Some people do the MIMS and more than 3 months before high season for channel crossings.
But thinking of Tampa as a “warm-up” might tempt a person to take it less seriously - and that would be a big mistake. TBMS is one of only four annual organized ultra-marathon (25K or longer) swim races in the U.S. (along with Swim Across the Sound), and it may be the toughest. While water temperature is not usually a factor, pretty much everything else is. Glancing through the archives, tide changes and rough seas seem to be the two big ones.
Swimmers typically start with the flood tide, which pushes them up Tampa Bay - for a while. If you don’t swim far enough over the next few hours, though, the tide reverses direction and starts to push you back towards St. Petersburg - making it effectively impossible to finish.
Tampa Bay is also quite large, so conditions can mimic those in the open ocean. Here’s what the Bay looked like in four recent years (click to enlarge photos):
**2010 - 4/7 finished**
**2009 - 7/11 finished**
**2008 - 6/8 finished**
**2005 - 7/19 finished**
Since Ron Collins’ pioneering swim in 1998 (9 hours, 52 minutes), there have been 149 solo entrants in the annual race. Of those 149 swims, 70 were DNF’s - they didn’t finish the full 24 miles. That’s a success rate of 53%. By comparison, over the same time period, 90% of MIMS entrants have successfully rounded Manhattan (239 of 266, not including those who withdrew before the event).
There are other factors at work, of course. The MIMS selection process likely “weeds out” swimmers least likely to finish, based on swim speed or previous cold water marathon experience. I don’t believe Collins has yet rejected anyone from attempting TBMS - which is a good thing, in my opinion.
Tampa Bay has humbled some great swimmers. In one recent edition, a swimmer who is perhaps the best non-professional marathon swimmer in the U.S. retired due to seasickness. Last year, a well known swimming guru (who had twice finished MIMS) planned to swim TBMS, Catalina, and the English Channel, all in the same year. After Tampa (which to his credit, he finished), he decided to withdraw from the latter two swims.
The point is, this swim is a beast. I’m preparing for it as such.