I've grown a tomato plant in a Home Depot bucket for about 2 months now. It is an heirloom species called Dwarf Almadine. Recently, the weather has been really damp (mushrooms popping up from the mulch) and hot (can get up to 90 degrees). The tomato leaves have been developing yellow and black spots, especially on older leaves (see picture). 
I have checked all the other posts on this forum and many pictures from the internet. This could either be late blight, rust fungus, or sunburn (less likely). I wonder if anyone has more insights than what I know now.
Anyway, I am going to remove problematic leaves with a pair of scissors. I hope this will stop the spread!
