in the hottest month. (warmest, temperatures)

[markovian process]

Something I'm puzzling over in this thread in the world forum.

//www.city-data.com/forum/33230324-post50.html

It was mentioned that some Canadian waters have 77F/25C temperatures in summer. However, those places do not average 25C even in the warmest month for air temperatures. Their highs are perhaps a little higher than 25C, but the lows are 15-18C, meaning the average is 20C or less.

How can a place have hotter waters than the average air temperature, if the sun is the only source of heat (unless there are extra sources of heat like hot springs or something).

Anyone have a clue?

[Bottletree]

Ocean currents bringing in warmer water?

[markovian process]

Originally Posted by JetsNHL

Ocean currents bringing in warmer water?

Oh, I didn't think of that! Good point.

[Ariete]

Temporarily, yes. We have a small lake at our summer cottage and the water's once in a while warmer than the air temperature after a heat wave. The water temp can be 25C for a few days even if the air temp is 22-23C, as long as it's sunny. Of course, rain, strong winds or unusually cold nights ruins everything, but in small/mid-size lakes with no inflow or currents it's certainly possible. Likely, even, as stagnant water cools down slower than air.

[Joe90]

The sea temperature here in summer, is just about always warmer than the average air temperature. The long term average of the warmest month, has the sea at 1.6C/3.4F warmer than the average air temperature. That's at a deep water location. Shallower spots like beaches etc will sometimes be up to 7 or 8C warmer than the daily average air temperature.

One big reason, is that overnight low temperatures skew the air temperature downwards. The last few nights have seen sea temperatures at between 6-13C lower than the average sea temperature.

In fact, the sea temperature is warmer than the air temperature in every month.

[markovian process]

^^

That's interesting. Does water heat up more easily than it cools down? I'm just figuring out what property of the sea, bay or lake allows for this asymmetry.

[Joe90]

Originally Posted by markovian process

^^

That's interesting. Does water heat up more easily than it cools down? I'm just figuring out what property of the sea, bay or lake allows for this asymmetry.

The air cools down much faster at night, which skews the daily average temperature downwards. The water temperature only changes by about 1-2 C over the day, but the air temperature by 12C in summer.

[markovian process]

Originally Posted by Joe90

The air cools down much faster at night, which skews the daily average temperature downwards. The water temperature only changes by about 1-2 C over the day, but the air temperature by 12C in summer.

But if water is slow to cool down, wouldn't it also be slow to warm up, so how could you build up a hotter temperature in a body of water than the air is on average?

[markovian process]

Oh, I see what you mean. The night cools down faster than the day warms up the air, so over night the water is still warm by the time the sun shines again to add more heat.

I'm guessing this is true during the summer with long days and short nights, so that's why you get really warm waters in summer even in places with not so hot air temps.

[Joe90]

Originally Posted by markovian process

But if water is slow to cool down, wouldn't it also be slow to warm up, so how could you build up a hotter temperature in a body of water than the air is on average?

It's the variation in air temperature that is most relevant, not the variation in water temperature.

The average nightly air minimum is around 8C colder than the sea temperature, while the average daily air maximum is only around 4C warmer than the average sea temperature.