A powerful extratropical cyclone is expected to blast the western coast of Alaska starting Friday night – bringing potential perils from a storm surge that threatens to top out at 18 feet and gusts that will reach up to 90 mph.
“This is a dangerous storm that will produce widespread coastal flooding south of the Bering Strait with water levels above those not seen in nearly 50 years,” the National Weather Service’s Fairbanks office wrote in its Friday morning forecast discussion. In advance of the dangerous storm, the National Weather Service has issued several warnings to account for a multitude of hurricane-like threats.
As the powerhouse system approaches Alaska late Friday, roaring south-to-southwesterly winds will slam the state’s west coast. Massive amounts of water, shoved north by the high winds, will slosh ashore, raising the ocean as much as a dozen feet and battering vulnerable coastal communities with severe erosion. The storm will probably stall just offshore the Seward Peninsula over the weekend, continuing to push the Pacific toward Alaska’s vulnerable coastline.
“The duration of the high water is quite a bit longer than we often see, so that will lead to a longer duration of high impact surge and waves pounding the coastline,” Ed Plumb, a senior service hydrologist at the National Weather Service’s Fairbanks office, told The Washington Post.
Coastal flood warnings and high wind warnings have been issued, both remaining in effect until late Saturday evening, while storm warnings have been hoisted at sea to warn mariners of extremely dangerous conditions.
Gusts will top out around 90 mph in some spots, with hurricane-force gusts up to 80 mph expected in and around Nome, which is known for being the end point of the famed Iditarod Trail Sled Dog Race.
Water levels in the coastal town of 4,000 are likely to top out at 8 to 11 feet above high tide. In nearby Golovin, water levels will be even higher, pushing 9 to 13 feet above their normal high tide level, according to the Weather Service.
In Nome and other villages along the northern Bering Sea, Plumb worries that water pushed into communities by powerful southwesterly winds will inundate structures, wash out key roads and damage important infrastructure.
Strong gusts of up to 90 mph could also easily take down power lines and cause other damage.
The massive storm surge and gigantic waves that may crest at over 50 feet would cause heavy beach erosion at any time of year, but the fact that the storm is striking in September heightens the erosion risk.
When massive, extratropical storms track through the Bering Sea, it is usually later in the year – particularly into November and December. By that time, sea ice has built up along the coast, buffering significant wave action. But with this major storm striking in September, the coastline is without its icy barrier, making it particularly vulnerable.
“This will be the deepest low we’ve ever seen in the northern Bering Sea in September,” Plumb said, adding that this would be a strong storm at any time of year. “It’s taking the classic textbook perfect track for causing significant storm surge in the northern Bering Sea.”
A September strike is also concerning because it is still hunting season in September, meaning hundreds of people may be hunting in the remote Alaskan wilderness and not getting updates about the storm.
The road that many hunters and Alaskans use to travel inland, the Nome-Council Road, might end up washed away by the storm, leaving off-the-grid hunters stranded in the wilderness.
The system is similar to a disastrous storm from November 2011, when a comparably intense nontropical low pivoted through far eastern Russia, just inland of the Bering Strait.
That month, too, the Pacific was forced inland; in Nome, roads and a sewer plant were swamped, while a number of low-lying coastal communities saw significant erosion wrought by the pounding waves.
“In the Nome area, or that part of the southern Seward Peninsula, everything is on track and it looks like (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 looking at impacts in the United States published in 2018 – scientists expressed concern that climate change has set the stage for greater impacts from large nontropical cyclones in Alaska. Warmer summers and oceans have caused a greater-than-normal seasonal loss of sea ice, which makes the region more vulnerable to ocean inundation.
“For coastal areas, the damage from late-fall or winter storms is likely to be compounded by a lack of sea ice cover, high tides, and rising sea levels, which can increase structural damage to tank farms, homes, and buildings and can threaten loss of life from flooding,” the report reads.
The report adds that coastal erosion rates have been hastening, with some spots on the coastline 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 regions, leading to the loss of terrestrial habitat and cultural resources, and requiring entire communities, such as Kivalina in northwestern Alaska, to relocate to safer terrain.”
The powerful weather system set to blast Alaska is, atmospherically, something of a perfect storm. The remnants of Merbok, once a Category 1-intensity Pacific typhoon, will merge with a pair of nontropical storms as it veers toward the Bering Strait, the thin strip of water between Russia and Alaska.
Typhoons – the Western Pacific equivalent to hurricanes – run on energy from the hot oceanic water common near the equator in late summer. This contrasts with extratropical cyclones, which run on the energy held 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 is forecast to explosively strengthen as it approaches the Alaskan coastline. The system’s pressure is expected to drop 24 millibars in 24 hours, meaning that the storm will have met the criteria for what’s known as a meteorological bomb or “bomb cyclone” due to its rate of intensification.
Such a process strengthened Sandy considerably as it approached the Mid-Atlantic in 2012, and it will dramatically intensify the Pacific storm as it lurches toward Alaska.
By Friday evening, the atmospheric pressure in the center of the storm – set to be over the ocean, a few hundred miles southwest of the Russian/Alaskan border – is modeled to bottom out at around 940 millibars. Low pressure draws air rapidly inward, like a vacuum, and values below 950 millibars are typically seen only in Category 3 or Category 4 hurricanes.
But because the storm, at this point, will be something of a hybrid between a tropical and nontropical low, the wind field will not mimic that of a Category 4 hurricane. Instead, all of that energy will be spread out over a larger area, with a lower maximum sustained wind speed – likely around 90 mph – but with a far greater reach.
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