How does the Atlantic hurricane season compare to the Pacific?

The 2017 Atlantic hurricane season is the most active the Atlantic has seen since 2005 according to Gerry Bell, lead seasonal hurricane forecaster for the National Oceanic and Atmospheric Administration, which means that through this point it has been almost as active as the average season currently being experienced in the eastern Pacific.

“The threshold for an above normal season for the Atlantic is a little bit lower than for the eastern Pacific,” said Bell.

Unlike the Atlantic hurricane season, which concentrates on the entire northern Atlantic, the Pacific is so large that it is divided into regions.

There have been 13 named storms in the Atlantic this year, eight of which have been hurricanes, with four of those being major hurricanes. Meanwhile, the 2017 eastern Pacific hurricane season has seen 14 named storms, eight hurricanes, and four major hurricanes, which lines up almost perfectly with the numbers of an average season.

How long does each season last?

Hurricane Fernanda spins through the Pacific on July 14

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Source: National Oceanic and Atmospheric Administration

The eastern Pacific hurricane season begins on May 15, which give it a head start on the June 1 start of the season in the Atlantic. Theoretically that gives the eastern Pacific more time to generate storms, but this year the Atlantic hurricane season’s first storm, Tropical Storm Arlene, spun up on April 19, almost a month and a half before the official start of the season.

The Pacific saw Tropical Storm Adrian on May 9, which, while nearly three weeks later than Arlene, still set a record as the earliest forming named storm in the eastern Pacific during the satellite era.

The eye of Hurricane Irma at Category 5 strength

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Source: NASA

The eastern Pacific’s season also reaches its peak in July, August and September, getting a one month jump on the Atlantic’s peak. Both seasons officially end on Nov. 30.

Which season is more intense?

More storms and stronger storms are produced in the eastern Pacific on average than during the average Atlantic season, which normally sees 12 named storms, six hurricanes and three major hurricanes according to National Hurricane Center spokesman Dennis Feltgen. Since 1995, though, the Atlantic hurricane season has tended to be stronger than normal according to Bell, and when that happens, it has an effect on the eastern Pacific season.

“Many of the Atlantic seasons since 1995 have been stronger than the Pacific. Now, prior to that, in the 70s, 80s and early 90s the Atlantic was quite suppressed while the Pacific was very strong,” said Bell. “There’s a seesaw type of effect.”

El Nino and La Nina are major factors in how each season shapes up according to Bell. A strong El Nino leads often times to a weaker Atlantic season and a stronger season in the eastern Pacific, whereas a strong La Nina has the opposite effect.

According to the National Weather Service, there is a 55 to 60 percent chance of a strong La Nina this winter, but it is too early to tell what influence it might have over the later parts of the Atlantic hurricane season if it happens.

Which season causes more damage?

Another thing to consider with hurricanes is their potential impact. While the eastern Pacific might see more and larger storms, they tend to do less harm than storms in the Atlantic. This is because tropical cyclones generally move from east to west. Cyclones moving west in the eastern Pacific tend to encounter only open ocean. Cyclones moving west in the Atlantic have the Caribbean, the Gulf Coast and the eastern seaboard of the U.S. directly in their sights.

“If eastern Pacific storms move far enough to the west they can certainly impact Hawaii,” said Bell. “In the last few years, but not this year, there were several threats to Hawaii. If you look at the long term average, three to four of these storms in the eastern Pacific will tend to curve up and make landfall along Mexico or down more toward Central America, but the general track of most of them is over the open ocean where they never really impact anybody.”

An eastern Pacific tropical storm has never hit the west coast of the continental U.S. according to Bell. On the other side of the country, though, roughly 80 million people live on the Gulf Coast and eastern seaboard, Bell said, and each of them is under threat during every Atlantic hurricane season.

“That’s why the Atlantic is such a huge basin of concern for us,” said Bell. “There’s a tremendous amount of people and property in the path of Atlantic hurricanes versus Pacific ones, but that is not to say that Pacific hurricanes don’t cause damage. Overall, though, many more people are in harm’s way from Atlantic storms.”

This story was originally published September 24, 2017 at 11:16 AM with the headline "How does the Atlantic hurricane season compare to the Pacific?."