BANGKOK, Thailand (AFP) — The arrival of a potentially powerful El Nino weather system this year could devastate coral reefs around the world already weakened by back-to-back rounds of bleaching, scientists warn.

Forecasters are increasingly convinced that this year will see a return of the weather phenomenon, and that it could be exceptionally strong.

El Nino, which occurs around every two to seven years, shifts normal weather patterns on land, bringing drought to some places and heavy rains elsewhere.