A positive PDO just means there is more warmth in the tropical Pacific region, plus in the other areas in the North Pacific that go along with a positive PDO, such as near certain portions of the North American coast. The backdrop of more warm water in the tropical Pacific means a lowered tendency toward La Nina. Some scientists believe that the PDO is no more than a cumulative effect of recent ENSO activity (e.g., in the current case, the big El Nino), while others think that the PDO also does its own thing, independent of ENSO.