Pashuteh Yid – “It would be a terrible shame that frum people could never enjoy the beauty of the sand and ocean, otherwise.”
That may be true, but it is not an adequate reason to do something halachicly questionable. (I am not saying that one should not go to the beach later or earlier than everybody else, only that this last statement has no bearing on the discussion.)
“In addition, those who jog in the summer know that very often it is simply too hot except along the water where there is a constant cool sea-breeze blowing.”
Well than either don’t go jogging or brave the hear, but the halacha is non-negotiable.
“Where I used to live, there was a major street along a river with a jogging path, and the joggers there probably were worse dressed than any beach. What is the halacha in that case?”
I believe there is a Gemora that says that if one has two possible ways to get somwhere, and one he knows he will pass by inappropriately dressed women and one he won’t, he must take the other path even if it takes longer.
“So the question is what must the chances be that something inappropriate will come along in order to make one avoid an activity. 1%, 50%, 100%?”
I would imagine it’s about 50, but then again I’m no posek. So as always, all halacha li’maseh shailos should be asked to your LOR.