The Intersection

What Was Kyrill?

i-35694b9fb5836c2d5152e81a45273bc5-Kyrill Waves.jpg

[Huge waves slam the port city of Wimereux in Northern France.]

Last week I griped about how various media organizations were calling the large scale cyclonic system that slammed Europe a “hurricane.” In this post, I’d like to be a bit more positive and look more closely at this weather phenomenon that was dubbed “Kyrill.” (Not Hurricane Kyrill.)

The storm had a central pressure that dropped down as low as 964 millibars, according to Wikipedia (which I’m relying on because I can’t read German). That helped produce winds as strong as 125 miles per hour. I’m not sure if these are gusts or sustained winds, but either way, that’s well past the threshhold of hurricane strength. Category 3 hurricanes have sustained winds between 111 and 130 mph. No wonder Kyrill drove huge waves and brought devastation and even a few dozen deaths.

Given such attributes, it’s perfectly legit to say that Kyrill had winds of “hurricane force” or “hurricane strength.” But of course, this was an extratropical cylcone–a storm driven by north/south temperature contrasts between air masses–and not a hurricane. In Europe these storms, at their most powerful, are also called windstorms. The German word is apparently “orkan,” which leads to definitional confusion and to some people using the word “hurricane” after translation. Names for different types of storms seem to overlap in German; “orkan” can apparently mean both “hurricane” as well as “winter gale” and “winter storm.”

Technically, however, European windstorms are very different than hurricanes, though they can also become very powerful. Still stronger than Kyrill was the Great Storm of 1987, with a pressure fall down to 958 millibars.

What all of this goes to show is that there is considerable overlap, both in terms of their manifestations and in terms of their effects, between hurricanes (tropical cyclones) and extratropical cyclones. There’s no doubt that tropical cyclones can become considerably more powerful than extratropical ones, at least in the deep tropics. There’s no doubt that the pressure falls in the most extreme tropical cyclones are much lower than in the most extreme extratropical ones.

Both types of storms, however, can produce winds upwards of 100 mph and areas of very low pressure. Just imagine being an 18th or 19th century weather watcher off, say, the coast of Boston, and trying to tell the difference between one type of storm and the other. You wouldn’t have a clue.

Our ability to distinguish between types of cyclones is a product of the era of radar and satellite meteorology. When the media dubbed Kyrill a hurricane, by contrast, they were hearkening back to a much earlier era, when words like “storm,” “gale,” “hurricane,” and so forth were used far more interchangeably. Journalists really ought to be more up to speed on the state of the science; but their confusion is in some sense not just understandable but, indeed, grounded in both etymology and history.

Comments

  1. #1 bigTom
    January 22, 2007

    Then you have the phenonena of tropical cyclones making the transition to extra-tropical cyclones. I.E. a hurricane often merges
    with frontal system(s) as it reaches the higher latitudes.

  2. #2 Mark UK
    January 22, 2007

    The winds were not sustained but gusts… I lived in Germany for nearly a year and only ever heard “orkan” used to describe a hurricane. Alternatively it was used to point out that the expected winds will have gusts of hurricane strenght. I think the word cyclone confused a few people…

  3. #3 llewelly
    January 22, 2007

    If you visit my favorite ESRL link you can see the area over the Arctic Circumpolar Current has average sea level pressue of about 990 mb year round. It has many strong extra-tropical cyclones. Unfortunately I don’t know how strong. The GFS and the other models show cyclones below 960mb like this at least once a week, but I don’t think modeled cyclone pressures are high quality estimates. The wikipedia page on extra tropical cyclones mentions a 928 mb cyclone that passed between Greenland and Iceland – but I suspect the ACC does better.

  4. #4 George
    January 23, 2007

    Storms such as Kyrill occur here in the Northwest as well. Though storms as strong as Kyrill are not frequent here in the Northwest or in Europe. There are many more that have the impact comparable that of cat 3 hurricanes on costal and inland towns. Here is a reference to a site that has some data on the history of such storms in the Northwest.

    http://oregonstate.edu/~readw/

    Cheers
    George

  5. #5 Kristen
    September 9, 2008

    I’ve been looking for an image of Kyrill to use in a piece of marketing collateral I’m working on and this one is perfect. Can you please direct me to where you found it so I can request permission to use it? Thanks in advance. Great article. I will be back, I’m sure.
    Best,
    Kristen

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