Others may have suggestions but my dad used to let the garden hose drip, drip, drip all day and all night for about two weeks when a new tree was planted. Just a tiny bit of a drip. Adding some mulch around the base of the tree will help to conserve moisture especially with high temperatures.
Don't know if there is much wind where you are but new trees also need some protection from wind; both sun and wind will dehydrate a newly-planted tree.
