Strongest storm in decades expected to hit Alaska with coastal flooding and high winds

A powerful extratropical cyclone is expected to blast the west coast of Alaska from Friday evening – bringing potential dangers of a storm surge that threatens to peak at 18ft and gusts that will reach up to 90mph.

“This is a dangerous storm that will produce widespread coastal flooding south of the Bering Strait with water levels above those seen for nearly 50 years,” the Fairbanks office of the National Weather Service wrote in his statement. Friday morning forecast discussion. Ahead of the dangerous storm, the National Weather Service issued several warnings to account for a host of hurricane-like threats.

Threats of high winds and coastal flooding

As the power plant system approaches Alaska on Friday evening, roaring south to southwest winds will slam the state’s west coast. Massive amounts of water, pushed north by high winds, will lap on the shore, lifting the ocean up to a dozen feet and hitting vulnerable coastal communities with severe erosion. The storm will likely stall just off the Seward Peninsula over the weekend, continuing to push the Pacific toward the vulnerable Alaskan coast.

“The duration of high water is a bit longer than what we often see, which will lead to a longer duration of high-impact surge and shore-beating waves,” said Ed Plumb, principal duty hydrologist at the office of Fairbanks from the National Weather Service. , told the Washington Post.

Coastal flooding and high wind warnings were issued, both remaining in effect until late Saturday evening, while storm warnings were issued at sea to warn sailors of extremely dangerous conditions.

Gusts will reach around 90mph in some places, with hurricane-force gusts of up to 80mph expected in and around Nome, which is known to be the end point of the famous Iditarod Trail sled dog race.

Water levels in the coastal town of 4,000 are expected to reach 8 to 11 feet above high tide. In the nearby town of Golovin, water levels will be even higher, pushing 9 to 13 feet above their normal high tide level, according to the Meteorological Service.

In Nome and other villages in the northern Bering Sea, Plumb worries that water driven into communities by strong southwesterly winds will flood structures, wash away major roads and damage important infrastructure.

Strong gusts of up to 90 mph could also easily bring down power lines and cause other damage.

The massive storm surge and gigantic waves that can peak over 50 feet would cause severe beach erosion at any time of the year, but the fact that the storm hits in September increases the risk of erosion.

The Perils of a September Storm

When massive extratropical storms cross the Bering Sea, it’s usually later in the year, particularly in November and December. At that time, sea ice built up along the coast, dampening the heavy wave action. But with this major storm hitting in September, the coastline is deprived of its ice barrier, which makes it particularly vulnerable.

“It will be the deepest depression we have ever seen in the northern Bering Sea in September,” said Plumb, adding that it would be a strong storm at any time of the year. “He’s taking the perfect classic route to bring a major storm surge to the northern Bering Sea.”

A strike in September is also concerning because it is still hunting season in September, which means hundreds of people can hunt in the remote wilderness of Alaska and not receive storm updates.

The road that many hunters and Alaskans use to travel inland, the Nome-Council Road, could end up being washed away by the storm, leaving off-grid hunters stranded in the wild.

The system is similar to a disastrous storm in November 2011, when a non-tropical depression of comparable intensity rotated across far eastern Russia, just inside the Bering Strait. Also that month, the Pacific was forced inland; in Nome, roads and a sewage treatment plant were flooded, while a number of low-lying coastal communities experienced significant erosion from pounding waves.

“In the Nome area, or that part of the southern Seward Peninsula, everything is on track and it seems [this storm] will be as bad or worse than the 2011 superstorm,” Plumb said.

In the Fourth National Climate Assessment, a comprehensive climate change report examining impacts in the United States published in 2018 – scientists have expressed concern that climate change has paved the way for greater impacts from large non-tropical cyclones in Alaska. Warmer summers and oceans have caused greater than normal seasonal sea ice loss, making the region more vulnerable to ocean flooding.

“For coastal areas, damage from late fall or winter storms is likely to be compounded by a lack of sea ice cover, high tides and sea level rise, which which can increase structural damage to tank farms, homes and buildings and can threaten loss of life from flooding,” the report read.

The report adds that rates of coastal erosion have accelerated, with some shoreline locations losing up to 100 feet of land to the sea each year.

“Longer sea ice-free seasons, higher ground temperatures and relative sea level rise are expected to worsen flooding and accelerate erosion in many areas, leading to loss of terrestrial habitats and cultural resources. , and requiring entire communities, such as Kivalina in the northwest. Alaska, to move to safer ground.

A weather-perfect storm

The powerful weather system put in place to blast Alaska is, atmospherically speaking, something of a perfect storm. The remnants of Merbok, once an Intensity Category 1 Pacific typhoon, will merge with a pair of non-tropical storms as it turns toward the Bering Strait, the thin strip of water between Russia and Alaska.

Typhoons – the equivalent of hurricanes in the Western Pacific – run on the energy of warm ocean waters common near the equator in late summer. This contrasts with extratropical cyclones, which operate on the energy contained in atmospheric temperature gradients.

When the two types of systems merge, the combination can result in an extremely powerful storm that forms in a short time. This system is expected to strengthen explosively as it approaches the Alaskan coast. The system’s pressure is expected to drop by 24 millibars in 24 hours, meaning the storm will have met the criteria for what’s called a weather bomb or “cyclone bomb” due to its rate of intensification.

No need to bend down and take cover – it’s the “bomb cyclone”, explained

Such a process has significantly strengthened Sandy as it approaches the mid-Atlantic in 2012, and it will greatly intensify the Pacific storm as it heads into Alaska.

On Friday evening, atmospheric pressure at the center of the storm – which is expected to be over the ocean, a few hundred miles southwest of the Russian-Alaskan border – is modeled to reach around 940 millibars. The low pressure sucks air in quickly, like a vacuum, and values ​​below 950 millibars are usually only seen in Category 3 or 4 hurricanes.

But because the storm, at this point, will be something of a hybrid between a tropical and non-tropical depression, the wind field won’t mimic that of a Category 4 hurricane. Instead, all that energy will be spread over a larger area, with a lower maximum sustained wind speed – likely around 90 mph – but with a much greater range.

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