Make a imageView object containing the launch image, Have that imageView load first in your viewController and then create your webView Object. Once the webView delegate has responded with webViewDidFinishLoad (only called once the website is completely loaded) remove the image object from the view and display the webView.
Personally i would have some sort of activity indicator on screen to show the user there something loading and also implement didFailLoadWithError method in-case the website has problems.