Hot, crowded, rainy. Last year was pretty bad. The rain came down in buckets and lasted hours on some days. Alot of flights were cancelled/delayed. When it rained, the lines were short. But it wasn't really that enjoyable. It was nice there were no lines during the big storms, but it didn't make it fun walking around. Another good thing about the rain was that it cooled it down. The weather was really HOT and HUMID. Very uncomfortable. But once the storms moved it, it cooled it down so it was comfortable. The crowds were just crazy busy. We never made it on Soarin. We went on a Monday, which was the recommended day that week, and FP were gone by 10:30am. Of course, this was before FP+. But that shows how busy it was. The line never seemed to slow down.
Alot of people were saying the rain, heat, and crowds were the worst they've seen for the beginning of June. Maybe it won't happen this year. If you have to go in the summer, I would think the first week of June or near the end of August would be your best bet. But personally, I would avoid it.