Tag Archives: Hurricane Season

Why is this year’s hurricane season so much worse?

It isn’t. Well, it is a little, but not totally. OK, it is, but actually, it is complicated.

First, you are probably asking about the Atlantic hurricane season, not the global issue of hurricanes and typhoons and such. If you are asking world-wide, recent prior years were worse if counted by how many humans killed and how much damage done.

With respect to the Atlantic, this was a bad year and there are special features of this year that were bad in a way that is best accounted for by global warming. But looking at the Atlantic hurricanes from a somewhat different but valid perspective, last year was worse (so far) and this year is ordinary, within the context of global warming. So, let’s talk about the global warming question first.

How Global Warming Makes Hurricane Seasons Worse

The effects of global warming on hurricanes in the Atlantic have two interesting features that must be understood to place this discussion in proper context.

First, we are having a bunch of bad decades in a row probably because of global warming. If we compare pre-1980, for a decade, with post 1980, or pre vs. post 1990, or anything similar, the more recent years have had more hurricanes than the earlier years. Comparing to even earlier time periods is tricky because of differences in available data (Satellites make a difference, probably, even with giant weather features like hurricanes). This is mainly due to increasing sea surface temperatures, but there are other factors as well.

Hurricanes are more likely to form when sea surface temperatures are higher. Higher sea surface temperatures can make a hurricane larger or stronger. Hurricanes will last longer if there is more, higher, hurricane-hot sea to travel over. If sea surface temperatures are high enough to cause hurricanes earlier in the year or later in the year, the hurricane season can be longer. Possibly, storms that in a non-warmed world would not have made it to “named storm” status are moved to that level of strength and organization because of the elevated sea surface temperature.

Sea surface temperature increases of small amounts cause large changes in hurricanes, and large changes in hurricanes cause larger changes in potential damage level. The increase in Atlantic sea surface temperatures over recent decades have probably been sufficient, according to my thumb-suck estimate that I strongly suspect is close to correct, to make about half the hurricanes that would have existed anyway jump up one category. Then, when hurricanes get stronger, the amount of damage they can do goes up exponentially. So the sea surface temperature increases we’ve see with global warming easily explain the fact that we’ve had more hurricanes overall, and stronger ones, over the last twenty or thirty years than during the previous years back to when the data are still pretty good.

Second, the science says this will get worse. There is one 2007 study (by Vecci and Soden, in Geophysical Research Letters) that suggests that maybe in the Atlantic, smaller size hurricanes will be less likely to form because of increased vertical wind shear, but that study does not mean much for larger or stronger hurricanes. This decade old study is constantly cited as evidence that global warming will not increase hurricanes in the Atlantic. Other studies show that the overall amount of hurricane activity, and the potential higher end of hurricane strength, and the size, and the speed at which they form, and the amount of water they can contain, and possibly the likelihood of a hurricane stalling right after landfall, go up. Up. Up. Up. One study says down and that word, “down” it resonates across the land like a sonic boom. The other studies say we can expect, and to varying degrees already see, up, up, up, up, up, and denial makes words like “up” and “more” and “worse” and “exasperated” dangerously quiet. Please don’t fall into that trap. Oh, by the way,the one study that says “down” has not been replicated and though experts feel it has some merit, it is far from proven and there are reasons to suggest it my be problematic.

Comparing the 2017 Atlantic Hurricane Season to Other Years

Funny thing about hurricanes: They exist whether or not they menace you. Every year a certain number of hurricanes (usually) form and wander about in the Atlantic ocean for a while, maybe hitting some boats, but otherwise doing little more than causing some big waves to eventually reach beaches in the Caribbean or the eastern US.

This year, we’ve had four major hurricanes so far. Harvey, which maxed out as a Cat 4, ravaged and flooded Texas and Louisiana. Irma, maxing at Cat 5, ravaged Florida after wiping out islands in the Leewards and doing great damage to Cuba and elsewhere in the Caribbean. Maria, maxing out as a Cat 5, did major damage in the Leewards and notably wiped out Puerto Rico. So, four Major Hurricanes formed in the Atlantic and hit something major.

Meanwhile, Jose, another Major hurricane at Cat 4 status, still spinning about in the North Atlantic, is one of those that hit nothing. And that’s all so far this year.

Last year, there were almost exactly the same number of named storms in total (so far) and just like 2017, 2016 had four major hurricanes.

You remember Matthew, which scraped the Atlantic coast and was rather damaging. But do you remember Gaston (Cat 3)? Nicole (Cat 4)? Otto (Cat 3)?

Gaston and Nicole wandered about in the Atlantic and hit nothing. Otto was for real, it hit Central America, but not the US, so from the US perspective, it counts as a non-hitting hurricane. Also, it was only barely cat 3 and weakened quickly.

From 2000 to 2016, inclusively, we have had an average of 15 named storms per year, with a minimum of 8 and a maximum of 28, with most years being between 10 and 16. So far 2017 has had 13 named storms. We may have a couple more. So, likely, we will be right in the middle.

For the same period, the number of hurricanes has ranged from 2 to 15 with an average of about 7. This year, we have had … wait for it … 7. We may or ma not get another one, not very likely two more. In other words, this is an average year for the number of hurricanes.

For the same period, the number of major hurricanes ranges from 0 (though only one year ad zero, it is more typical to have 2 in a low year) to 7, but again, 7 is extreme. It is usually from 2-5. The average is just over 3. This year, we have four. That’s pretty typical.

So, within the context that the last couple of decades has had a somewhat higher than average frequency of hurricanes, and probably more strong ones than previous decades, this we had a typical year this year.

Why does it feel different? Why is it in fact difference, with respect to the horror of it all? Because we had more landfalls, and more serious landfalls.

Keep in mind that Harvey could have hit Houston differently and done more damage. Keep in mind that Cuba beat up Irma, then Irma failed to strike Florida in just the right way to do maximum damage. Keep in mind that after wiping out Puerto Rico, Maria swerved quickly out to sea. In other words, keep in mind that this year could have been much worse than it was.

This is the point that you must understand: Any year can be like this year, or worse. And, with increasing sea surface temperatures and other global warming related factors, worse still.

Will there be a lot of hurricanes in 2013?


The Tropical Meteorology Project at Colorado State University makes annual predictions of hurricane season activity, and they released one of these predictions today. This particular group has a good track record, although I would worry that they tenaciously hold to the idea that global warming is not a factor in hurricane development despite the fact that some of the factors (a disrupted ENSO and high SST) that are most affected in the Atlantic by global warming actually drive their predictions. Still, their predictions seem to be based on good empirical data and are probably robust. (Other season forecast information is to be found below).

El Nino conditions tend to reduce hurricane activity, and the warmer the waters in the North Atlantic, the more likely hurricanes are to form from tropical depressions, the stronger they are likely to be, and the longer they are likely to last.

This year, El Nino conditions are unlikely to develop, and sea surface temperatures in the North Atlantic are unusually high as they have been for a few years.

The TMP has released this PDF of their report, which states:

We anticipate that the 2013 Atlantic basin hurricane season will have enhanced activity
compared with the 1981-2010 climatology. The tropical Atlantic has anomalously
warmed over the past several months, and it appears that the chances of an El Niño event
this summer and fall are unlikely. We anticipate an above-average probability for major
hurricanes making landfall along the United States coastline and in the Caribbean.
Coastal residents are reminded that it only takes one hurricane making landfall to make it
an active season for them, and they need to prepare the same for every season, regardless
of how much or how little activity is predicted.

TMP predicts that there is a 72% chance of at least one category 3 or above hurricane landing somewhere on the US coastline (the average probability over the last century is 52%). There is a 48% of such a landfall along the Atlantic coast plus Florida not counting the panhandle (compared to the century average of 31%) and a 47% probability for the Gulf Coast on the Florida Panhandle and points west to Brownsville (compared to 30%). The chance of at least one category 3 or stronger hurricane hitting points in the Caribbean is 61% (compared to 42%).

The forecast predicts that there will be 18 named storms active over 95 days, of which 9 will be hurricanes, active over 40 days, of which 4 will be Category 3 or above.

The Weather Channel is saying the following about the 2013 season:

The Weather Channel released its first 2013 Atlantic hurricane season outlook on April 8, 2012, calling for another active season.

The forecast calls for a total of 16 named storms, 9 of which are expected to become hurricanes, including 5 major hurricanes (Category 3 or higher on the Saffir-Simpson Hurricane Wind Scale).

These forecast numbers are above the long-term average from 1950-2012 (12 named storms, 7 hurricanes, 3 major hurricanes) and slightly above the averages for the current active era from 1995-2012 (15 named storms, 8 hurricanes, 4 major hurricanes).

The Weather Company’s WSI says this:

Weather Services International (WSI) expects another active tropical season this year, with 16 named storms, nine hurricanes, and five intense hurricanes expected (16/9/5). This compares to the 1950-2012 normals of 12/7/3 and the more recent “active period” (1995-2012) normals of 15/8/4.

Researchers at UCL, UK (PDF) predicts 3-4 “intense hurricanes” out of 7-8 hurricanes with 15-16 tropical storms:

The TSR (Tropical Storm Risk) April forecast update for Atlantic hurricane activity in 2013 continues to
anticipate an active hurricane season to moderate probability. Based on current and projected climate
signals, Atlantic basin tropical cyclone activity is forecast to be about 30% above the 1950-2012 longterm norm but slightly below the recent 2003-2012 10-year norm. The forecast spans the period from 1st
June to 30th November 2013 and employs data through to the end of March 2013. TSR’s two predictors
are the forecast July-September trade wind speed over the Caribbean and tropical North Atlantic, and the
forecast August-September 2013 sea surface temperatures in the tropical North Atlantic. The former
influences cyclonic vorticity (the spinning up of storms) in the main hurricane track region, while the
latter provides heat and moisture to power incipient storms in the main track region. At present, TSR
anticipates both predictors will have a small enhancing effect on activity.

Weather Underground’s MAweatherboy1 posted this last month:

I foresee a season that will see near to above average activity. One of the main factors we look at to determine this is the ENSO, which involves the temperature of waters in the Pacific Ocean. Warm Pacific waters, called El Nino if the anomaly is greater than 0.5 degrees Celsius, tend to suppress activity in the tropical Atlantic, while cooler than average Pacific waters, called La Nina if the anomaly is greater than 0.5 degrees Celsius, tend to enhance activity. … This year, I am expecting a very neutral ENSO, with average, season-long (June 1-November 30) Pacific water temperatures that are in the key regions likely not averaging more than 0.2 degrees Celsius above or below average, although I would favor the cooler end of that range if anything. The Southern Oscillation Index (SOI) is an important component in determining ENSO. Positive SOI values promote cooler Pacific waters, and vice versa. SOI values have been mostly negative this winter, though not by much, and I do not foresee any huge changes in this. Neutral conditions like this tend to promote near normal, or in some cases above normal activity. The record breaking 2005 hurricane season was primarily influenced by neutral ENSO conditions.

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