WASHINGTON — (CNN) The first Atlantic hurricane of the year reached major status on Friday, strengthening to a Category 3 storm about 900 miles east of the eastern Caribbean islands, the National Hurricane Center said.

But forecasts call for a weakening trend as Hurricane Danny heads west, and CNN’s forecast track shows it could reach the Leeward Islands such as Guadeloupe and Montserrat as only a tropical storm around Monday morning.

Danny had estimated maximum sustained winds of 115 mph early Friday afternoon, the hurricane center said, citing measurements taken by a National Oceanic and Atmospheric Administration aircraft.

Yet the storm was moving into an “area of unfavorable upper-level winds” that are expected to help weaken it later Friday, the center said.

Danny is relatively tiny, forecasters say, with hurricane-force winds extending only 15 miles from its center on Friday morning.

The hurricane center cautioned that Danny’s small diameter makes forecasting its strength especially difficult.

“Danny’s compact size makes it subject to significant fluctuations in strength, both up and down, and such fluctuations are notoriously difficult to forecast,” the center said in a forecast discussion online on Thursday.

Danny on Tuesday became the first named storm of the Atlantic season — unusually, if not unexpectedly, late.

Forecasters had already said this year’s season would produce a below-normal number of Atlantic Ocean hurricanes, in part because of this year’s strong El Niño, which is causing strong wind shears in the Atlantic, hindering cyclone development.

Tropical Storm Kilo in Pacific could threaten Hawaii next week

Meanwhile, a depression in the Pacific strengthened into what is now called Tropical Storm Kilo on Friday, spinning about 535 miles south-southeast of Hilo, Hawaii.

Forecasters believe the storm could strengthen into a hurricane by Monday, the Central Pacific Hurricane Center said. A forecast track shows it could swing under Hawaii before turning back toward it, possibly threatening the state as a hurricane early Wednesday.

Kilo had maximum sustained winds of 40 mph on Friday morning, the center said. Tropical storms have maximum sustained winds speeds of at least 39 mph.

A different Pacific storm — a tropical depression — formed Thursday and could become a tropical storm Friday. It was about 850 miles south of Midway Island on Friday morning, and a forecast track indicates it could be near Midway as a tropical storm on Wednesday.

El Niño’s effect on Atlantic hurricanes

Hurricane Arthur, a Category 2 storm, was the last hurricane to make landfall in the United States when it came ashore in July 2014 between Cape Lookout and Beaufort on Emerald Island, North Carolina, the National Hurricane Center said.

It has been the longest period to pass without a major hurricane hitting the United States since reliable record keeping began in 1850, a 2015 NASA study said.

Though forecasters are calling for a below-average storm season in the Atlantic, Hennen said any hurricane that does emerge this year can have a strong impact.

Hurricane Andrew struck South Florida and south-central Louisiana in August 1992 with 175-mph winds, wiping out entire communities, killing 23 people and causing more than $25 billion in damage.

According to the National Oceanic and Atmospheric Administration Climate Prediction Center, which has updated its 2015 Atlantic hurricane season outlook, there is a 90% chance of a below-normal hurricane season and a lower chance of expected storm activity in the United States this year.

Of the six to 10 named storms for this season, one to four storms are likely to become hurricanes in 2015.

There’s an even smaller chance that one of these storms will transform into a major hurricane. The National Hurricane Center calls any Category 3 or higher storm a major hurricane.

Also, the Atlantic Ocean has had much cooler temperatures, which decreases the chances of major storm activity.

Since 1995, the United States has been in a high hurricane activity area, which typically lasts around 25 years. But for almost a decade, the country hasn’t seen a hurricane greater than a Category 3 storm, putting it in a nine-year hurricane “drought.”

The United States still has seen some big storms in the past few years. In 2012, hurricane-turned-cyclone Superstorm Sandy ravaged the Northeast with damaging flooding and powerful winds.

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