Normally storms and winds roll through to cool off the surface of the Northern Pacific, but a weather pattern popped up for a few months in winter 2013 that inhibited those storms from developing, said Nate Mantua, a NOAA research scientist. Then, from October 2013 through January, the weather pattern came back as a ridge of high pressure (the same one connected to the California drought). All of that made the already warm waters in the Alaskan gulf even warmer, a layer about 100 meters thick, Mantua said.

In the spring, warm water started to develop in other Northern Pacific waters, namely the Bering Sea. There's also a chunk of warm water developing off the coast of California.