Hello:

People can be pretty understanding and forgiving, if you're honest with them. I would just add a small blurb to your homepage apologizing for the fact that your site isn't completed yet. Offer to contact them when your website is completed. Since your visitors are currently being inconvenienced, by arriving at a website still under construction; tell them you you will give them "priority" notification when your site is completed. Priority sounds better and will make your visitors feel special.