High Wind — Ern Norton Sound Nulato Hills, Alaska

2022-09-17 · Ern Norton Sound Nulato Hills, Alaska

Event narrative

A measured gust of 52 kt was reported at Shaktoolik AWOS.

Wider weather episode

The remnants of Typhoon Merbok in the northern Pacific Ocean began approaching the Bering Sea on Thursday, September 15, 2022. This storm transitioned into an extra-tropical area of low pressure and strengthened as it traversed the Bering Sea from southwest to northeast. Impacts were first observed with high winds in the Central and Western Aleutians early on Friday, September 16th. The storm continued to move northeast and peaked in intensity on Friday with a minimum central pressure of 937 mb at 4:00 AM, which is the lowest pressure ever recorded in the Bering Sea for the month of September (data since 1950). More remarkably, it appears to have been the lowest pressure recorded for any time of year along portions of its track. The storm slowly weakened but remained very powerful as it moved through the Bering Strait on Saturday morning September 17th, taking a perfect track to bring significant coastal flooding to the northern Bering Sea coast. The storm continued to move northeast into the Chukchi Sea Saturday afternoon, September 17th and stalled out, gradually dissipating through Tuesday, September 20th over the Chukchi Sea.

The impacts on Friday were mainly over the Bering Sea and the Pribilof Islands in the form of high winds and seas. Buoy 46035 in the Bering Sea recorded wind gusts to 76 mph and seas of 52 feet Friday morning. By Friday evening, and into the weekend, the low moved towards the western Alaskan coastline, bringing high winds and near record storm surge.

What made this storm unusual was threefold: Storm strength, storm track, and the speed of its movement. As Merbok's remnants approached the Bering Sea, an eastward transitioning disturbance reinforced the storm's strength by infusing its energy into Merbok's remnants, while merging cold, dry air aloft (pulled from continental east Asia), with the tropical surface air below. This interaction increased the storm's strength exponentially, while facilitating the storm's extra-tropical transition. While it is common to get Hurricane-Force winds during the Fall and Winter in these extra-tropical systems, the strength of the storm was historic for the month of September. Additionally, the Bering Sea's strongest storms typically occur when there is some sea ice present to buffer and protect the coastline from wave action. In September, there is no sea ice in the Bering or Chukchi Seas, leaving the coastline vulnerable to wind driven waves, along with the storm surge.

Also of note were the storm's track and speed of movement. Merbok tracked from the Southwest Bering Sea in a nearly straight line into the Bering Strait at a speed that induced a 'dynamic fetch.' This means that the storm moved at the same speed as the waves it was generating, causing winds to continue to build the same areas of high seas, thus resulting in sea heights over 50 feet. The straight line of the track to the Bering Strait meant that these huge seas, once generated, were sustained by the storm until it deposited these seas into the Western Alaska Coastline. This is what caused the record breaking storm surge at some locations

The first impacts were observed late Thursday afternoon, September 15th, as the storm entered the Bering Sea over the western Aleutians. Wind gusts to 81 mph were reported at Adak early Friday morning. During the later morning hours on Friday, September 16th, a buoy (46035) located west of the Pribilof Islands in the Bering Sea, recorded a series of strong wind gusts. As the storm continued to track northeastward throughout the day, deteriorating weather conditions reached the Pribilof Islands by the afternoon on Friday, September 16th. For the majority of the Western and Central Aleutians, and the Pribilof Islands, the greatest weather impacts were due to damaging winds, and steered marine traffic away from the area.

By early Friday evening, the leading frontal boundary associated with the low arrived over the Yukon and Kuskokwim Delta Coast. Impacts, including damaging wind gusts and storm surge, were observed from the Kuskokwim Delta to the Yukon Delta, as well as farther inland. Storm surge also pushed inland along the Yukon Delta, flooding several communities along the Yukon River. Wind gusts along the coast gusted over 60 mph in several communities with a peak gust of 91 mph reported at Cape Romanzof west of Scammon Bay.

As the storm center reached the Bering Strait on Saturday morning, strong southwest winds pushed a significant storm surge into Norton Sound and the southern Seward Peninsula. Major coastal flooding and severe erosion developed with some communities experiencing the worst flooding in nearly 50 years. Storm surge levels peaked on Saturday, September 17th across the northern Bering Sea but water levels remained at or above flood stage for an additional 12 to 24 hours in some communities.

The storm gradually weakened, slowing its northeasterly movement dramatically as it entered the Chukchi Sea on Saturday September 17th, eventually moving to just west of Point Hope on Sunday September 18th, where it continued to weaken in place through Tuesday September 20th. Due to the weakening of the storm when it moved north of the Bering Strait, impacts were not as severe for communities along the Chukchi Sea coast, with less significant erosion observed and minor flooding. Storm surge levels in the Chukchi Sea peaked on Sunday September 18th.

Source: NOAA Storm Events Database, event_id 1058046. Narrative written by the NWS forecast office that issued the report.