If your in a good place in the mangroves you shoulnt need an anchor.
Put it in the narrowest channel you can with out having them rubbing the boat. and with with plenty of water under you. the windier the better.
You know which way the storm is comming from so you can predict the direction you want to be pointed. Anchor with the bow facing in the direction
you think the wind will come from in the begining of the storm. and then anchor the stern as well. then run your lines into the magroves. this is what we look for up here but we dont have mangroves we have water oaks and pine trees. When I tie my big boat down. i try not to tie to one tree unless its really massive. where I go there are no big trees so I run the lines out into the woolds and rope up as many trees as I can I have Three 300ft pieces of line expressly for this purpose.
some folks will leave their boat I prefer to be on mine. One its in a better place than my house. Two its self contained power, water so forth.
the problem is the surge right before the storm the water drops, this is why you need a deep channel. then as the storm comes in you start to rise. if you arent there to adjust you could wind up pulling all the cleats off your boat, depending on how high the surge is. During ivan i went down five feet then rose close to ten. thats a pretty big swing if you arent there to adjust
your lines they could get very tight. I don't know if Florida bay suffers from this but I imagine it does. If you find the right size channel your boat would have the anchor straight in front of the boat lines lead forward off both sides of the bow and stern lines lead aft. and a couple of breast lines. and the other anchor straight behind you . remember there will be a lot of current as the water moves in and out with the stom.
If you can only tie one side of your boat to the trees the anchors go at a 45* angles off the bow and stern and if you have extra put them out also.
When you anchor add some extra scope above your normal storm range to account for surge. When the water starts to rise you will want to slack off the tree lines. let the anchors come tight, slack the tree lines this will keep you out of the woolds. at one point during Ivan I had no tention on my bow line slacked off on my stern anchor to get the wind on the other side of the bow. when It came over the bow line went tight an we hauled in on the anchor to keep us pointed in to the wind. It had more east in than I thought it would. We were side tied to the trees and had anchors on one side.
The whole trick is getting the boat pointed into the wind at the begining when its the worst. so the lee side of a key or hammock get your bow lines runnig to the mangroves and put your anchor spread off the stern three anchors would be the least I would want in this case. But for me I like being surrounded. If the leading edge hits you in the face the trailing edge will kick you in the butt.
hope this helps