"In the past month or so, the tropical Pacific has been switching from warm to cold," said Dr Lee-Lueng Fu, a scientist at the US space agency Nasa, where the latest pictures were received.
"The sea level has lowered, and that indicates less heat stored in the ocean - a colder ocean."
This year's El Nino has been the strongest ever recorded, and is blamed for record rain in California and tornadoes in the south-east US, flooding in Peru, drought and fires in Indonesia, and general unsettled - and frequently wet - weather around much of the world.
In Britain, the winter was unusually mild, but Easter brought record floods to many parts of the country.
El Nino - Spanish for "the Boy Child" - is caused when the westward trade winds across the Pacific weaken, and a huge mass of warm water which normally lies off Australia moves east along the Equator until it reaches the coast of South America.
The warm water affects ocean evaporation, allowing more rain clouds to form, and also affects the jet streams which move around the world at high altitude from west to east. But now that it is dissipating, conditions could return to normal - or even flip over to its counterpart, "La Nina", which would mean drier air in the circulating weather systems.
"The effects of El Nino will remain in the climate system for a long time," said Dr Bill Patzert, a research oceanographer at Nasa. "However, if the Pacific is transitioning to a La Nina, we'd expect to see clear, strong indication of it in August or September - just like we did last year with El Nino."Reuse content