Coral bleaching is not only natural it MUST occur.
Coral outcrops grow upwards towards the sun, like trees, but they can't grow "forever" or they will grow out of the water and die. The vigorous reef grows close to the surface because light is attenuated quickly at depth so the upper limit of the coral is a balancing act of growing close to the surface without drying and dying.
Low tides that occur around noon are lower than those around 6. Check the tide charts. Logically the really low tides, and they vary on a lunar cycle, happening in the heat of the day can expose coral to direct sunlight which can be deadly if there isn't a wind blowing cooling spray over it. Wind droughts are common so bleaching can occur with the confluence of low tides at midday on cloudless, windless days. Island nations exist on "land" that is primarily broken coral so this has been happening for an eternity.
