We have been to Ocho Rios many times in July and the weather has been great. Never humid on this side of the island because of the way the wind keeps the air moving. It is a lot less humid in Ocho Rios than in Florida in July. In Negril, the wind does not do this and the area in general is more humid do to the wet nature of the area.
The Hurricane season does start in June, but storms and fronts are normally not until September and October. Not a big worry about storm other than the half hour a day on the Ocho Rios side. Negril side we have never been to in July, so someone else needs to answer.
You will have no problem on the Ocho Rios side and I am sure that the Negril side is also fine based on the amount of people that go during July.
We've been to Negril twice in July and once in January. It is definitely hotter in the summer and more humid. We don't mind either...we actually like it so it doesn't bother us. And if it ever gets too hot, we simply jump in the ocean or the pool. No problem.
We love August weather. Yes it is humid and hot, but we love it. We do spend the days floating in the ocean or the pool which is wonderful, with a cool drink. Does not get any better. Planning on being at CN this coming August.