Torrential rains and spectacular lightning swept through Massachusetts late Thursday, bringing trees down, knocking out power, and forcing thousands gathered for early Fourth of July festivities to evacuate the Esplanade in Boston.
The thunderstorms slammed the Boston area at about 10:45 p.m., lighting up the skies over the Esplanade as concertgoers made an orderly exit from the iconic activities after the evacuation order was issued.
The storms began rolling through parts of Massachusetts this afternoon, and were expected to continue into Friday. About one to two inches of rain was expected Thursday night, said Rebecca Gould, a meteorologist with the National Weather Service in Taunton.
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A severe thunderstorm warning for the Boston metro ended at about 11 p.m.
Those who went to the Esplanade festivities Thursday were met with temperatures in the mid-80s and high humidity, sending many to medical tents for treatment, according to Boston EMS.
The heavy rains brought flash floods in the area of Newburyport and Hampton, N.H. The National Weather Service had issued flash flood warnings for Western Massachusetts into Southern New Hampshire beginning at noon and going through the evening. Urban areas like Boston, where there is poor drainage, are at risk for street flooding.
Areas in the storm’s path Thursday experienced issues including downed trees, power outages, and floods.
Troopers responded to numerous reports of fallen trees that blocked roads, according to State Police spokesman David Procopio. Removal crews handled trees across Route 125 in Andover, and Interstate 91 in Northampton and Hatfield, resulting in lane closures, he said.
Power outages occurred throughout the state, with State Police reporting power losses in Western Massachusetts. Residents of Cambridge and Waltham also reported power outages on social media.
As of 3:47 a.m., NSTAR reported about 9,300 customers without power in the Boston area. About 8,800 National Grid customers were without power, according to its outage map.
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Severe thunderstorm warnings were in place late Thursday for Worcester County as well, where residents are urged to be cautious of hail.
Forecasters say Hurricane Arthur will make its closest pass to New England from Friday night into Saturday morning. Arthur began Thursday as a Category 1 hurricane, the weakest kind, but it grew into a Category 2 hurricane at 9 p.m, according to weather service tracking data.
The concert and fireworks in Boston, which had been scheduled for Friday, were moved to Thursday because of the impending storm.
Arthur is expected to push heavy rains and possible tropical downpours onto Eastern Massachusetts on Friday. The Cape and islands will be at the greatest risk for downpours and strong winds, but the effects will be felt farther inland as well, forecasters said.
“The best chance for storms by Friday afternoon will be in Eastern Massachusetts and Rhode Island. We’re looking at chances of about 85 percent,” said William Babcock, of the weather service.
By Friday evening, tropical storm conditions are possible in most of Massachusetts, meaning winds speeds of over 39 miles per hour, tropical downpours, building seas, and rip currents. Areas of Cape Cod and Nantucket are currently under a tropical storm warning.
“The remnants of Arthur are expected to fully move away by Friday night,” said Kimberly Buttrick of the weather service, leaving sunny, cool weather for Saturday and Sunday.
Forecasters said mariners should be wary, issuing a hurricane warning for some areas off the coast, predicting seas building to 19 to 34 feet on Friday night on Georges Bank before subsiding Saturday.
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The forecasters also issued a tropical storm warning for the ocean just south and southeast of Massachusetts, saying boats should be secured and mariners should remain in port.
Beachgoers should still be cautious this weekend, Buttrick said. There is a high risk of rip currents as Arthur churns away from the coast.
Saturday, temperatures should hover in the low 80s with full sun during the day. Overnight is expected to be clear, with temperatures in the low 60s.
Sunday is expected to be sunny as well, with temperatures in the low 80s. Clouds may move in by Sunday evening, with temperatures in the upper 60s.
Related coverage:
• Storms affect Boston Pops concert, fireworks
• Photos: Boston’s Fourth celebration
• Graphic: What makes fireworks pop
• Why Americans love to declare independence
• Photos: Independence Day celebrations through the years
• Guide to Fourth of July in Boston
Kiera Blessing can be reached at kiera.blessing@globe.com.