I haven't spoken much about El Nino in Franklin Facts. That's simply because there hasn't been an El Nino since 1998, and I've been waiting for the topic to become relevant. That time has come: it looks like an El Niņo is developing.

El Nino is a warming of the waters of the central and eastern Pacific Ocean, in the tropics. The warming comes irregularly, usually every three to six years, and its intensity varies from case to case. Over the past year, water temperature observations from a network of buoys deployed across the central and eastern tropical Pacific have showed a slow warming, and computer models suggest the warming trend will continue.

When these Pacific waters warm during an El Nino, they affect the temperature and wind patterns of the atmosphere above as well. There are even indirect connections that can alter the climate in other parts of the globe, including the U.S. Tomorrow night I'll explain how and why this budding El Nino might matter to us.