I've seen something similar locally -- not with a tree, but with a flowering plant. We're having a drought, and had all of about 2 inches of rain all summer. Then last week, we suddenly got over 4 inches of rain. I'm guessing the flower decided to bloom because it had no chance earlier -- it was too stressed out. It doesn't look like you folks are having a drought, but are you having something else that could have oddly stressed the tree?