At a Glance

Tropical development usually doesn't happen in June east of the Lesser Antilles.That's because dry air and wind shear is usually in place early in the season.The few times that has happened, though, tend to predict an active hurricane season.This has happened twice in the past five years.

A tropical storm could form east of the Lesser Antilles this week, and if it were to do so, it could be yet another sign that an active hurricane season is ahead.

Tropical storm development east of the Lesser Antilles in the tropical Atlantic Ocean is rare in June, even if a couple of recent active seasons have bucked that history.

Now the National Hurricane Center (NHC) is monitoring a disturbance several hundred miles east of the Windward Islands (the southern part of the Lesser Antilles) for possible development in the coming days.

Tropical storms typically don't develop over this strip of the Atlantic Ocean this early in the season because either strong wind shear and/or dry air keeps them from forming.

In the entire historical database, only four storms have formed in June east of the Lesser Antilles.

Only four storms dating to the mid-19th century have formed in June east of the Lesser Antilles.

(Data: NOAA/NHC)

However, two of those far east June storms have formed in the past five years, including what would later become last year and in 2017.

If this happens again this year, does this guarantee another active hurricane season?

How Those Four Hurricane Seasons Turned Out

You would think if the atmosphere was able to generate a tropical storm so early, in an environment typically quite hostile in June, that would clinch another hyperactive season.

So let's look a little deeper into the previous years that happened.

First, let's look at each season's ACE index. Short for Accumulated Cyclone Energy, this is a metric meteorologists use that not only counts the number of storms and hurricanes, but also takes into account how intense and long-lasting they are. Seasons with numerous, long-lasting, intense hurricanes have a high ACE. Those with few, short-lived, weaker storms have a low ACE.

Acknowledging we have a small sample size of only four previous years with June storms east of the Antilles, three of the four seasons ended up more active than average.

Two of those years - 1933 and 2017 - were among the seven most active hurricane seasons by ACE all-time, according to compiled by Phil Klotzbach from Colorado State University.

ACE index values for the four hurricane seasons which produced a June tropical storm east of the Lesser Antilles. The 30-year average ACE from 1991-2020 (122.5) is plotted as a vertical line.

(Data: NOAA/NHC, Phil Klotzbach (CSU); Graph: Infogram)

Those three active hurricane seasons each had at least 17 storms. Even the more inactive 1979 season managed to produce six hurricanes.

These active seasons also had something else in common: La Niña.

La Niña is the periodic cooling of the equatorial central and eastern Pacific Ocean water.

When this happens during hurricane season, wind shear in the Caribbean Sea and tropical Atlantic Ocean tends to be lower, and rising air can be enhanced, both factors favoring tropical storm and hurricane formation.

La Niña developed during the 2017 season and was solidly in place for the 2021 season. from meteorologist Eric Webb found a moderate La Niña was also in place for the 1933 season.

The increasing likelihood of a through fall is one factor behind forecasts of in 2022.

If we manage to generate "Bonnie" east of the Lesser Antilles, that could be another kernel of evidence supporting that outlook.

Now is a good time to well before a storm or hurricane threatens.

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