The 2017 Atlantic hurricane season is shaping up to be the busiest in a decade.

So far this year, there have been 13 named tropical storms. It is a family role call getting ever-longer: Arlene, Bret, Cindy, Don, Emily, Franklin, Gert, Harvey, Irma, Jose, Katia, Lee and now Maria.

And there are still two months to go until the end of the season.

The average for any given year is 12 named storms, of which six become hurricanes, including three major ones. A major hurricane registers above category 3 on the Saffir-Simpson scale.

Image: NOAA

Axios, using data from the National Oceanic and Atmospheric Administration, has plotted every Atlantic storm since 1987. You can view their interactive chart here.

Each line represents the life of a storm, with those coloured red a category 5. The higher the line, the higher the recorded wind speed.

It shows that Irma reached maximum speeds of 184 miles per hour. Previously, only hurricane Wilma in 2005, and hurricane Gilbert in 1988 had reached these speeds.

Before this season, other than Matthew in 2016, there has been no category five hurricanes at all since Dean and Felix struck in 2007.

Image: Axios

This year’s hurricanes

Image: WMO

Irma and Maria were both category five hurricanes, hitting the Caribbean the hardest and causing widespread devastation. It is exceptionally rare to have two category 5 hurricanes in such a short space of time and on such a similar track.

The last time two major hurricanes arrived in quick succession was in 2005, when Katrina and Rita wreaked havoc on the Gulf Coast. There were two other category five hurricanes that year.

Breaking records

Hurricane Irma, as well as causing devastation in low-lying Caribbean islands, also broke records.

It generated the most Accumulated Cyclone Energy - a measure of the storm's intensity - on record in the Atlantic. It also generated more of this energy than the first eight named storms of the Atlantic hurricane season combined.

It reached maximum winds of 185 mph for 37 hours – the longest any recorded cyclone around the globe has maintained that intensity.

Maria is the third hurricane of category 4 or above to make US landfall in the same season, unprecedented in the modern era.

Abnormal hurricane season

Back in May, National Oceanic and Atmospheric Administration predicted an above-normal Atlantic hurricane season - the period from June 1 through to November 30.

Image: NOAA

The forecasters blame the increased hurricane activity on the lack of El Niño this year. El Niño is an ocean phenomenon characterised by unusually warm ocean temperatures in the Equatorial Pacific.

Strong El Niños, along with something called wind shear, typically suppress the development of Atlantic hurricanes.

Wind shear refers to the change in wind speed and direction between roughly 1,500 - 10,700m above the ground. Strong vertical wind shear can rip a developing hurricane apart, or even prevent it from forming.

The NOAA said that their forecast: “reflects our expectation of a weak or non-existent El Niño, near - or above - average sea-surface temperatures across the tropical Atlantic Ocean and Caribbean Sea, and average or weaker-than-average vertical wind shear in that same region.”

Image: Climate.gov

What’s in a name?

Hurricanes are named so that they can quickly and easily be identified and warnings broadcast. Short names are easy to remember.

The names come from a prepared list, and are often used again. That’s unless a storm is so deadly or costly, that using the name again would be too upsetting.

Infamous storm names such as Haiyan (Philippines, 2013), Katrina (USA, 2005) and Tracy (Darwin, 1974) are good examples.

The UN has warned that, in the face of the ever-increasing impact of extreme weather events, even more efforts have to be made to boost resilience and strengthen damage mitigation measures.

Image: Weather.com

Secretary-General António Guterres said: “This year’s hurricane season fits a pattern: changes to our climate are making extreme weather events more severe and frequent, pushing communities into a vicious cycle of shock and recovery.”