Final answer:
At 5 a.m. AST on Thursday, 31 August, Irma was categorized as a hurricane, a term defined as a storm (option b) with sustained winds of 74 mph or higher on the Saffir-Simpson Scale.
Step-by-step explanation:
At 5 a.m. AST on Thursday, 31 August, the category to describe Irma would be 'hurricane'. According to the Saffir-Simpson Scale, a hurricane is a storm with sustained winds of 74 miles per hour or higher. Hurricanes develop over warm waters, typically greater than 80 °F, and require certain atmospheric conditions such as a drop in atmospheric pressure to intensify from a tropical depression into a tropical storm and eventually into a hurricane. The cyclonic motion and the warm temperatures feed the system, further strengthening it, and the Earth's rotation contributes to the storm's rotation, counterclockwise in the Northern Hemisphere and clockwise if south of the equator.
Hurricane Irene in 2011, for example, intensified and was captured on a satellite image as it approached New York City. Hurricanes are known for causing torrential rainfall, high winds, and significant damage, emphasizing the importance of tracking and preparation for such severe weather events. The devastating impact of hurricanes like Katrina in 2005 illustrated the potential for not only meteorological but also socio-economic and infrastructural crises when such storms hit populated areas.