Fewer Atlantic Hurricanes Expected This Season, According to Latest Colorado State Outlook. Here's Why.

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Including Subtropical Storm Alberto, Hurricane Beryl and Hurricane Chris, 12 named storms, five hurricanes and only one major hurricane of Category 3 or higher intensity are expected this season.

This is a slight increase from the July outlook in terms of named storms and hurricanes with both categories increased by one. This is in part due to the above-average tropical activity so far this year.

The average number of named storms is 12, based on 1981-2010 data, and the latest outlook calls for an average number of named storms. However, the average number of hurricanes is 6 with an average of 3 major hurricanes, which translates to fewer hurricanes, especially major hurricanes, than average. 

Even with below-average tropical activity expected, it is important to be prepared as it takes only one landfall to cause damage and injuries.

Three Factors At Play

Wind shear is one of the conditions that plays an important role in tropical cyclone formation. Recently, wind shear has been above-average in the Caribbean Sea.

Dr. Phil Klotzbach, tropical scientist and head of the CSU tropical forecast team, notes that vertical wind shear in July has been much stronger than average over the Caribbean. This typically correlates with a less active Atlantic hurricane season.

Based on data since 1979, July saw the fifth highest wind shear in the Caribbean, according to Michael Lowry, FEMA atmospheric scientist.

Wind shear in the Atlantic tends to be stronger than average in years when El Niño conditions are present.

In addition, the tropical Atlantic has also been drier than average in July. This has been the case over the past several Julys, but this year the dry conditions have been stronger and more persistent. Drier conditions in the tropical Atlantic in July are not favorable for hurricane formation.

The atmosphere has also been more stable. This means less thunderstorm development, which limits tropical cyclone development.

Water temperatures in the tropical Atlantic remain cooler than average. Water temperatures here are the coldest on record for Aug. 1 based on the average over the past 10 days, according to data since late 1981.

Klotzbach said water temperatures in the Atlantic in July do not resemble those typically observed in July during an active Atlantic hurricane season.

Potentially Similar Years

CSU scientists searched the historical record (since 1950) for years that had similar ocean and atmospheric conditions and trends to 2018.

In particular, they looked for years that had ENSO-neutral to weak El Niño conditions and cooler-than-average water temperatures in the main development region, the strip of water from western Africa into the Caribbean Sea.

The five hurricane seasons that had closest conditions to this year were 1968, 1986, 1993, 1994 and 2002. Compared to these years, 2018 is anticipated to have slightly greater activity, mainly due to the season's active start.

However, during those previous years, there were multiple impacts from tropical systems.

For example, in 2002, which was slightly below average in tropical cyclone activity, the U.S. was impacted by several systems: Tropical Storm Bertha, Tropical Storm Edouard, Tropical Storm Fay, Tropical Storm Hanna, Hurricane Isidore, Hurricane Kyle and Hurricane Lili.

Hurricane Isidore and Hurricane Lili both were both major hurricanes at one point but weakened before making landfall in the U.S. Both storms also made landfall in Louisiana within a week of each other and caused more than a billion dollars in damage and several deaths.