Ducted dry air supply into coastal cities?

What you are suggesting is impractical/unlikely for several reasons. How would it work on a technical level? If it were achievable technically then the cost would be astronomical. If you were able to displace such an enormous volume of humid air, then where would it go and what would be the effects? Finally - air conditioning achieves what you want, is readily avaliable, is relatively cheap and can be directed with some precision.