Near-Average 2018 Atlantic Hurricane Season Expected, According to The Weather Company's Updated May Outlook

(MORE: Hurricane Central)

The Weather Company expects 12 named storms during the season, including five hurricanes and two major hurricanes of Category 3 or higher intensity.

This is slightly less activity compared to the April outlook, which called for 13 named storms and six hurricanes this hurricane season.

The updated forecast is near the Atlantic Basin's 30-year historical average (1981-2010) of 12 named storms, six hurricanes and three major hurricanes and slightly less than the Colorado State University outlook released earlier this month.

There are several reasons forecasters are calling for these near-average numbers in 2018:

1. Atlantic Ocean Temperature Patterns

A pattern of cooler-than-average water temperatures has developed in the eastern Atlantic and in the central northern Atlantic.

The Weather Company compared sea-surface temperature anomalies in April for inactive vs. active hurricane seasons and found that the current pattern more closely represents inactive hurricane seasons.

Temperatures in the space between the Lesser Antilles and Africa are supportive for tropical growth nearly year-round, but the warmer the water in that region, the more likely a tropical cyclone is to develop, all other factors (wind shear, atmospheric moisture, forward speed, etc.) held constant.

Should this pattern of cooler-than-average ocean temperatures continue into the heart of hurricane season (August, September and October), we can expect less tropical activity west of Africa.

The Gulf of Mexico has warmed to near or even slightly above average since the last update in April.

(MORE: Water, Not Wind, the Deadliest Factor in U.S. Hurricanes and Tropical Storms)

2. Transition Toward El Niño?

Waters in the eastern equatorial Pacific Ocean have warmed to near-average, a sign of neutral conditions. Neither La Niña nor El Niño conditions are present as of mid-May.

The latest outlook from the Climate Prediction Center, released May 10, forecasts neutral conditions to last through the end of hurricane season before El Niño conditions potentially take over this winter. As we have seen so far in 2018, a gentle warming of the equatorial Pacific is anticipated through the end of the year.

The atmospheric component of this global atmospheric and oceanic phenomena is, so far, following right along with the oceanic portion of El Niño, according to The Weather Company's outlook.

The average tropical activity of these similar years was a near-average hurricane season.

How quickly waters warm in the equatorial Pacific Ocean is still a big question going into the upcoming hurricane season. A faster warming of the Pacific, or a quicker transition toward El Niño, could mean fewer storms and hurricanes, especially toward the end of hurricane season.

(MORE: April 2018 Was Earth's 400th Consecutive Warmer-Than-Average Month)

3. Increasing North Atlantic Oscillation

The North Atlantic Oscillation (NAO), defined as a pattern of pressure gradients over the northern Atlantic Ocean, is expected to remain positive through the rest of the spring.

Both the Azores-Bermuda high-pressure system and the Greenland low-pressure system are strengthened in the positive phase of the NAO. This creates a stronger pressure gradient and increased wind between the two systems. This also creates more wind around the Azores-Bermuda high.

• Gustier winds across much of the subtropics and North Atlantic.
• Cooler water temperatures.
• A slightly faster tropical wave track across the Atlantic.

The positive phase of the NAO decreases the chances of an active year.

(MORE: Explaining the Cone of Uncertainty)

4. The Multi-Decade Long Upward Swing in the Tropics Might Be Over

The tropics have long-period upward and downward swings in activity called the Atlantic Multidecadal Oscillation (AMO).

The current period of increased activity began in 1995 and has been responsible for monster seasons like 2004, 2005 and 2010. Prior to that, from 1965 through 1994, far fewer Atlantic hurricanes were produced each year.

The periods of increased and decreased activity last 20 to 40 years each and are a result of changes in the system of oceanic currents in the northern Atlantic Ocean.

The AMO is the climate background that all other climate and weather patterns build on in the Atlantic, including El Niño.

If we are beginning to see the end of the active phase of the AMO, the number of hurricanes will be generally near or below average for the next two or more decades.

Years in a low-activity AMO period with a strong El Niño are usually far-below-average seasons. Two such seasons are 1982 and 1987, which both had fewer than seven named storms.

(MORE: Where and When the Season's First Hurricane Typically Forms)

Other Hurricane Season Forecasts

Other seasonal forecasts for named storms (NS), hurricanes (HU) and major hurricanes (MH) include:

• Colorado State University: 14 NS, 7 HU, 3 MH
• North Carolina State University: 14-18 NS, 7-11 HU, 3-5 MH
• Tropical Storm Risk/University College London: 12 TS, 6 HU, 2 MH

What Does This Mean For the United States?

There is no strong correlation between the number of storms or hurricanes and U.S. landfalls in any given season. Residents near the coast should prepare each year, no matter what seasonal outlooks say.

A couple of classic examples that show the need to prepare each year occurred in 1992 and 1983.

The 1992 hurricane season produced only six named storms and one subtropical storm. However, one of those named storms was Hurricane Andrew, which devastated South Florida as a Category 5 hurricane.

In 1983, there were only four named storms, but one was Hurricane Alicia. The Category 3 hurricane hit the Houston-Galveston area and caused almost as many direct fatalities along the Texas coast as Andrew did in South Florida.

(MORE: Sudden-Developing Storms/Hurricanes Near the U.S.)

In contrast, the 2010 hurricane season was active. There were 19 named storms and 12 hurricanes that formed in the Atlantic Basin. Despite the high number of storms that year, no hurricanes and only one tropical storm made landfall in the U.S.

In other words, a season can deliver many storms but have little impact, or deliver few storms with one or more causing major impacts to the U.S. coast.

The U.S. averages one to two hurricane landfalls each season, according to NOAA's Hurricane Research Division.

It's impossible to know for certain if a U.S. hurricane strike, or multiple strikes, will occur this season. Keep in mind, however, that even a weak tropical storm hitting the U.S. can cause major impacts, particularly if it moves slowly and triggers flooding rainfall.

Hurricane season runs from June 1 through Nov. 30 in the Atlantic Basin.