UPDATE 4-US forecaster lowers Atlantic hurricane prediction

* CSU predicts six hurricanes, two expected to be "major"

* Sea temperatures have cooled, weak El Nino could emerge

* 31 pct chance of "major" hurricane hitting US Gulf coast (Adds comment from National Hurricane Center director)

By Jim Loney

MIAMI, April 7 (Reuters) - Citing cooler seas and the prospect of a weak El Nino, Colorado State University's hurricane team lowered its 2009 Atlantic forecast on Tuesday to 12 tropical storms, of which six could become hurricanes.

The research team, founded by storm forecasting pioneer William Gray, said the season could see two "major" hurricanes of Category 3 or higher on the five-step Saffir-Simpson intensity scale. Hurricanes of that magnitude have sustained winds of more than 110 miles per hour (177 km per hour).

In its December forecast, the CSU team predicted 14 storms, seven hurricanes and three major hurricanes in the 2009 season, which begins on June 1 and lasts six months.

The researchers said sea surface temperatures in the tropical Atlantic Ocean had cooled in recent months. Hurricanes draw energy from warm sea water, so cooler water could diminish hurricane activity.

In addition, the eastern Pacific Ocean could see the current weak La Nina conditions change to neutral, or even weak El Nino, by June, the researchers said. El Nino is a warm water phenomenon that can suppress Atlantic hurricane formation.