The news of Tropical Storm Rita has renewed market jitters - crude oil futures surged more than US$4 yesterday, the biggest one-day hike on record.

Tropical Storm Rita, with wind speeds of over 110km per hour, is expected to intensify into a hurricane today, according to an advisory issued by the hurricane centre at 8pm in New York yesterday (10am AEST this morning).

Long-range forecasts show the storm moving into the Gulf later this week as a hurricane, before possibly approaching Mexico or Texas.

Chevron and Shell started evacuating workers from offshore oil and gas platforms and rigs in the Gulf yesterday.

About 55% of oil production and 35% of gas production in the Gulf remains halted in the wake of Hurricane Katrina, said the US Minerals Management Service.

The new hurricane research from the Georgia Institute of Technology, Atlanta, said the actual number of hurricanes reported around the world each year had barely changed, but the number of category four and five cyclones, such as Katrina, had doubled since the 1970s.

The biggest jump in intense storms occurred in the north Pacific, south-west Pacific and the northern and southern Indian oceans, said the report.

Global warming could account for this trend, said the researchers. Hurricanes are powered by warm ocean water and there had been a worldwide 0.5C increase in sea surface temperatures in the last 30 or so years.

“In the 1970s, there was an average of about 10 category four and five hurricanes per year globally,” said the centre’s atmospheric scientist and team leader Peter Webster.

“Since 1990, the number of category four and five hurricanes has almost doubled, averaging 18 per year globally.”

This is bad news for the oil and gas industry, which is now considering revising its storm standards for platform criteria.

Around the world, offshore platforms are generally built to survive a so-called 100-year storm – a hurricane so strong that it only typically occurs once every 100 years.

But Hurricane Ivan, which smashed Gulf of Mexico infrastructure a year ago, and Katrina, which tore through less than one month ago, support the theory that more intense storms are still to come.

“Most definitions of a 100-year event were calculated before Ivan and Katrina,” said spokesperson from ocean-engineering enterprise Woods Hole Group.

“At this point, are the 100-year criteria good enough?”

Late yesterday, the US government approved the seventh loan request for crude oil from their reserves.