Invariable there will be a few rainy or windy days during your Summer Season. On these days your staff are run off their feet suggesting suitable activities.
Work with your local tourism office to create or update the list of rainy day activities in your destination. The secret is to do more than just create the listing of options. Rather add a paragraph, written in a conversational style, that describes the activity in terms of what it offers, what age groups it is suitable for and the costs.
Make sure that this goes on your website and to your front desk.
Remember that photos make a huge difference to the decision-making of your visitors, so insert a photo for each activity and design your guide as something to look forward to, as opposed to a compromise due to the weather.