What Happened to the 2014 Atlantic Hurricane Season?

The 2014 Atlantic hurricane season has fallen into a slumber heading into the final days of the season's peak month. 

(MORE: Expert Analysis | Hurricane Central)

Through Sept. 22, only five named storms have formed so far this season. This is almost three named storms behind the average pace, according to National Hurricane Center climatology. Interestingly, however, the number of hurricanes (four) and major hurricanes (one) is right on par with the season-to-date average.

More recently, the 2009 hurricane season had only reached the "F" storm, Hurricane Fred, by the last seven days of September.

A better method of summing up hurricane season activity than simply counting storms utilizes the Accumulated Cyclone Energy, or ACE, index. This is calculated by adding each tropical storm or hurricane's wind speed through its life cycle. Long-lived, intense hurricanes have a high ACE index. Short-lived, weak tropical storms, a low ACE index. Summing up the ACE indices of each storm or hurricane will give you an ACE index for the entire season.

Through Sept. 22, the Atlantic season-to-date ACE is only half of average, according to meteorologist Erika Navarro with The Weather Channel. This follows on the heels of the least active Atlantic hurricane season (by ACE) since 1994.

Meanwhile, the eastern Pacific season has been hyperactive, with an ACE index 45 percent above the average-to-date.

"Only 1992 (19) and 1985 (20) have had more eastern Pacific named storms through September 23 than 2014's 16 named storms," says Michael Lowry, hurricane specialist with The Weather Chann

(MORE: Weather Underground's ACE page)

Despite the quiet Atlantic season, we had Hurricane Arthur, the first U.S. landfalling Category 2 hurricane since Ike in 2008 and the earliest-in-season North Carolina hurricane landfall on record. Quiet hurricane seasons still produce impactful hurricanes, a point made frequently by Stu Ostro, senior meteorologist with The Weather Channel. The 2014 season was the first since 1983 the first three named storms all became hurricanes. (Note: This also happened in 1992, but there was an unnamed April subtropical storm added to the list, upon further review.)

Hurricane Edouard become the first Category 3 hurricane in the Atlantic basin since Sandy did so briefly in October 2012.

Suppressing Factors

One prominent suppressing factor so far this season has been wind shear, namely, the change in wind direction with height.

When wind shear is sufficiently high, thunderstorms are displaced from the center of a tropical cyclone, either weakening the cyclone or preventing it from becoming organized in the first place.

As the graph provided by Lowry below illustrates, wind shear over the main development region (Caribbean Sea and tropical Atlantic Ocean from the Windward Islands to the west African coast) from June through August 2014 was the second highest on record for that three-month period. 

This June-August wind shear was particularly strong over the Caribbean Sea. It's no coincidence that only one of the five named storms so far (Bertha) managed to hold together as a tropical cyclone anywhere in the Caribbean Sea.

Secondly, the atmosphere's temperature and moisture profile has tended to suppress the very thunderstorms needed to both develop and maintain tropical cyclones.

The black trace in the graph below indicates average atmospheric instability over a strip of the tropical Atlantic Ocean from just east of the Lesser Antilles to west Africa over the year.

By instability, we mean the degree to which the temperature and moisture profile of the atmosphere favors rising motion, forming clouds and thunderstorms. The higher the values on the graph, the more instability.

The blue trace below represents the actual instability so far in 2014, which has trended well below average. 

Advertisement

This means the tropical Atlantic atmosphere has been more stable, more suppressive of thunderstorms.

A more stable, suppressive atmosphere has also tended to be in place over the Caribbean Sea, but not as often near the U.S. East Coast, where three of the season's four hurricanes have tracked.

Still a Threat This Season

This doesn't mean we can simply mail in the 2014 Atlantic hurricane season.

An average Atlantic season will generate another five named storms, two hurricanes, and at least one major hurricane from late September through November.

October U.S. hurricane landfalls are not frequent. However, Wilma (2005) and Sandy (2012), two of the five costliest hurricanes in U.S. history, both recently wreaked havoc in October. 

The October hot spots for development shift back to the western Caribbean, the eastern Gulf of Mexico and near the U.S. East Coast. 

Given typical upper-level winds, disturbances in the western Caribbean have an increased chance of being pulled toward the U.S. in October.

South Florida has been struck by more hurricanes in October than any other month. 

The bottom line here is don't let your guard down. If you haven't already, get your hurricane kit together, find out if you're in an evacuation zone, and don't fall for the common hurricane myths that could put you in danger.

Prepare now, before a hurricane threatens.

MORE ON WEATHER.COM: NASA's Best Hurricane Images