Summer fog

We have had a prolonged period of beautiful bright sunny weather with almost no wind.  This is very special for Wellingtonians and we tend to flock outside, and especially to the beach, given such a chance - our summers are not always all that warm.  But very little wind can mean odd things happening - on a bright still day a very localised fog suddenly appeared, coming in from the south...

Looking up Island Bay suburb - normally we can see steep hills and houses, but there was just a white blanket. The bay, island, and headland opposite were also completely obscured by dense whiteness - not a very interesting image to post.  This reminded me of another fog exactly three years ago.

That time the fog rolled in on top of the hills.  It was a sunny evening rather than mid-day, but again something from the south was interacting with the warm conditions - it is never particularly humid here, so I am not sure where the moisture was coming from and why it was condensing in this pattern.

It continued in, to cover the hills just like this year's fog.  In the news a person from the meteorological service explained that sea fog is caused when warm air flowing over the cold ocean is cooled, and the moisture (carried in the warm air? or via evaporation from the water caused by the warmth?) condenses.  I can see that the patterns of air movement are important in shaping the fog, but I am puzzled by why it is so localised.  It still seems like another of nature's mysteries for me to learn about!