Why such an active hurricane season?

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(3TV/CBS 5) -

This week, Hurricane Irma became one of the strongest Atlantic hurricanes on record.  With sustained winds of 185 miles per hour, it became a Category 5 storm early Tuesday and was forecast to maintain that intensity through Friday. 

[SLIDESHOW: U.S. braces for Hurricane Irma]

[RELATED: Arizona task force on the road to provide help after Irma]

[WOW: A Delta commercial flight just raced Hurricane Irma to Puerto Rico]

This comes on the heels of another historic storm, Harvey, which left behind record-breaking rain and flooding in Houston.  And as of this writing on Wednesday, we’re also tracking Tropical Storm Katia in the Gulf of Mexico and Tropical Storm Jose in the Atlantic just behind Irma.  Jose is forecast to intensify to a hurricane in the next few days.

[READ: Hurricanes: Storms like no other]

It's been a very active Atlantic hurricane season so far, with our first named storm, Arlene, developing before the start of hurricane season in mid-April.  Hurricane season runs from June 1 through the end of November. September is the peak of the season and typically most active. 

[RELATED: 2017 Atlantic Hurricane Season off to early start]

NOAA issued their official forecast for the 2017 Atlantic hurricane season in May and updated it in early August. Both times, they forecast an above-normal, or more active than usual season. Above-normal seasons have higher numbers of named storms, hurricanes and major hurricanes (category 3 and higher) and longer-lasting storms. 

The August outlook forecast 14 to 19 named storms and two to five major hurricanes.

MOBILE/APP USERS:  Click here to see the Saffir-Simpson scale

They cite several reasons for calling for such an active season, including warmer sea surface temperatures this year and weaker trade winds, along with weaker wind shear. Essentially, that means warmer water to help fuel hurricane growth and no strong winds to tear the storms apart. 

[RELATED: Hurricane warning: Find out how a name affects your travel insurance]

El Niño conditions can sometimes lower Atlantic hurricane activity, but the latest outlook shows the chances of an El Niño forming have dropped, and we may be heading toward La Niña conditions instead.  That means sea surface temperatures in the central-eastern Pacific are cooling, part of a weather pattern that can influence weather conditions across the globe.  In this case, if La Niña conditions develop early enough, it could mean a more active end to hurricane season. 

[QUICK LESSON: El Niño and La Niña explained]

[READ MORE: El Niño and La Niña's effects on hurricane season]

We’ll have to wait and see if this rivals the 2005 season, the most active Atlantic hurricane season in recorded history.  That season brought a record seven major hurricanes, including four category five storms. Katrina and Wilma were among those. It’s the only time the Greek alphabet was used for naming storms after the list of names was used up.  Six Greek letter names had to be used. The final storm that season, Zeta, formed on Dec. 30, a full month after the end of hurricane season. 

[WATCH: Mike Watkiss recalls Hurricane Katrina 12 years ago]

[READ: Top 3 deadliest hurricanes in the U.S.]

[MORE: Weather blog]

MOBILE/APP USERS:  Click here to see NOAA's image of the 2017 Atlantic hurricane season names

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