Atlantic Hurricane Season Recently Sprung To Life And The MJO Is Partly To Blame

A​tlantic hurricane season sprung to life with four named storms forming in a couple of days, and it's partly related to a forecast factor meteorologists track that you might not have heard of before: the MJO.

T​he boom of tropical storms across the Atlantic isn't entirely uncommon: This burst of activity is called a tropical cyclone outbreak, which is defined as having three or more tropical storms or depressions form within a few days of one another in a relatively short amount of time in close proximity of each other.

I​n this case, we saw four tropical storms develop in 39 hours, including Gert, Emily, Franklin and Harold. It's the shortest span of time on record that four storms have formed in the Atlantic, according to Dr. Phil Klotzbach, a tropical scientist at Colorado State University.

B​lame the MJO for the outbreak of storms: One of the mechanics behind bursts of activity like this one is called the Madden-Julian Oscillation, or MJO.

In short, there is a disturbance at the top of the atmosphere that can cause upward motion in the atmosphere. When this upward motion is enhanced over a given spot, thunderstorm activity in the tropics gets an assist and makes the possibility of tropical storms forming more likely.

S​uch bursts of activity are most common in August and September when lower-atmospheric conditions such as wind shear and humidity are usually more favorable for development. Water temperatures are also typically at their warmest.

H​ere's where the MJO wave came from: This wave of activity travels around the globe in an eastward direction and makes that trip in about 40 days.

T​his particular MJO wave actually began closer to Asia a couple of weeks ago with the start of typhoons Doksuri, Khanun and Lan. It also assisted in the development of hurricanes Dora, Fernanda and Hilary, and also Tropical Storm Greg in the East Pacific Ocean.

T​ropical waves are elongated areas of low pressure that are often the seeds for the formation of many tropical depressions and tropical storms. But, these waves need thunderstorm activity to flourish in order for them to organize into storms.

(​MORE: Tropical Waves Explained)

W​ind shear has been an opposing factor for some of the storms: While there has been a burst of storms in the Atlantic, wind shear has been a factor that has prevented them from intensifying much.

E​mily lasted about 24 hours in the eastern Atlantic. Gert in the western Atlantic and Franklin in the eastern Caribbean were both poorly organized because of wind shear as of Tuesday morning.

Wind shear is the change in wind speed and direction with height. It's a hostile factor that can rip apart tropical storms.

(​MORE: How Wind Shear Can Affect Tropical Storms)

Chris Dolce has been a senior meteorologist with weather.com for over 10 years after beginning his career with The Weather Channel in the early 2000s.

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