Record US temperatures are work of El Niño and polar vortex, experts say

Two weather systems keep 2015 on track to be hottest year ever, with current El Nino phenomenon likely to be one of three strongest in half century

Meteorologists have blamed El Nino and the polar vortex for record-breaking warm temperatures across the US this week, saying the pair of weather systems will likely keep 2015 warm enough to be the hottest year on record.

This year's El Nino, a recurring weather pattern caused by unusually warm water in the Pacific Ocean, is particularly strong and reaching its peak. The high pressure system, now east of Hawaii, sends warm air along the jet stream over the northern Pacific and into the northern and central US.