There are different ways of measuring the strength of El Niño, the periodic warming of equatorial sea surface temperatures in the Pacific Ocean. Perhaps the simplest, most widely accepted metric is to look at temperatures between 90 degrees west and 160 degrees east longitude, and 5 degrees north and 5 degrees south of the equator, known as the Niño 3.4 region.

The latest analysis from NOAA shows this area of the Pacific had a weekly average temperature 3.0 degrees Celsius above normal, which is a record high. This weekly mark is higher than the 2.8 degrees Celsius anomaly recorded during the week of November 26, 1997, the last really strong El Niño. The NOAA scientists predict El Niño will likely peak during the Northern Hemisphere winter 2015-16, with a transition to neutral conditions during the late spring or early summer 2016.

However it's not clear how much stronger El Niño can get, as there is a finite limit on the amount of warm water available. Additionally, by other metrics, this year's El Niño isn't yet stronger than the previous two biggest events since 1950, during the winters of 1982-1983 and 1997-1998. For example, the average temperature for August through October, this year, was 1.7 degrees Celsius in the Niño 3.4 region, below that of nearly 2.0 degrees Celsius in a comparable period in 1997. In addition, a broader metric that uses both temperature and atmosphere data, the Multivariate ENSO Index, still ranks the 1982-1983 event as the strongest El Niño since at least 1950.

Regardless, this winter's El Niño will cause disruptions around the world, including the United States, especially along the west coast. According to flood insurance data provided by the Federal Emergency Management Agency, since 1978, 37.4 percent of paid claims have come during just four years, 1982, 1983, 1997, and 1998, the years of big El Niños. FEMA advises all homeowners to buy flood insurance.

Floods in California may be exacerbated by the existing exceptional drought in the state. The very dry ground cannot easily absorb rain water, and areas where there are fire scars act like asphalt, allowing water and debris to move quickly downhill. In addition to California flooding, strong El Niño winters are associated with increased tornado activity across the south as well as warmer-than-normal winters across the northern United States.