The absolute last thing that they want to hear at that time is that the entire problem was not only entirely predictable but, in fact, entirely predicted. Telling them this isn't going to encourage them to listen to you in the future, but it will succeed in ticking them off.
Sadly, these same individuals who you can't say "I told you so" to are also usually incapable of figuring out that they were the ones who put the ship on the reef. Ultimately, this leads to a sort of Captain Queeg syndrome with complaints about co-workers and/or subordinates who are disloyal, the rolling around of steel balls in one's hand, and mutterings about missing strawberries.
(Note that this is somewhat different from the case where a million monkeys have made a million predictions about what might happen. In that case, one of the monkeys is likely to have been correct, but not necessarily because said monkey was particularly good at throwing darts at the wall -- or typing the works of Shakespeare. The monkey is not allowed to say "I told you so" until at least two predictions have come true. :) )
Anyway, for all those out there who need it today, "I told you so".
The rest of you, just carry on about your business.