Hurricane Melissa, now a Category 5 monster, began its northwest turn Monday evening, churning toward Jamaica with what will likely be the most powerful winds ever recorded on the Caribbean island.

British tourists in Jamaica have been told to prepare as the island’s strongest storm on record closes in.

When Melissa came ashore it tied strength records for Atlantic hurricanes making landfall, both in wind speed and barometric pressure, which is a key measurement that meteorologists use, said Klotzba...