Re: ? Sail from Lake Erie to Florida late August
You don't mention the kind of boat or your experience level, but be aware that there are three ways you could go.
1. To Chicago and down the Mississippi
2. Through the Erie Canal down the Hudson to New York and south
3. Down the St Lawrence turn right and go south - time in Newfoundland highly recommended.
I have't done #1 and can't comment on schedule or attractiveness of this route. For the other two routes the prevailing wisdom is that going to the Annapolis boat show in early October makes sense. Your insurance coverage may not allow you to be south of a given point (varies, but could be Hatteras or Norfolk) before Nov 1 or with some companies Nov 15,so it works well.
The EC route is much shorter and much easier and quite pleasant. You only need to be in the open ocean from NYC to Cape May which is an easy overnight. The end of August would work fine for this route.
The St Lawrence route is much longer and more challenging and you need to be sel-sufficient, but it gives access to some wonderful cruising grounds. We are 3/4 of the way through a circumnavigation and have not seen anything as spectacular as the south coast of Newfoundland - incredible scenery, whiles, ice bergs, even part of France to visit. Because of distance and weather you would have to leave earlier, perhaps late June.
In either case you would have to keep an eye out for hurricanes from late June onward. Let me know if you have other questions.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.