Hurricane Lorenzo has slipped back to Category 4 force in the central Atlantic Ocean after several hours as a Category 5 — which made it the strongest storm observed so far north and east in the Atlantic basin.

The US National Hurricane Centre said the storm had maximum sustained winds of 155mph.

Lorenzo is moving north at 10mph and is centred more than 1,000 miles south west of the Azores, a Portuguese island chain.

There are no coastal watches or warnings in effect, although forecasters expect the storm to remain strong as it approaches the Azores over the next few days, and it might eventually reach Ireland or the UK at tropical storm force.

Officials said swells produced by the storm were affecting parts of the north-eastern coast of South America and the Lesser Antilles.

Meanwhile, Tropical Storm Narda has started pounded the Mexican coast near the resort of Zihuatanejo, bringing heavy rain and a threat of flooding.

The US National Hurricane Centre said the storm had maximum sustained winds of 45mph, and the forecast track would keep it right along Mexico’s Pacific coast in the coming days.

The biggest threat appears to be rain. The Hurricane Centre said Narda is expected to produce 5in to 10in of rain along the coast from Oaxaca to Nayarit — a stretch that includes Acapulco and Puerto Vallarta.