MIAMI (Reuters)—U.S. government scientists Thursday reduced their forecast for the 2010 Atlantic-Caribbean hurricane season but said they were still predicting a very active year of eight to 12 hurricanes.

The National Oceanic and Atmospheric Administration said it now expects 14 to 20 tropical storms, with eight to 12 of those strengthening into hurricanes.

It forecast that four to six of them would become “major” hurricanes, which are ranked at Category 3 or above on the five-step Saffir-Simpson scale of intensity and have top winds of more than 110 mph.

Before the six-month season began on June 1, NOAA had forecast 14 to 23 tropical storms, with eight to 14 developing into hurricanes, and three to seven becoming major hurricanes.

The revision reflected the lower-than-expected number of storms that developed in June and July.

"We're still predicting a very active hurricane season, and it's very important that people understand that," said Gerry Bell, the lead hurricane seasonal forecaster with NOAA's Climate Prediction Center.

The 2010 season has seen three tropical storms so far, with only one reaching hurricane strength.

The season is just nearing its traditionally most active phase, which runs from mid-August through October. Hurricanes feed on warm water, and the tropical Atlantic is warmest during that time.

The weather pattern known as La Nina also formed rapidly in July, bringing wind conditions that foster Atlantic hurricane formation, Mr. Bell said.

"I'm not sure I'd say (it's) unusually strong," he said. "This is not a record type of event by any means but it's a La Nina that's already having impact."

La Nina is a cooling of the sea surface in the tropical Pacific and has broad impact on global weather. It reduces the shearing winds that can disrupt nascent storms in the Atlantic.

The Atlantic is already in the midst of an active hurricane period that began in 1995 and could last another decade or two.

When La Nina forms during such a period, "that sets up just a perfect environment for these systems to form and strengthen,” Mr.Bell said.

In its preseason forecast, NOAA had said the 2010 season could rival the record-busting 2005 season that brought 28 storms, including Hurricane Katrina.

That seems less likely now, but still "everything is in place for a very active year," Mr. Bell said.