The weather phenomenon known as La Niña, caused by a cooling of the Pacific Ocean’s surface, is officially here, the National Weather Service announced Thursday on Twitter. Meteorologists say La Niña is poised to cause extreme weather worldwide, including worsening fire conditions in the American West amid what is already California’s worst fire year on record and even more devastating fires from Washington to Arizona. “We’re already in a bad position, and La Niña puts us in a situation where fire-weather conditions persist into November and possibly even December,” Ryan Truchelut, president of Weather Tiger LLC, told Bloomberg. The weather pattern might also contribute to more severe hurricanes in the Atlantic and flooding in Australia and South America. It increases the probability of a colder winter in the northern U.S.