Caribbean islands added to tropical storm watch as new formation grows in Atlantic

Several Caribbean islands were added to a tropical storm watch on Monday as a new major disturbance was brewing in an already turbulent Atlantic hurricane season.

Expected to be named Tropical Storm Ernesto later in the day, the most recent addition to what is predicted to be an “above normal” tropical storm season – fueled by “near-record warm ocean temperatures in Atlantic”, according to the National Oceanic and Atmospheric Administration (NOAA) – comes days after Hurricane Debby became the fourth named storm of the year.

The countries added to the watch list included Antigua, Barbuda, Saba and St Eustatius, Guadeloupe and St Maarten.

In an update last week, the NOAA said it still anticipates that the Atlantic region will produce 17-14 named storms this year, including eight to 13 hurricanes and four to seven major hurricanes.

An average hurricane season in the Atlantic has 14 named storms, seven hurricanes and three major hurricanes.

Four have already been named: Alberto and Chris, both tropical storms in the Gulf of Mexico; Beryl, the earliest category 5 hurricane on record in the Atlantic; and Debby, a category 1 hurricane that hit Florida’s Big Bend last week before stalling over South Carolina as a drenching tropical storm.

Debby killed at least eight people, including four in Florida, while leaving those in its path to cope with widespread power outages, flooding and road closures.

The latest storm formation, currently listed as Potential Tropical Cyclone Five, is not currently predicted to hit the US mainland. Puerto Rico and the US and British Virgin islands were already under a tropical storm watch when the other islands were added to the list.

The future Ernesto, the fifth named storm in the series, is likely to bring heavy rain, flash flooding and other stormy conditions to the islands it affects. But first the system must form into a tropical depression as it moves west across out of the Atlantic and into the Caribbean.

According to a National Hurricane Center update issued at 5am on Monday, the storm is 645 miles east-south-east of Antigua and heading west-north-west at 25 mph. Puerto Rico, the center said, can expect 3ft storm surges and around 10in of rain. It is not yet determined if the front will reach hurricane status.

As hurricane season enters its peak August to September period, climate scientists have said that warm ocean temperatures and the development of La Niña creating warmer water in the Pacific are contributing to storm formation.

Related: Storm Debby spirals to US north-east with forecasts of tornadoes and floods

According to the Colorado State University seasonal hurricane forecasting model , “extremely warm sea surface temperatures provide a much more conducive dynamic and thermodynamic environment for hurricane formation and intensification”.

After NOAA issued its prediction, Astrid Caldas, a senior climate scientist for community resilience with the Union of Concerned Scientists, said the summer season in the northern hemisphere “has increasingly become a time of dread for the dangers that await”.

“The people and places that have found themselves in the path of a tropical storm can attest to its utter and enduring devastation, which often hits communities of color and low-income communities the hardest,” Caldas said.

Caldas said it was “imperative” that policymakers and emergency planners “help keep communities safe by prioritizing investments to get homes, businesses and infrastructure in frontline communities climate-ready”.