With one month to go, it looks like this year's Atlantic Hurricane Season will go down as the least active season in seventeen years. Here are five graphics that show how such a quiet hurricane season managed to be so interesting.
Forecasters correctly predicted a below-average season in the Atlantic this year, but assuming that no other storms form beyond today, they underestimated just how quiet the season would be. Through yesterday, the 2014 Atlantic Hurricane Season has produced eight named storms, six of which became hurricanes (which is above average) and two of those hurricanes became major hurricanes (which is below average).
We've had a total of nine tropical cyclones and only eight named systems this year, making this the quietest hurricane season in the Atlantic since 1997. Not that that's a bad thing, of course. The strength distribution of the cyclones that formed this year is impressive, with at least one of every type of storm from a tropical depression up through a category four hurricane.
Let's compare this to last year's activity.
2013's Atlantic Hurricane Season saw fifteen cyclones develop—twelve of which were tropical storms, two hurricanes, and one only made it to tropical depression status. Even though the season was above average in terms of named systems, the season fell far below average in that only two low-end hurricanes formed.
This year's storm tracks followed those commonly seen in the Atlantic, with storms forming in the lower latitudes and sharply recurving to the northeast as they climb poleward.
Even though it was a relatively quiet year, five of the eight storms that formed this year—Arthur, Bertha, Dolly, Gonzalo, and Hanna—wound up making landfall in areas ranging from the Windward Islands to North Carolina. The worst storm in the Atlantic this year was Hurricane Gonzalo, which made a rare direct landfall in Bermuda earlier in October as a strong category two storm.
The National Hurricane Center also keeps track of the tropical storm force and hurricane force wind swaths produced by each storm, which The Vane has compiled into one map. Areas shaded in orange experienced tropical storm force winds (39-73 MPH) from at least one storm, while areas in red experienced hurricane force winds (74+ MPH).
Why is this year so quiet?
This year's hurricane season in the Atlantic was (and continues to be) quiet largely due to enhanced wind shear and destructive amounts of dry air. Wind shear in the upper-levels of the atmosphere can rip the tops off of thunderstorms that attempt to form into a tropical cyclone, killing the storms and preventing tropical systems from organizing. Dry air has a similar deadly effect on tropical cyclones, preventing thunderstorms from forming and, when ingested into the core of a tropical system, can very rapidly kill its thunderstorm activity and thereby cause the cyclone to dissolve.
What about the Pacific?
The eastern Pacific, on the other hand, is seeing its most active season in more than twenty years. We often don't hear about hurricanes that form in the eastern Pacific since they often move out to sea, and to be quite honest, these storms often impact areas of southwestern Mexico. American media doesn't spend much (if any) time covering disasters outside of the United States, so many people just don't hear about or pay attention to these storms.
The eastern Pacific has seen twenty-one named storms this year, fifteen of which formed into hurricanes and nine of those turned into major hurricanes. The worst storm of the year was easily Hurricane Odile, which caused extensive damage to Cabo San Lucas and surrounding cities on the southern tip of the Baja Peninsula.
There is still time for storms to form in the Atlantic basin before the year is out—hurricane season doesn't officially end until November 30, and while unlikely, storms can and have formed during the month of December. Storms that form this time of the year often form in the Caribbean or the Gulf of Mexico, so coastal residents from Texas to Florida shouldn't let their guards down yet.
[Images: satellite image of Hurricane Arthur via NASA/GOES, all others by the author]