Jamaican residents and businesses prepare for Hurricane Dean to make landfall as a possible Category 5 storm reaching speeds of up to 150 mph (240 kilometres per hour). Hurricane Dean was on the verge of becoming a rare Category 5 storm on Saturday (August 18) as it took aim at Jamaica, Mexico's Yucatan Peninsula and the oil and gas-rich Gulf of Mexico after pounding the eastern Caribbean, where it was blamed for at least three deaths. Millions of people were under storm alerts in some of the most populous areas of the Caribbean, including parts of vulnerable Haiti and its teeming capital, Port-au-Prince, the Dominican Republic, Cuba, and all of mountainous Jamaica, which was in the direct path of the powerful hurricane. With sustained winds of 150 mph (240 kilometres per hour), Dean was a Category 4 storm, the second highest level on the five-step Saffir-Simpson scale of hurricane intensity. It was expected to become a Category 5 storm within two days, with sustained winds of more than 155 mph (250 kph). Jamaica's government urged people to flee low-lying and landslide-prone areas, buses were marshaled to transport evacuees and police and troops were put on alert. Political parties suspended campaigning for August 27 national elections. Lines formed at gas stations, and people crowded markets, emptying shelves of batteries, canned tuna, rice and bottled water. Dean's progress was being watched by energy markets, which have been roiled by hurricanes since powerful storms in 2004 and 2005 disrupted oil and gas production. Energy firms evacuated workers from offshore rigs in the Gulf of Mexico, home to a third of U.S. domestic crude production. The latest computer models showed Dean hitting the Yucatan around Tuesday before emerging in the Gulf of Mexico, where it could go through Cantarell Complex of Mexican oil fields, one of the world's most productive. Most had the storm hitting the Mexico coast after that but one took it ashore in southern Texas by Thursday. Category 5 hurricanes are rare. Until the record-breaking 2005 Atlantic hurricane season, records showed only two years -- 1960 and 1961 -- with more than one Category 5 storm. But in 2005, four hurricanes reached that strength -- Emily, Katrina, Rita and Wilma. Wilma became the most powerful hurricane ever observed in the Atlantic. Across the region, fishing boats were ordered into port, tourists scrambled to get out and residents got ready.