What are the interior measurements?

What, specifically will be stored here?

Have you considered an outdoor closet, preferably with adjustable shelves, for those things that are actually intended for outdoor use -- beach chairs and other patio style furnishings ?

https://www.google.com/search?q=outdoor+closet&client=firefox-b-1-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwihrqO6pp_wAhXjGVkFHYcsDRAQ_AUoAnoECAEQBA&biw=1366&bih=626

Have you considered a wheeled shelving unit that fits withing your closet but can be rolled out onto the patio or deck or porch?

https://www.globalindustrial.com/p/chrome-wire-shelf-truck-48x24x69-1200-pound-capacity-1

I'd say more baskets -- no towels in piles on floor or shelf, just a basket of beach towels, a basket of toys... Chairs and big things are going to have to lean, but I guess you could put a divider like a middling book end to hold them to one side.

Thank you so much for your creative thinking! My main challenge will be where the wet/sandy towels can go after the beach. I'm trying to avoid the bathroom, and we can't hang them over the railings here. If they shake them out and hang them on hooks or rods in the closet, that may be the best but not ideal solution. I actually like the idea of something rolling that can go in the closet after drying a bit on the rack outside on the deck.

The measurements are: approximately 63" wide and 27" deep. I'd love to pull the brackets off and just add appropriate towel/beach chair/hat hooks.

I will be storing:

Beach towels - clean and post beach/pool use

4 beach chairs

2 boogie boards

1 umbrella

1 beach table (in the green canvas bag)

miscellaneous toys