(Updates storm position, strength, details on separate weather system)

MIAMI, July 31 (Reuters) - Tropical Storm Chantal formed in the north Atlantic on Tuesday and its sustained winds grew to 50 mph (80 kph) but it posed no threat to the United States, forecasters said.

At 5 p.m. (2100 GMT), Chantal was about 235 miles (375 km) south-southeast of Halifax, Nova Scotia, and moving rapidly toward the northeast near 26 mph (42 kph), according to the U.S. National Hurricane Center in Miami.

Chantal, the third tropical storm of the year, was on a track that would take it near Canada's Newfoundland on Wednesday. It was not expected to intensify as it charged into cooler waters.

Of more interest to weather watchers was a tropical wave in the far Atlantic that also had the potential to become a depression and perhaps a storm in the coming days.

At 5:30 p.m. (2130 GMT), the low pressure area was about 485 miles (780 km) east of the southern Windward Islands and moving at 10 mph to 15 mph (16 kph to 24 kph) westward toward the Caribbean.

The system had the potential to head eventually for the Gulf of Mexico, the source of roughly a third of U.S. domestic oil and gas output.

A series of devastating hurricanes in 2004 and 2005, including Katrina, which swamped New Orleans, sent oil prices soaring when they ripped through U.S. oil and gas facilities.

The 2006 hurricane season was mild in comparison and no hurricanes hit the United States last year. Tropical storms become hurricanes when their top winds reach 74 mph (119 kph).

Forecasters have predicted another above-average storm season this year, with estimates ranging from 13 to 17 storms during the six-month season, which began on June 1.

Two named storms have already formed: Andrea, a subtropical storm, formed in May, and Barry on June 1. The height of the season statistically occurs on Sept. 10.

AlertNet news is provided by