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Thunderstorms expected today as Tropical Storm Arthur approaches along the coast

In a prelude to the stormy weather expected later this week, strong to severe thunderstorms began rolling across Western Massachusetts this afternoon, forecasters said.

Strong winds brought down trees and power lines and caused stream flooding in communities, such as Shelburne Falls, Greenfield, and Northfield, according to damage reports fielded by the National Weather Service.

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The thunderstorms came rumbling through as all eyes have been focused on Tropical Storm Arthur, which was still swirling off Florida today, but was expected to sweep swiftly up the East Coast later in the week, potentially ruining holiday fireworks shows and backyard barbecues.

Arthur is projected to develop into a Category One hurricane by the time it arrives off the New England coast. That’s the weakest kind of hurricane, but it is still expected to bring the possibility of “tropical downpours” for the Fourth of July.

“It’s hard to pinpoint the exact timing,” said meteorologist Bill Simpson of the National Weather Service, “but we want to emphasize periods of tropical downpours for Thursday into Friday. The storm passes east of Cape Cod late Friday night, but what’s well out ahead of it ... could be causing problems here.”

Although Arthur will be passing more than 70 miles east of the Cape, the system will push heavy rainfall and potentially damaging winds into the region, he said.

“Generally speaking, winds will have the biggest impact across the Cape and islands,” Simpson said, with gusts reaching up to 45 miles per hour. Wind gusts inland will be weaker - around 30 miles per hour in Boston.

As for rainfall, Simpson said, most of Eastern Massachusetts could expect an inch or two of rain, but “in some areas there will be some bands of higher amounts.”

“We won’t have river flooding, but you could have poor drainage flooding” in urban areas, Simpson said. He also warned that the periods of tropical downpours expected Thursday into Friday could result in low visibility.

Simpson said he didn’t expect winds to be a problem by Friday night, when many Fourth of July fireworks shows are planned, but he said rain might fall and low-hanging clouds could obscure the displays.

The weather could also turn ugly today, with thunderstorms generated by sunshine and a very warm humid air mass rumbling through much of the state, forecasters said. The National Weather Service issued a severe thunderstorm watch, effective until 9 p.m., for Worcester, Middlesex, Essex, Franklin, Hampden, and Hampshire counties.

The thunderstorms are expected to weaken tonight, but the timing of the weakening is uncertain, forecasters said, suggesting that people stay tune to weather reports.

Clouds are expected tonight, as temperatures fall to the mid-70s. After 10 p.m., there is a slight chance of showers and storms, with possible heavy rain. Wind gusts could reach up to 23 miles per hour.

Thursday, showers and storms are likely after 2 p.m. By this point, it is likely the region will be experiencing the effects of Arthur, so periods of heavy rainfall are possible. Temperatures may reach the upper 80s. The chance for showers and storms persists through 11 p.m., with low temperatures in the low 70s.

Friday’s holiday will likely be wet, with storms and showers likely before 2 p.m. and temperatures in the upper 70s. Overnight, there is a chance of showers before 5 a.m. Temperatures may drop to the mid-60s. The Cape could see wind gusts of up to 45 miles per hour, too high for fireworks shows.

After the unsettled weather, the weekend is expected to be a gem.

Both Saturday and Sunday will likely be sunny and clear, with temperatures hovering in the high 70s on Saturday and the low 80s on Sunday. The weekend nights should be clear with temperatures in the mid-60s.

“Just like last weekend,” Simpson said. “Dry. Cool. Nice.”

Kiera Blessing can be reached at kiera.blessing@globe.com. Follow her on Twitter at @kierablessing.
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