Pretty common this time of year. Old leaves dropping to be replaced by new ones. Sometimes excessive defoliation can be the consequence of high dissolved solids in the irrigation water, leaving tip burn on the leaves and subsequent drop. Sunburn on exposed limbs can be a result of lack of leaf canopy and limbs can be whitewashed with water-based white latex paint for protection from the sun. By July, all should be fine as the new leaves will appear and your tree should be fine. It is still flowering and that process will continue. I have several trees that do this, but recover by July with no extra care.