LOS ANGELES (AP) — This week’s wet storm isn’t expected to provide much, if any, relief from California’s historic drought. But there is hope for a serious drenching next year in the form of El Nino, a tropical weather pattern over the Pacific Ocean that typically brings rain to the West Coast. Climatologists say the system forming near the equator looks like a big one that has the potential to provide relief from the yearslong dry spell.

Here are some things to know about El Nino:

• WHAT IS IT?

An ocean-warming phenomenon that builds in the Pacific during springtime. Moderate-to-strong events typically bring winter rain and snow to California and the rest of the southwest.

• WASN’T THERE ONE THIS YEAR?

Yes, but it arrived too late to help the drought. There’s a 90 percent chance the current El Nino will last through the summer and a greater than 80 percent chance it will stick around through the end of the year, according to the National Oceanic and Atmospheric Administration. While NOAA says it’s too soon to determine the strength, other scientists say it’s turning out to be quite strong.

• IS NEXT YEAR’S EL NINO A SURE THING?

Definitely not, says climatologist Bill Patzert of NASA’s Jet Propulsion Laboratory. But he says the increasingly warm temperatures in the Pacific along the equator recall conditions back in the spring of 1997, the prelude to a record El Nino year that brought heavy rains to California. “It’s definitely a couple of notches above where we’ve been. Right now it looks like there might be some potential, but there are no guarantees,” he said.

• WHAT’S THE DEAL WITH LA NINA?

El Nino’s flip side, La Nina, is a cooling of the central Pacific. It’s been much more common for the past decade or so. From 2005 to 2014, there have been twice as many months with a La Nina than with El Nino, weather records show.