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Why the Tropical Atlantic Ocean Is Different from This Time Last Year, and What It Could Mean for Hurricane Season

At a Glance

Sea-surface temperatures in the tropical Atlantic Ocean have cooled below average.
This could play a role in the upcoming hurricane season.
Coastal residents should remain prepared no matter how active or inactive a hurricane season is predicted to be.

Water temperatures across the ocean's surface in the tropical Atlantic Ocean this spring could be offering a hint for what to expect this hurricane season.

Throughout the main development region (MDR) of the Atlantic Ocean, sea-surface temperatures (SSTs) at the start of May were running nearly a half-degree Celsius below the 1981-2010 average, according to a tweet from Dr. Phil Klotzbach, a tropical scientist at Colorado State University. The MDR is a swath of the tropical Atlantic Ocean that stretches from Africa's western coast into the Caribbean.

(MORE: Hurricane Central)

This is a change from last year at this time when warmer-than-average SSTs dominated much of the MDR, helping to fuel last year's active hurricane season.

Cooler-than-average sea-surface temperatures dominated the tropical Atlantic Ocean as of early May. Parts of the western and central Atlantic are warmer than average.

In addition, this swath of the ocean had its coolest final two weeks of April in 18 years, according to a tweet from Michael Lowry, a strategic planner with FEMA and former hurricane specialist at The Weather Channel.

Should the cooler waters persist into summer, it could suppress tropical storm or hurricane development in this region of the Atlantic Ocean.

This is because of the negative effect the cooler waters have on tropical waves as they move westward across the Atlantic Ocean from Africa. If you recall, tropical waves are one of the seeds for tropical storm and hurricane development.

"In terms of Atlantic SSTs and their impacts on tropical waves, anomalously cool water effectively means less fuel for developing tropical cyclones. It also tends to be associated with higher pressure and drier mid-levels in the atmosphere, which both act to suppress the development of strong thunderstorms which are the building blocks of hurricanes," said Klotzbach in an email to weather.com.

April's cool water temperatures were one of the factors weighed in the hurricane season outlook issued in late April by The Weather Company, an IBM Business.

Numbers of Atlantic Basin named storms (those that attain at least tropical storm strength), hurricanes and hurricanes of Category 3 or higher intensity forecast by The Weather Company and Colorado State University, compared to the 30-year average (1981-2010).

The Weather Company compared SST anomalies in April for inactive versus active hurricane seasons and found the current pattern more closely represents inactive hurricane seasons. Activity in the Atlantic this hurricane season was forecast by The Weather Company to be near the 1981-2010 average with 13 named storms, six of which are forecast to attain hurricane strength.

(MORE: 2018 Hurricane Season Outlook)

Of course, water temperatures in this region of the Atlantic are only one factor that determines how active or inactive a hurricane season will be. It's also possible that this patch of cool water in the tropical Atlantic gradually warms near or above average during the next few months.

Residents of the Caribbean and the coastal United States shouldn't let their guard down or cease preparations for the 2018 hurricane season even if the cooler water promotes a slower hurricane season overall.

It only takes one powerful hurricane landfall to make for a disastrous year, as Andrew in 1992 illustrated.

(MORE: Don't Let Your Guard Down, It Only Takes One)