04 JAN 2021
On New Year’s Eve, the far western reaches of the Aleutian Islands were rocked by the most powerful storm ever recorded in the North Pacific – the equivalent of a Category 1 hurricane if it had occurred in the tropics.
Two days in advance, the National Weather Service issued a warning for all waters between Atka to Adak for waves of 40-50 feet, hurricane-force winds and gusts up to 85 miles per hour. As the storm passed over, an ocean buoy at Amchitka Island recorded significant wave heights exceeding 58 feet.
The New Years Eve storm passed directly over Shemya, the remote home of Eareckson Air Station, some 700 nautical miles to the west of Dutch Harbor. The runway complex is best known for its very large missile defense radar array, AN/FPS-108 Cobra Dane – a 1970s-era ballistic missile tracking system operated by Raytheon for the U.S. Space Force. The base’s weather station recorded a low pressure of 924.8 millibars, setting a new record low for sea level pressure in the state of Alaska. The previous record was set in Unalaska in 1977, when a ship recorded a low of 925 millibars.
The storm occurred with a boost from the polar jet stream, the high altitude winds that transit the North Pacific in the mid-latitudes. The jet stream was forecast to hit 200 knots at the time the storm arrived in the Aleutians. “Unlike hurricanes, [maritime cyclones] derive their energy from an entirely different process. While hurricanes extract heat from the ocean, maritime cyclones create energy by drawing together warm and cold air masses. When the warm air rises and cold air sinks, the kinetic energy of swirling wind is generated,” said Capital Weather Gang’s Jeff Halverson in a 2015 discussion. “The juxtaposition of warm and cold air is also what powers the polar jet stream – and indeed, maritime cyclones and the jet stream are inextricably linked – the one feeding back upon, and enhancing, the other.”