At the end of July when you plan to travel, you will run into dream week. Hotels will be booked out solid, increased tourist activity in the day, but the beach road will be a roadblock at night.
You may enjoy this and you can pay daily to get into the events if that's your scene.

Weather will be hot and dry, there is always a bit of rain in negril, no matter when you go. Not a lot in July and August . The sea will be beautiful and warm at this time.