Catastrophe Q&A: Researcher
7 min read

Catastrophe Q&A: Researcher

The hurricane researcher discusses this year’s forecast and the debate about extending the season.
Catastrophe Q&A: Researcher

Colorado State University’s Phil Klotzbach, Part 1

With the official start of the 2021 Atlantic Hurricane season a little over a month away insurers and reinsurers will soon see if they have prepared their balance sheets to withstand the onslaught. A key forecast for the insurance industry comes from Phil Klotzbach, research scientist in the Department of Atmospheric Science at Colorado State University.

In the first part of this interview, Risk Market News speaks with Dr. Klotzbach about this year’s Atlantic basin hurricane forecast and the controversial debate about extending the hurricane season.

Risk Market News: First, could you summarize this year’s Hurricane forecast and some of the contributing factors that shaped it?

Phil Klotzbach: The seasonal hurricane forecast we just put out from Colorado State is calling for another above average Atlantic hurricane season in 2021 with a total of 17 named storms.

Of those 17, eight will become hurricanes.

And of those eight, four will become major category 3, 4 or 5 hurricanes on the Saffir-Simpson Hurricane Wind Scale. That means those are hurricanes with winds of 111 miles per hour or greater.

That compares with the last 30 year average of about 14 named storms, seven hurricanes and three major hurricane. Somewhat of an above normal forecast for 2021.

RMN: Is there anything that you saw in this year's forecast that is particularly fueling this number of storms?

Klotzbach:There were a few of big factors that we look at.

One of the big factors we look at every year is whether or not we're going to have an El Nino event. An El Nino is warmer than normal waters in the eastern and central tropical Pacific Ocean. When you get warmer than normal waters in the Eastern and Central tropical Pacific Ocean, that is what tends to increase upper-level winds in the Caribbean that extends out into the tropical Atlantic. Those stronger upper-level winds, say between 20,000 to 30,000 feet in the atmosphere, tear apart hurricanes. Unfortunately for this hurricane season, we don't anticipate an El Nino event in the tropical Pacific. We've got to anticipate the winds at higher levels in the atmosphere could be more conducive for hurricanes.

The other big factor that we're monitoring is that the waters — not necessarily in the tropical Atlantic but a little farther north in the subtropical Atlantic — are somewhat warmer than normal. And when those waters are warmer than normal during the early spring, that tends cause wind patterns that are weaker over the tropical Atlantic. So you get weaker winds blowing across the tropical Atlantic that causes less mixing and less churning up of the ocean surface. So the tropical Atlantic then warms, and a warmer tropical Atlantic provides more fuel for the hurricanes since a hurricanes fuel source is that warm ocean water.

RMN: Over the longer term, what are your thoughts on the frequency and severity of tropical storms and are there any longer-term trends that surprise you?

Klotzbach: We’ve been in a generally active period for Atlantic hurricanes since about 1995. We've had some quiet seasons in there as well, a lot of those quieter seasons were driven when we had the stronger El Nino events. But in general since 1995 Atlantic hurricane seasons have been more active.

Overall, if the Atlantic basin is more active than you tend to get more storms making landfall in the Caribbean, as well as hitting the United States.

But if you go back prior to that from 1970 to 1994, the Atlantic tended to be quite a bit quieter, only about half as much major hurricane activity as in recent years. If you go back before that from the mid '40s to the late 1960s, Atlantic hurricane seasons in general were more active. So we've been in this active era since 1995. At some point we do anticipate to switch to a quieter period where Atlantic hurricane activity will become less frequent, but at least at this point, at least for 2021, we anticipate this active period to continue.

Overall we do see this kind of this multidecadal variability in Atlantic hurricanes. If you look back at, say since 1950 or so, we don't see any pronounced trends overall in Atlantic basin wide activity. Perhaps the storms are getting a little bit stronger. The storms may also be a little more volatile and may be intensifying at more rapid rates. This is the so-called “rapid intensification” events where storms intensify 40, 50 miles an hour in a day. And obviously those can be huge problems, especially when they do like they did last year where we had a lot of these storms rapidly intensifying up to about the point of landfall.

RMN: Do you think once there is a shift over to a less frequent number of storms that the number of storms experiencing rapid intensification will also decrease?

Klotzbach: Probably somewhat because, in general, the rapid intensification happens with stronger storms as you would expect. Obviously, if storms are rapidly intensifying they're likely to also hit higher thresholds, higher overall intensity. So that number may drop at least in the Atlantic.

But if you look globally at storms activity, so you have hurricanes in the Atlantic, but you also get hurricanes in the eastern Pacific Ocean, you get typhoons in the western Pacific Ocean, you get cyclones in the southern hemisphere. If you look globally at storm activity, the last say 20, 30 years have actually been generally fairly quiet globally. So the Atlantic's been active but the Pacific has been much, much quieter. And there's actually been a downward trend in that. But if you look at overall, even with that downward trend, rapidly intensifying events do seem to be going up.

So even if the Atlantic goes into a quieter period and the Atlantic cools relative to the rest of the tropics, the overall warming of the global oceans is likely to probably cause more of these rapid intensification events in the future as well.

RMN: What are your thoughts on extending the hurricane season?

Klotzbach: There's a lot of discussion right now.

There hasn't been much talk about extending the end of the hurricane season. We haven't had a lot of storms forming in December. Even last year with our 30 storms, still the season shut down by the middle of November.

But there is talk of extending the hurricane season earlier, so moving it back from June 1 to May 15. They're not doing it for 2021 but there was some discussion about it. And we have seen, at least in the last few years, some early season storms prior to the official start of the hurricane season. we get storms, say in the latter part of May.

Now these storms and later May have generally been fairly weak and they haven't been particularly impactful. Nut we do occasionally get storms early in the season since those typically formed in the western Atlantic where the waters are warmer. Those storms tend to form close to land so they can still have some impacts.

And we have seen storms the first week in June, early June most notably probably tropical storm Alison back in 2001, that was a very weak storm overall, but obviously brought tremendous rainfall to the Houston metropolitan area. It formed the first week in June but what's to say couldn't form the last week in May.

There's some questions about extending the hurricane season to encompass some of these weaker short-lived storms in late May. So from one perspective you could say “yes”, but the other challenge is that the Atlantic hurricane season is extremely peaked. You get most of your Atlantic hurricane, about 90%, that occurs from August to October. And on average by August 15 the Atlantic has one hurricane. So if you move the season back to May 15 you would go about three months on average with only one hurricane.

I guess the question is, are you trying to encompass actual hurricanes or are you trying to also encompass these weaker potentially short-lived storms? So there's kind of arguments both for and against it.

But I think one of the challenges — if we do move it back two weeks and the hurricane season still on average only has one hurricane through mid-August —is how long can you keep the public engaged?

We do all this messaging prior to the start of the hurricane season. The hurricane season is coming and people get jazzed up, ready to go, then the hurricane season starts and not much happens usually for about two to two and a half months. It's how long can you keep the public engaged, I think is one of the big questions if we do formally extend hurricane season back to May 15.

RMN: There's the public policy part of the debate, but there's also the facts and the scientific part of it. Do you think the facts and the science support extending it?

Klotzbach: The hurricane season I guess was officially defined to be June 1 to November 30 back in 1965. But when they did that there wasn't a formal definition, like we want “X” percent of the hurricane season to fall between those dates. Because if that's the case then you can look and say, “Okay, scientifically is now that percentage of the hurricane season, do you now need to shift that back to May 15?”

We're actually working on a paper on that topic right now. And it does look like if you go back to '65 and say, here's what that encompassed then and how that would encompass now, from a scientific perspective you could argue that we shouldn't shift it back to May 15. But then again you have the public policy issue.

There's certainly going to be a lot of dialogue on that topic in the next, probably in the next year, and I think obviously in 2021. It remains to be seen if we get one or two storms prior to June 1, I think that would probably almost seal the deal, so to speak. But if say we don't get anything this year until July or August it might at least push that discussion off another year or two.


Part 2 of the discussion, focused on the structure of CSU’s model and the future of hurricane modeling, will appear tomorrow.

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