Hurricane Gustav strengthened into a Category Three storm as it moved across warm Caribbean waters toward western Cuba. According to the US National Hurricane Centre Gustav's top winds had reached near 100 mph (155 kph) as it passed about 50 miles (85 km) northeast of Grand Cayman Island. The storm, which killed up to 77 people in the Caribbean, was plowing toward superheated waters south of Cuba where it could absorb enough energy to strengthen into a major hurricane before ripping through the heavy concentration of US oil and natural gas platforms off Louisiana. While long-range storm forecasts are prone to errors, the US National Hurricane Centre said on Friday night that Gustav could be a "major" Category 4 storm on the five-stage Saffir-Simpson scale of hurricane intensity within 48 hours. The storm's most likely track has it going ashore west of New Orleans on Tuesday morning. US emergency officials, mindful of the devastation caused by Hurricane Katrina three years ago, warned that Gustav was expected to be accompanied by a 15- to 30-ft (5-to-9m) storm surge along the Gulf Coast, and said four states in its potential path were expected to begin large-scale evacuations on Saturday. "This storm has the potential for being a very dangerous storm," said Bill Irwin, a program director with the US Army Corps of Engineers.