Helene becomes season's fourth Atlantic hurricane

TALLAHASSEE, Fla, Sep 17 (Reuters) Helene became the fourth hurricane of the Atlantic season and Hurricane Gordon stalled in the Atlantic, but neither storm threatened land.

By 11 am. EDT (2030 hrs IST, Helene had reached hurricane status with sustained winds of 75 miles per hour (120 kph) as it trekked to the northwest about 1,145 miles (1,845 km) east of the Leeward Islands, the US National Hurricane Center said.

''A plateauing of the intensity is called for around 72 hours with slight weakening thereafter,'' the Miami-based hurricane center predicted.

Gordon, the third only hurricane of the 2006 season to become a ''major'' storm of Category 3 or higher on the five-step Saffir-Simpson scale, continued to pose no threat to land on Saturday.

Located 655 miles (1,055 km) east of Bermuda, Gordon had 100 mph (160 kph) winds -- making it a Category 2 hurricane -- and was expected to weaken as it moved northeastward.

The six-month Atlantic storm season that began on June 1 has been relatively calm compared to last year's 28 tropical storms, of which 15 became hurricanes.

Tropical storms Alberto and Ernesto struck the United States but caused no serious damage and one hurricane, Florence, grazed the British mid-Atlantic territory of Bermuda. Last year, Hurricane Katrina devastated New Orleans, killing 1,500 people on the US Gulf Coast.

Computer models show slim chances for Helene to reach the US East Coast as it was more likely to curve northwestward over the open Atlantic.

Hurricane forecasters had originally predicted that this Atlantic storm season would be busier than usual, as were both record-busting 2005 and the season of 2004, when four hurricanes in a row carved a destructive path through Florida.

But the development of El Nino weather conditions in the Pacific, and other factors such as high quantities of West African dust in the atmosphere over the Atlantic, have led weather experts to reduce their expectations.

The El Nino phenomenon, an unusual warming of waters in the eastern Pacific, causes high wind shear over the Atlantic. Wind shear, the difference in velocity or direction of winds at different altitudes, tears cyclones apart.

REUTERS AD PM0833