By Chris Spears

DENVER (CBS4) – Each year the end of November brings a sigh of relief to millions of Americans along the Gulf and Atlantic coasts because it marks the end of hurricane season.

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The Atlantic hurricane season runs from June 1 to Nov. 30.

A debris covered street caused when the Arecibo River overflowed is seen Saturday in the aftermath of Hurricane Maria, in Arecibo, Puerto Rico.
(credit: Ricardo Arduengo/AFP/Getty Images)

This year was extraordinarily active and under-predicted by the Colorado State University Tropical Meteorology Project forecast team.

“The 2017 hurricane season was extremely active. Overall, our predicted numbers from our early July and August issue dates for named storm and hurricane formations were relatively close to what was observed, but our early season predictions and our predictions for integrated metrics such as Accumulated Cyclone Energy (ACE) were far too low,” said Phil Klotzbach, lead author of the forecast.

The team says that several factors likely combined to make for such a memorable year, including an El Niño that was anticipated in the spring of 2017 but did not develop. They also say that the waters of the tropical Atlantic were much warmer than normal and that played a role.

A lake is hit by Hurricane Irma in Pembroke Pines, Florida on Sunday.
Hurricane Irma’s eyewall slammed into the lower Florida Keys, lashing the island chain with fearsome wind gusts, the US National Hurricane Center said. (credit: Michele Eve Sandberg/AFP/Getty Images)

In the first CSU forecast issued on April 6, the team called for 11 named storms, four hurricanes and two major hurricanes. They increased their forecast on June 1 and called for 14 named storms, six hurricanes and two major hurricanes.

Future updates continued to increase levels of activity predicted in 2017, calling for 15 named storms, eight hurricanes and three major hurricanes on July 5, and 16 named storms, eight hurricanes and three major hurricanes on Aug. 4.

Observed activity was 17 named storms, 10 hurricanes and six major hurricanes.

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Other hurricane statistics for 2017 include…

• September 2017 broke Atlantic calendar month records for named storm days (53.5), hurricane days (40.25), major hurricane days (18) and Accumulated Cyclone Energy (175)

• Harvey was the first Category 4 hurricane to make landfall in Texas since Carla (1961)

• Irma’s maximum intensity of 160 knots was the strongest winds recorded by an Atlantic hurricane outside of the Gulf of Mexico and Caribbean on record

• Harvey and Irma marked the first time that two Category 4 hurricanes have made continental United States landfall in the same year

• Maria was the first Category 4 hurricane to make landfall in Puerto Rico since 1932 and the strongest hurricane to make landfall in Puerto Rico since 1928

The Tropical Meteorology Project has been issuing forecasts for the past 34 years. A brief qualitative outlook for the 2018 hurricane season will be issued on Wednesday, Dec. 13, with a first full forecast issued in early April 2018.

You can read the full report released by CSU here.

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Meteorologist Chris Spears travels weekly in the CBS4 Mobile Weather Lab reporting about Colorado’s weather and climate. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.