Tropical Storm Alex was set to strengthen into a hurricane on Tuesday, delaying BP Plc's efforts to increase siphoning capacity at the gushing oil well in the Gulf of Mexico where some companies evacuated workers.

Alex was forecast to move slowly away from the Yucatan Peninsula over southern Gulf waters and curl northwest away from major oil-extraction facilities to make a second landfall in northern Mexico mid-week.

It is not expected to hurt oil capture systems at the BP oil spill or the company's plans to drill a pair of relief wells intended to plug the leak by August, a BP executive told reporters in Houston.

But waves as high as 12 feet (4 metres) would delay this week's plans to hook up a third system to capture much more oil, said Kent Wells, BP executive vice president.

As a precautionary measure, Shell Oil Co, Exxon Mobil Corp, Anadarko Petroleum Corp and Apache Corp evacuated nonessential workers from platforms near Alex's path. Shell also shut subsea production at the Auger and Brutus platforms over the weekend.

Traders and brokers kept a close eye on Alex, but oil prices fell toward $78 per barrel on Monday as most forecasters predicted the storm would pass southwest of major U.S. offshore oil and gas installations in the Gulf of Mexico.

A hurricane watch has been issued for the coast of Texas south of Baffin Bay to La Cruz in Mexico.

The ports of Dos Bocas and Cayo Arcas, which handle 80 per cent of Mexico's oil export shipping in the Gulf, have been closed since Sunday due to strong surf in the area.

State-run oil giant Pemex said its platforms in the Campeche Sound continued to work normally on Monday although it suspended helicopter flights to and from the facilities.

Pemex said it is monitoring wind and surf conditions caused by Alex. Its Isla del Carmen port, not essential for oil shipments, has been closed since Sunday night.

Barbara Blakely, a spokeswoman for Shell, told Reuters the company was closely monitoring Alex's advance in the Gulf but that its LNG plant in Altamira, Mexico was working as usual.

Deaths in Central America

The storm is due to make landfall again between Brownsville, Texas, and Ciudad Madero in Mexico at mid-week, mostly sparing BP oil collection efforts south of Louisiana.

Alex, the first named storm of the 2010 Atlantic hurricane season, gained some strength late Monday with sustained winds of about 65 mph (100 kmph) with higher gusts and was located about 45 miles (135 km) west-northwest of Campeche, Mexico. The system was nearly stationary through the afternoon but was moving north at 5 mph (7 kmph) through Monday night, the U.S. National Hurricane Center said.

"Additional strengthening is forecast... and Alex is expected to become a hurricane on Tuesday," the center said on its latest update.

At least 10 people have been killed in Central America since the weekend in accidents related to Alex, local authorities reported.

Three people died in El Salvador from flooding, two others were killed in a landslide in Guatemala and five people were swept away by swelling rivers in Nicaragua, emergency officials told Reuters.

Alex was expected to bring 3 to 6 inches (7 to 15 cm) of rain to the Yucatan Peninsula, southern Mexico and parts of Guatemala through Tuesday. Isolated torrents of up to 10 inches (23 cm) were possible over mountainous areas. Forecasters warned the rain could cause flash floods and mudslides.

The Atlantic hurricane season runs from June 1 to Nov 30 and meteorologists predict this year will be a very active one.

Hurricanes feed on warm water and the sea surface temperatures in the tropical Atlantic are higher than usual this year. – Reuters