The rumble started last year and built over the summer into predictions that the Pacific Ocean was gearing up for the pattern we call El Niño. Now, officially, El Niño is here.

Related Content Say Goodbye to a Historic El Niño and Hello to La Niña

The official declaration from NOAA had to wait until the El Niño-like conditions persisted for several months. Over the last month, the indicators finally all pointed to yes. So far the pattern is still borderline, writes Emily Becker for Climate.gov

The last time we had this coupled phenomenon of anomalously warm sea surface and air temperatures off the coast of South America was in 2009-2010. But the last truly strong El Niño was in 1997-1998, when it dumped rain on the West, especially California. What does this El Niño mean for us? Eric Holthaus explains at Slate:

El Niño transfers huge amounts of heat from the oceans to the atmosphere, and there are hints that this El Niño, combined with the already very warm global oceans, could bring about a new phase in global warming. An associated slow-moving indicator of Pacific Ocean temperatures, called the Pacific Decadal Oscillation, reached record levels in December and January. A persistently strong PDO is associated with cold winters in the East and drought in California—we’ve had both in abundance this year. Should the PDO stay strong, it’ll essentially join forces with El Niño and increase the odds that 2015 will rank as the warmest year on record globally.

Another odd thing about this particular iteration of the pattern is its slow onset: Typically El Niño develops in mid-summer, not early spring. The unusual timing may make predictions more difficult, Holthaus says.

Whether or not the pattern stays weak will have to be monitored over the coming months to develop more accurate forecasts. Unfortunately, "[t]his El Niño is likely too late and too weak to provide much relief for drought-stricken California,” says NOAA’s Mike Halpert, in the official statement.