Up to 25 named storms are expected this year as forecasters warned of an “extremely active” hurricane season.

The US National Oceanic and Atmospheric Administration increased its prediction by six after the season got off at a rapid pace over the past few weeks. A record-setting nine named storms have been logged so far, compared with the normal average of two.

Wilbur Ross, the US Secretary of Commerce, said in the Atlantic Hurricane Season Outlook: “This is one of the most active seasonal forecasts that Noaa has produced in its 22-year history of hurricane outlooks.

We encourage all Americans to do their part by getting prepared, remaining vigilant and being ready to take action when necessary.”

Mark Guishard, the director of the Bermuda Weather Service, said: “Residents should be prepared, as in every year, for hurricane activity affecting Bermuda.

“As recent years have shown, warming upper-ocean temperatures have more frequently supported stronger storms that approach Bermuda during the peak of the season.

“I urge the public to maintain vigilance during this very busy and potentially less predictable Atlantic hurricane season.

“As has been demonstrated time and time again, during both active and inactive years, it only takes one storm to make it an impactful season for us.”

Dr Guishard said that the Covid-19 pandemic had impacted forecasting globally but that Bermuda’s meteorologists had continued to provide forecasts and warnings, thanks to the Bermuda Airport Authority’s pandemic response protocols.

He added: “That less aviation is occurring than usual means that there are less atmospheric measurements being taken by aircraft instruments.

“These measurements would normally be fed into computer-based weather models that meteorologists use for forecasting.

“With the reduction of aircraft weather observations, the predictability of hurricanes may be impacted.

“Scientific studies have shown the high value of aircraft-based observations in weather forecasting.”

Tropical storms Arthur and Edouard have already come within 115 miles of Bermuda this season, but neither caused significant impact locally.

An average season produces 12 named storms, including six hurricanes, with three of them Category 3 or stronger.

Noaa’s Climate Prediction Centre predicted in May that there would be between 13 and 19 named storms and that six to ten of them could become hurricanes, including three to six major hurricanes with sustained winds of at least 111mph.

The updated outlook predicts 19 to 25 named storms, of which seven to 11 will become hurricanes, including three to six major hurricanes.

The chance of an above-normal hurricane season has increased from 60 per cent to 85 per cent.

Gerry Bell, lead seasonal hurricane forecaster at the Climate Prediction Centre, said: “We expect more, stronger and longer-lived storms than average, and our predicted Accumulated Cyclone Energy range extends well above Noaa’s threshold for an extremely active season.”

Noaa highlighted warmer-than-average sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea, reduced vertical wind shear, weaker tropical Atlantic trade winds and an enhanced West African monsoon.

The conditions are expected to continue for several months because of a warm phase of the Atlantic Multi-Decadal Oscillation, which reappeared in 1995 and has been responsible for more active hurricane seasons.

La Niña — a cooling of the water in the equatorial Pacific, which occurs at irregular intervals, and is associated with widespread changes in weather patterns — could also develop in the months ahead and weaken the wind shear over the Atlantic Basin, which would allow storms to develop and intensify.

A total of 18 named storms formed in the Atlantic last year, including six hurricanes, three of them major.

The only hurricane that affected Bermuda was Humberto, a Category 3 storm, which damaged hundreds of roofs, downed trees and knocked out power across the island as it passed to the north of the island in September.