Persian Gulf is the warmest sea June 2, 2014 in Earth Facts / World Facts, Nature Facts The Persian Gulf is the warmest sea. In the summer its temperature reaches 35.6 degrees centigrade. The Persian Gulf is the warmest sea. In the summer its temperature reaches 35.6 degrees centigrade. Review OverviewUser Rating: 4.65 ( 1 votes) 0 facts 2014-06-02 Admin Share ! tweet