Where are all the Atlantic hurricanes?

Friday, September 19, 2014, 1:03 PM - I’m all set up and ready to go intercept a hurricane, but the only one I've managed to get into was a rapidly weakening Hurricane Arthur in Nova Scotia on July 5, 2014.

Question: Where are all the Atlantic hurricanes?

The record for the most time between a major (Category 3 on the Saffir-Simpson scale) hurricanes to make landfall in the United States has been obliterated. The last one to strike was Wilma in 2005 when it slammed into Florida on October 24 of that year. There have been a few devastating hurricanes to make landfall since ’05, with the most famous being Sandy (which actually wasn't a true hurricane when it hit New York). But by definition, no major hurricanes in nine years.

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So what’s going on?

The answer is complicated, and not as satisfying as I’d like.

First off, we have to determine a scientific baseline for measuring hurricane activity and counting the number of storms that occur each year doesn't always work well.

Here’s why:

Measuring a hurricane season strictly by the number of storms or the impact of those storms isn't the best way to determine an active season. We can easily over - or under - estimate activity by looking strictly at storm numbers. Imagine a season that had massive, powerful hurricanes, but only two in number. Contrast that with a season with lots of weak tropical storms that barely registered a dent on top of getting a few people wet. A simple count might lead you to the conclusion that the second season was the more active, which might not be true.

Instead, meteorologists use something called Accumulated Cyclone Energy, or ACE. It’s a measure of the power and longevity of the individual storms in a given season.

HURRICANE ARTHUR:

From Weather Underground:

The ACE is calculated as the square of the wind speed every six hours, and is then scaled by a factor of 10,000 for usability. The ACE of a season is the sum of the ACE for each storm and takes into account the number, strength, and duration of all the tropical storms in the season (Shown as the vertical number in the chart below).

In looking back to 1970, a picture of what’s going on in the Atlantic in terms of ACE emerges:

Hard to pinpoint a trend.

The reason I use 1970 as a starting point is that satellite observations, etc., ensure that a pretty good handle on every storm spinning out there over the Atlantic. There’s a slight upwards trend, but even then, without applying some rigorous stats to it, a particularly good fit with a trend just isn't there.

Also, variations between seasons are really dependent on what’s going on in the atmosphere. And, remember to address an important part of the globe: the Pacific Ocean. Add the huge contribution (56 per cent to the Atlantic’s 13 per cent) of Pacific ACE, everything flattens out to show no upward or downward trend in the ACE from 1970.

In short, slow seasons are followed by active seasons, the Atlantic gets active, while the Pacific gets quiet, and so on. As mentioned above, the fact that a major hurricane hasn't made landfall in the U.S. is due to couple of factors; overall wind patterns steering the storms out to sea, the lack of storm formation close to land (and luck!). More on it later.

For the last couple of years, an persistent east coast troughing has steered many of the hurricanes away from land and out to sea or pulled them north into colder waters (thus weakening them before they do make landfall). Storms have also been tending towards forming well away from U.S. and Canadian shores. This lessens the chance to make landfall.

Finally, there’s that ever present luck factor (if you believe in that). My opinion: probability has more to do with it than luck. The period that we’re looking at is too small to make a significant conclusion and eventually, we will see another major hurricane make landfall. If we take a long enough period of time and check the stats, the lack of landfalls in the last 10 years is balanced out by the hyper land-falling years like 2004 and 2005.

It all balances out in the end and unless we see a major change in the geography or climate of the planet (like the continent of Africa deciding that it needs a nice Asian vacation), major hurricanes will begin making landfall in the U.S. again.

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