I generally plan my tarpon fishing around both the New Moon and the Full Moon Tides. Generally starting the day before either the new or the full through 3 days after, will give the biggest push of tides to bring the tarpon in to the shallow flats. Of course the weather is an important factor to having good tarpon fishing, probably more so than most other kinds of flats fishing. You would like the water temperatures to be between 75° and 85° plus or minus a few degrees, with little or no wind and of course you'd like to have good visibility (sunshine) in order to see the fish.
I have caught many 100 pound plus tarpon on a fly every month of the year. It is much easier to do that if you live in the area and can pick the proper weather and tide days.
That being said, the last moon tide in March and or the first moon tide in April are 2 of my favorite times of the year to fish for tarpon in the lower Florida Keys. The 2nd moon tide in April, also May and early June would be my choice in the Islamorada area.
For more information on tarpon fishing in the Everglades and Florida Keys, contact Blue Moon Expeditions at 305-849-8254.