(Updates with details on Tropical Storm Chris, flood threat in Puerto Rico)
By Maria Caspani and Rich McKay
July 9 (Reuters) - Tropical Storm Chris strengthened in the mid-Atlantic and was expected to become a hurricane on Monday evening or Tuesday, while the former Hurricane Beryl dwindled into a heavy rainstorm threatening to bring flooding to Puerto Rico, forecasters said.
Chris, which formed off the North Carolina coast early on Sunday, was packing maximum sustained winds near 70 miles per hour (110 kph) on Monday afternoon, causing swells that will batter the coasts of the Carolinas for the next few days, the National Hurricane Center said.
"These swells could cause life-threatening surf and rip current conditions," it said.
As of 5 p.m. EDT (2100 GMT), the storm was about 215 miles (350 km) south-southeast of Cape Hatteras, North Carolina. A tropical storm becomes a hurricane when its top sustained winds reach 74 mph (120 kph).
Chris will begin a northeastern course from late Tuesday off the U.S. Atlantic coast, the center said, adding that projections showed it possibly making landfall in the Canadian province of Nova Scotia late on Wednesday or early on Thursday.
The remnants of Beryl looked set on Monday to bring 2 to 4 inches (5-10 cm) of rain to Puerto Rico, which is still trying to recover from hurricanes that walloped the U.S. territory a year ago, causing an estimated $90 billion in damage.
The National Weather Service issued a flash-flood watch for Puerto Rico, warning of thunderstorms and wind gusts.
It also issued a flash-flood watch for the U.S. Virgin Islands through Monday evening. Tropical storm watches were in effect for Dominica and Guadeloupe.
Puerto Rico Governor Ricardo Rossello said the territory had opened more than 40 evacuation shelters for those in need.
Hurricane Maria dealt a vicious blow when it hit Puerto Rico on Sept. 20 with winds close to 150 mph (240 kph), knocking out the island's already teetering electric grid and water supply.
A study released in May estimated the death toll from Maria was about 4,645 - not the 64 long pegged by the island's government as the official death toll - which would make it one of the deadliest natural disasters in U.S. history.
About 7,000 houses and businesses in Puerto Rico still lack power after Maria leveled an electricity grid that was ill-maintained before the storm. (Reporting by Maria Caspani in New York and Rich McKay in Atlanta; Additional reporting by Makini Brice in Washington and Jon Herskovitz in Austin, Texas; Editing by Peter Cooney)
Our Standards: The Thomson Reuters Trust Principles.