This Saturday is the climatological peak of hurricane season in the Atlantic Ocean. It’s been a weird year with about seven storms so far, and we still have more than two months until it’s over. The season could have been worse if it weren’t for El Niño conditions out in the Pacific Ocean, which saves the butt of many coastal residents around the Atlantic during this time of the year.
El Niño usually has the same effect on tropical cyclones in the Atlantic Ocean that walking into a wood chipper has on your body. The results aren’t pleasant (for the storm), but this basin is nothing if not tenacious. Tropical activity so far this year is slightly above average from where it should be on September 8, though that’s not saying much about the seven storms we’ve seen since May.
You’re probably just as sick of hearing about El Niño as I am. Like it or not, the abnormal warming of the waters in the eastern equatorial Pacific Ocean can have a dramatic effect on the weather we see around the United States, and one of the most obvious impacts is its deep-sixing of tropical activity in the Atlantic Ocean.
We’re in what is probably going to be looked back on as a significant (if not historic) El Niño right now, with sea surface temperature anomalies between +1°C and +2°C in the eastern Pacific. You can see the warming in the map at the top of this post, displayed by the awesome Earth feature at nullschool.net.
El Niño is known to produce abnormally strong wind shear over the Caribbean, Gulf of Mexico, and Atlantic Ocean during the summer months, which acts like a guillotine to any tropical cyclone that tries to bubble up. Wind shear tears the tops off the thunderstorms and displaces convection that survives far away from the center of a storm’s circulation, preventing the system from strengthening and organizing, causing them to floof apart into nothing.
It’s pretty likely that the abnormally strong wind shear over the Atlantic basin right now is linked in part (or wholly) to the strong El Niño present over the eastern equatorial Pacific right now, so it’s not too surprising that any storms that manage to develop are getting torn apart before they can make it beyond the Caribbean.
Here’s a look at each of the seven storms that have formed in the Atlantic Ocean so far this year. It’s not teeming with cyclones like the Pacific, but this map has started to fill in pretty quickly in recent days. Four of those seven storms developed within the past three weeks, with one of them—Grace—ongoing as of the writing of this post. Though it’s been quiet, each of these storms has been interesting in its own right.
Ana became a tropical storm off the coast of South Carolina early in May—a month before the start of the hurricane season—triggering the usual “ARE WE IN FOR A HORRIFIC HURRICANE SEASON!?” scarelines you come to expect from local news stations and the viral content producers employed by your omnipresent email provider. The storm came ashore near Myrtle Beach, becoming the second-earliest we’ve ever seen a tropical cyclone make landfall in the United States.
A little more than a month later, Tropical Storm Bill took shape off the coast of Texas, producing flooding rains as it slowly made its way through the southern Plains and Midwest. Though it’s not reflected by the National Hurricane Center’s track data I used in the map above, Bill remained a tropical depression over land for an astounding four days before finally falling apart in Ohio.
Hurricane Danny was a very tiny storm, and its small size allowed the storm to overcome the lethal effects of dry air and wind shear in order to rapidly intensify into a category three hurricane with maximum winds of 115 MPH. Its tiny stature being the same flaw that allowed it to thrive, Danny fell apart as it crossed the Leeward Islands.
Danny (above) marked the beginning of a train of tropical waves that chugged off the African coast, four of which went on to become cyclones as of September 8.
Tropical Storm Erika followed closely behind Danny, somehow holding itself together in an unfavorable environment, making it all the way to Haiti before petering out. Had the storm managed to strengthen, it was forecast to come close to Florida as a hurricane, but it never made it that far. Disorganized as it was, the storm produced extensive flooding and landslides on the small island of Dominica, killing dozens of people and causing enough damage to “set the island back twenty years,” according to the country’s prime minister.
Hurricane Fred is probably the most interesting storm we’ve seen this year. Fred became a hurricane at 22.5°W—just southeast of the Cape Verde Islands—becoming the farthest east we’ve ever seen a hurricane form in the tropical Atlantic and the second-farthest east we’ve ever seen a hurricane form anywhere in the Atlantic. 2005’s Vince holds the latter record, as it formed a few hundred miles southwest of Spain.
Tropical Storm Claudette was interesting but brief—forming from a complex of thunderstorms along a decaying cold front moving off the Mid-Atlantic coast—and Tropical Depression Grace is a forgettable system in the middle of nowhere that’s on the cusp of dissipating as of this post.
An “Average” Season
Hurricane seasons can vary wildly from one to the next, with some years producing a bunch of storms while others can go a month or longer without seeing even a hint of a disturbance. When you average out all of the hurricane seasons we’ve seen in recent decades, the Atlantic does stay hopping during the warm months. The basin typically sees twelve named storms, six of which become hurricanes, and three of those hurricanes grow into major hurricanes (category three or higher).
If a year stays right on average, we’ll make it up to the “L” storm (#12) by November, and most seasons do come within one or two storms of that average. Averages are the product of all extremes, though, so some years go bonkers while others limp along with barely a puff.
The most active season on record was 2005, which saw an incredible 28 named storms. Six of those 28 storms were named after Greek letters (Alpha, Beta, Gamma, Delta, Epsilon, and Zeta) because we ran out of names on the English alphabet. That last storm—Tropical Storm Zeta—formed on December 30, 2005, and kept right on going through January 6, 2006.
The 1992 hurricane season—the year of Andrew—was a below-normal season that bloomed rather late. Andrew didn’t form until the end of August, and five of the year’s seven named storms all formed during one nine-day span between September 17 and September 26.
Long-term outlooks are notoriously hard to nail accurately, and they’re a bit unsettling since predictions of “below-average activity” can lead to a sense of complacency.
This past spring, every organization that issues long-term seasonal hurricane outlooks predicted a below-average season, with forecasts expecting anywhere from six to eleven named storms to take shape before the crushing influence of winter sends the Atlantic into hibernation.
We’re at seven so far, and there’s a chance that we could see number eight—which would be Henri—form near Bermuda over the next day or two. Assuming (correctly or not) that we don’t see another named storm form between now and the time nature flips the switch to winter, we’d stay below-average but within what was forecast.
However, sheer numbers are only part of the story.
The simple number of storms that form doesn’t tell you much. 15 tropical storms could form in one summer, but if they all had maximum winds of 45 MPH and lasted a day before dissipating, they could have all produced less combined energy than a major hurricane produces in twelve hours.
One of the best metrics to use when studying the intensity of a hurricane season is called Accumulated Cyclone Energy, or ACE. Meteorologists calculate ACE by looking at the tropical cyclone’s sustained wind speed (in knots) every six hours for the duration of its life. Storms that are longer-lived and have higher winds will result in a higher ACE. Powerful storms like Hurricane Ivan can have a lifetime-total ACE as high as 70, while very weak storms (like T.D. Grace above) can have an ACE value of just one or two.
You can add each storm’s ACE value together to arrive at a season’s score, and use this value to compare the strength of one season to another. Between 1981 and 2010, the average yearly ACE value for the Atlantic Ocean was 104. The Atlantic season with the highest ACE was 2005—clocking in at 250—while a quiet season like 2013 had an ACE of just 36.
So far, even though we’re slightly ahead of average in the named storm game, the year’s ACE is just half of what it should be by this point in the year. All seven storms in the Atlantic have produced a combined ACE of 24.6, and the year-to-date average is 46. A quick look at the season’s ACE shows you that, overall, the storms this year have been weak and short-lived.
Don’t Let Your Guard Down
It’s likely that we’ll see a couple more storms before the season is out. Even though it’s a quiet and unfavorable year, there’s always the chance that a system could threaten the United States. Even a weak tropical storm is dangerous if it produces extensive flooding rainfall or tornadoes—one of the worst storms last decade was Tropical Storm Allison, which killed dozens of people in the flash flooding that resulted from several feet of rain falling in a short period of time.
Prepare for the worst, but hope for the best. Winter is coming—hopefully we can delay the inevitable for at least another year.
[Top Image: Sea surface temperature anomalies, via earth.nullschool.net | Season Map: author | Storm Count Chart: NHC | Outlook Chart: author | SST Map: NOAA | Corrected after publication for clarity.]