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Alaska can expect more big storms like September’s ex-typhoon, as ocean continues to warm

A screenshot of an aerial view of the incoming September storm that hit Western Alaska. Storm Track from Rick Thoman with UAF ACCAP.
A screenshot of an aerial view of the incoming September storm that hit Western Alaska. Storm Track from Rick Thoman with UAF ACCAP.

The storm that slammed into western Alaska over the weekend was the result of several factors all converging to make it so destructive.

That’s according to Rick Thoman, a climate scientist at the University of Alaska Fairbanks, who says Tropical Storm Merbok initially formed farther to the east of Japan than one would expect and picked up energy from water that was much warmer than it used to be, based on historical records.

Then, as the upgraded Typhoon Merbok became an “ex-typhoon,” low pressure aloft picked it up and pushed it north into the Bering Sea. And, Thoman says, the orientation of the Jet Stream — a high-altitude band of strong wind — was such that the storm’s edge tracked right along hundreds of miles of Alaska’s coastline, causing severe damage.

Thoman says, as ocean temperatures continue to creep upward, similar, huge, devastating storms hitting Alaska could become more likely.


Interview with Rick Thoman

The following transcript has been lightly edited for clarity.

Rick Thoman: Without the very warm ocean water, you just don’t get these tropical cyclones. Now, as it moves north over cooler water, it transitions to the “ex” portion of Merbok, or like a typical mid-latitude storm structure. That might sound like just a meteorological technicality. But in fact, it’s incredibly important, because typhoons, hurricanes, are actually fairly small features as far as storms go. They’re compact. And when they transition to the mid-latitude structure, they expand greatly. They grow in size. And that was a key portion of the impact. The center is passing west of St. Matthew Island, and we’re getting this tremendous flooding hundreds of miles east, on the Alaska coast.

Casey Grove: Tell me more about that. What did we see as far as the wind speeds and the water levels?

RT: Wind speeds in most places, Well, to the extent we know, were not super high. The highest gusts, for instance in Nome, 59 miles an hour at the airport. In some places we don’t actually know what the highest gusts were, because power went out at the airport. But, certainly, many places had winds of 55 to 65 miles an hour. Some exposed places had wind gusts up above 80 miles an hour. But more than the peak wind speeds, it was really the duration of very high winds, of gale-force winds, 30 to 50 miles an hour sustained winds, for 18 to 30 hours, depending where you’re at. And that’s really what drove the water up, those strong sustained winds, pushing the water, acting as a plow, if you will, just moving that water. And where that moved into south- or west-facing coastlines, that water just piles in there and is pushes it up. So it was really the duration of the winds in most places, rather than the absolute highest gusts.

CG: Gotcha. Yeah, that’s interesting. So there were major impacts, obviously. We haven’t heard about any deaths at this point. But certainly people lost their homes, and there was quite a bit of advance warning. Really, I mean, you could see this coming from a long ways away. There were computer models. But does it seem like there was much of a response, I guess, before the storm?

RT: Yes, this was very, very well forecast by the large scale models. Was every detail correct? Of course not. But certainly the models were showing the threat of a major Bering Sea storm. By Monday afternoon, it was clear that something big was going to happen somewhere in the western Alaska coast. And by Tuesday, the models had converged on a track that was very close to what actually happened. But to the extent that that information got out there, a lot of information on social media, there’s always ways to improve the communications. But I think the important thing that we need to keep in mind is in rural Alaska, we need to provide as much lead time as we can. We need to give people the heads up. And I think, you know, this is a stormy part of the world. Storms happen in western Alaska. They’re gonna happen again. And when something is really out of the ordinary, we need to make sure as many people know about that as long in advance and know this was not just another storm.

CG: Yeah, speaking of another storm, I guess, just in the sort of short-term future, there was some speculation that there was another typhoon forming that may come towards us. What is that storm called? And is that actually going to hit Alaska, do you think?

RT: Super Typhoon Nanmadol, affecting southern Japan. At this point, though, that does look like that is going to dissipate long before it gets to Alaska. There is a slight chance that it could move along the Aleutians as a very weak storm, but definitely nothing like what we just saw.

CG: Well, then, looking forward further into the future, you know, years into the future, can we expect these kinds of storms to happen more as the climate continues to warm?

RT: Well, to get a storm like this, as we talked about, you have to have all the pieces fall in place. And of course, most of the time they don’t. However, I think this is a really important wakeup call for Alaska, in the sense that Merbok formed in an area that we just simply don’t ever expect tropical systems to form. It’s, historically, the water is not warm enough. But the water is warm enough this year, and we are certain that in the coming years, coming decades, the oceans will continue to warm. And so, although Merbok formed in an area where it’s extremely rare, it’s very likely going forward, over years, decades, we will see more storms in that part of the Pacific, and that is much closer to Alaska than storms curving east of Japan.

Casey Grove, Alaska Public Media - Anchorage