2018 Atlantic Hurricane Season Now Expected to Be Less Active, According to Colorado State University's Updated July Outlook

Including May's Subtropical Storm Alberto, 11 named storms, four hurricanes and only one major hurricane of Category 3 or higher intensity are expected this season in CSU's latest outlook released Monday. 

This is a significant reduction from its May 31 outlook, which had called for 14 total named storms, six hurricanes and two major hurricanes, and nearly matches the outlook released in late June by The Weather Company, an IBM Business.

There are several reasons these outlooks are calling for lower numbers in 2018:

1. Atlantic Ocean Temperature Patterns

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

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

Temperatures 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 east of the Caribbean.

The Gulf of Mexico, while supportive of tropical storms and hurricanes, has cooled relative to average since May. Subtropical Storm Alberto was able to develop over these waters in late May.

2. Transition Toward El Niño Becoming More Possible

Waters in the central and eastern equatorial Pacific Ocean have warmed above average but are still short of El Niño conditions as of early July.

The latest outlook from NOAA's Climate Prediction Center, released June 14, forecasts neutral conditions to last through much of the summer, if not into the autumn, before El Niño conditions potentially take over later this fall. This is a few months earlier than forecast in earlier outlooks.

The atmospheric component of this global atmospheric and oceanic phenomena is, so far, also leaning toward a less active season than originally thought. Dr. Michael Ventrice, The Weather Company meteorological scientist, noted model guidance suggesting the atmosphere's response to this warming water may finally be shifting toward what you'd expect from an El Niño.

FEMA atmospheric scientist Michael Lowry also noted wind shear over the Caribbean Sea was abnormally strong in June, taking on the overall look of a hurricane season feeling the effects of a developing El Niño.

Dr. Phil Klotzbach, tropical scientist and head of the CSU tropical forecast team, emphasized in the CSU July outlook that while a weak El Niño may develop, the main reason the team adjusted its late-May forecast down was the cooler tropical Atlantic water, rather than the equatorial Pacific warming.

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.

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 next few months.

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.

In the winter, this means a quicker storm track for winter storms crossing the northern Atlantic, but in hurricane season, it may bring a few less-than-favorable conditions:

• 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: 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:

• North Carolina State University (issued in April): 14-18 NS, 7-11 HU, 3-5 MH
• Tropical Storm Risk/University College London (issued in April): 9 TS, 4 HU, 1 MH
• NOAA (issued in late May): 10-16 NS, 5-9 HU, 1-4 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.

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.