Unusual and unusually intense cyclone hits Alaska

A powerful oceanic cyclone unprecedented in intensity at this time of year caused a lot of havoc on the west coast of alaska, bringing massive flooding to coastal communities and wind gusts of 150 km/h. The National Weather Service in Fairbanks, which issued warnings for both coastal flooding and wind, said the storm was “producing tidal surges unprecedented in at least 50 years.”

As coastal communities in western Alaska dealt with floodwaters that inundated homes and businesses, Governor Mike Dunleavy declared a state of disaster. Large amounts of water, pushed northward by strong winds, rushed over land, lifting the ocean several meters and hitting vulnerable coastal communities with severe erosion.

The tide gauge at Nome, which is known to be the endpoint of the famous Iditarod Trail Sled Dog Race, showed water levels more than three above normal levels early Saturday, exceeding the peak seen during the fierce storms of 2011 and 2004, according to the National Weather Service.

Social media reports indicated power outages and damage to several coastal communities from rising waters. In Hooper Bay, a small coastal town of 1,375 people, some families reportedly left their homes because of the flooding. Major flooding was also reported in the small coastal communities of Chevak, Kotlik, Newtok, Golovin and Shaktoolik, where evacuations were necessary in several cases.

Strong 150 km/h gusts knocked down power lines and caused other damage. The massive storm and tidal waves of up to 15 meters would generate heavy erosion on the beach at any time of year, but the fact that the storm hits in September increases the risk of erosion.

When large extratropical storms make their way through the Bering Sea, it is usually towards the end of the year, particularly in November and December, and Cyclones can be powerful many times in Alaska. It turns out that at this time of year, sea ice has built up along the coast, dampening significant wave action, but with this big storm in September, the coastline is without its ice barrier, making it particularly vulnerable.

The system is similar to a disastrous storm in November 2011, when a comparatively intense non-tropical low hit Russia’s Far East and Bering Strait interior. In that month, too, the Pacific advanced over land.

In the Fourth National Climate Assessment, a comprehensive report on climate change looking at impacts across the United States published in 2018, scientists expressed concern that climate change has set the stage for greater impacts from large, non-tropical cyclones in Alaska. Warmer summers and oceans have caused a greater-than-normal seasonal loss of sea ice, making the region more vulnerable to oceanic flooding.

The powerful weather system that hit Alaska is a “perfect storm”, defined the meteorologists of the Washington Post newspaper. The remnants of Merbok, once a Category 1 Pacific typhoon, joined non-tropical storms as they headed into the Bering Strait, the thin strip of water between Russia and Alaska, forming an extraordinary extratropical cyclone, a bomb cyclone.

Typhoons, the equivalent of hurricanes in the Western Pacific, form from warm ocean water common near the equator in late summer. This is in contrast to extratropical cyclones, which run on energy contained in atmospheric temperature gradients.

When the two types of systems merge, the combination can result in an immensely powerful storm that forms in a short time. This system explosively strengthened upon entering the Bering Sea. The same process considerably strengthened the Sandy approaching the Northeast coast of the United States in 2012.

On Friday, atmospheric pressure at the center of the storm reached about 937 millibars over the Bering Sea, the lowest in the region in September since 2005. Low pressure draws air quickly in, like a vacuum, and below 950 millibars are typically only seen in Category 3 or Category 4 hurricanes.

But because the storm at this point is something of a hybrid between a tropical and non-tropical low, the wind field was much larger than it would be in a Category 4 hurricane. Instead, all the energy was spread over a larger area, with a lower maximum sustained wind speed, probably around 150 km/h, but with a much greater range.

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