I like having the forum divided. Merging the tropics, or even everything, would make the site look cluttered and disorganized. It is like shoving all your school assignments into one binder lacking even dividers. When you want to find something you have to sift though everything just to find it.
It makes the site feel cleaner to me. Yes, it's not as active here during the hurricane season, but keeping a divide allows for topics to stay in one place. No other forum I know of has a full merger of tropics and standard systems or monthly discussions, so why do it here and make a confusing format for newcomers?
Really I just feel that the forum would be weird having the two major parts of the forum merged. That would mean we would have to merge almost every forum into the main one with the logic of "There isn't enough activity in these parts". The main has the most, the tropics the second, and everything else is the third most active.