UPDATE 1-Colorado State researchers reduce forecast for named tropical storms in 2021

(Adds details from forecast, latest NOAA forecast)

HOUSTON, Aug 5 (Reuters) - Researchers at Colorado State University on Thursday reduced their forecast for named tropical storms from 20 to 18 expected in the 2021 Atlantic hurricane season.

The closely watched forecast kept unchanged the number of hurricanes forecast for 2021 at nine and the number of major hurricanes at four in what is still expected to be an above-average season, according to the paper released online on Thursday.

Warmer sea surface temperatures and reduced wind shear point to an above-average season, according to the forecast, but models based on the previous 39 years point to a lower number of named storms.

The increase is in line with the outlook released on Wednesday by the U.S. National Oceanic and Atmospheric Administration (NOAA) that predicted 15-21 named storms for the season, which began on June 1 and continues to Nov. 30, with peak activity between August and October.

NOAA increased to 21 from 20 the upper limit of its prediction of named storms.

The forecast includes five named storms so far this year. Two systems in the eastern Atlantic have a chance to develop into tropical storms, the U.S. National Hurricane Center said on Thursday. There has not been a storm since Hurricane Elsa dissipated on July 9 over the eastern United States.

This year is forecast to be the sixth straight above-average U.S. Atlantic hurricane season. The record 2020 season had 30 named storms.

An average hurricane season in the Atlantic between 1991 and 2020 saw three major hurricanes, seven hurricanes and 14 tropical storms.

Major hurricanes have sustained winds of at least 111 miles per hour (178 kph). (Reporting by Erwin Sebad; editing by Jonathan Oatis and David Gregorio)