It depends on what the occasion is. :) Are you trying to say for a specific event? like "let's meet tomorrow for her birthday party" or is it an unplanned meet up if a certain criteria were met? like "let's meet tomorrow (to go sledding) if it finally snows"? or is it an 'just in case' thing? like "let's meet tomorrow (to buy umbrellas) in case it rains on our trip"?
I hope I didn't make this too difficult or overthink the answer. heh. :D