Tropical Storm Henri is expected to hit New England this weekend, potentially strengthening into a hurricane before it arrives and bringing to Massachusetts damaging winds, rain, and storm surges along the coast.
Henri is expected to bring up to 8 inches of rain and winds as strong as 50 miles per hour to Massachusetts, prompting state officials to warn of power outages that could affect up to 300,000 residents. State officials have canceled some MBTA service and urged people to stay inside on Sunday.
Here are answers to some questions about what we know so far — and what we might expect as the storm approaches the region in the coming days. Forecasters warned that the storm’s path is likely to change.
Will Henri make landfall? And where?
As of 11 a.m. Friday, Henri was forecasted to impact Westerly, RI, along the Rhode Island-Connecticut border, and over Worcester. That marked a shift west from where it was forecasted earlier Friday morning, and it was drifting slowly to the west as of Friday night, meteorologists said.
“It appears that the likely track will bring it north and then north west, away from southern New England over to central Long Island into central Connecticut,” Bill Simpson, a weather service meteorologist said on Friday night.
Will it become a hurricane?
As of late Friday morning, it appeared Henri would strengthen into a hurricane through about the time of landfall.
Henri’s wind speeds are projected to reach up to 75 to 85 miles per hour about 500 miles south of Long Island, Simpson said.
On Saturday night, Henri is expected to move into waters south of New England before it reaches the coast.
Why is the track of the hurricane important?
As hurricanes approach New England, they tend to stratify, or transition into storms that produce wind and rain in certain sections, rather than all around. The weather conditions people experience from storms like this are directly related to their track.
The heaviest wind comes on the east side of the track, while the heaviest rain comes to the north and west of the track.
“If it’s coming up through through eastern Massachusetts, we’re going to get some rain in the Worcester Hills,” Babcock said. “If it’s going up through the Connecticut Valley, then maybe the Berkshires, but certainly not over here in in eastern Massachusetts.”
How windy will it get? What does this mean for Boston?
When Henri reaches the coast on Sunday night, it will generate wind speeds of 70 to 75 miles per hour, Babcock said. By Monday morning, when the center of the storm is projected to be near Worcester, it will generate winds of 45 miles per hour.
In Boston and the surrounding suburbs, the strongest winds would be about 45 to 50 miles per hour, Babcock said, strong enough to cause roof damage, downed trees, some airborne projectiles, power outages, and damage to doors and windows.
“Boston is not going to get the 100-plus mile-per-hour winds that we measured with [Hurricane] Bob, but it is going to be enough wind, certainly similar to what we have with winter nor’easters, so it will be able to cause some damage,” Babcock said.
Worcester, where the center of the storm could be, will not see strong winds, because winds are a lot lighter near the center. The strongest winds will be in Boston and the surrounding suburbs, because Boston is on the east side of the projected track. Along the south coast, storm surge and wind will be factors, while areas to the north and west of Worcester will experience the heaviest rain, with the potential for 3 to 6 inches.
“If the center goes to Worcester, Boston’s the right distance to catch what’s left of those strongest winds,” Babcock said.
How do hurricanes form, anyway?
Hurricanes are fueled by warm ocean water that rises.
Warm water temperatures, typically greater than 80 degrees, provide enough water vapor to fuel a hurricane. The rising air and evaporation over warm waters generate the energy that allows the hurricane to form through strong winds and condensation that causes rain to form and drop down to the surface.
Because there is extremely humid air where Henri is forming, that means a lot of rain, Babcock said.
As the storm moves north and approaches the waters south of New England, it will start losing energy, Babcock said.
What about storm surge?
The wind generated by the hurricane pushes the ocean waters along, creating a storm surge, which is a rise in ocean water over land that is normally dry.
The surge will be focused in Newport, R.I., in addition to Narragansett Bay and Buzzards Bay, Babcock said.
The weather service warned that there is good potential for a storm surge because the storm is taking place during high astronomical tides. Though the extent and locations of the surge depend on Henri’s track, the highest risk of the surge is along the eastern Massachusetts coast, including Cape Cod Bay, forecasters said.
“This storm surge associated with Henri is going to be a dome of water that’s on top of the water that’s already there,” Babcock said. “So that will actually make the water level higher than what the astronomical values would state.”
In Newport, there’s a potential for 3 to 5 feet of storm surge as a result of Henri, Babcock said. However, the question remains whether the surge will take place at astronomical high tide for August on Saturday night at about 8 p.m., or if it takes place six hours later at low tide.
Storm surge flooding could occur, Babcock said, causing damage to some buildings that are right near the coast, beach erosion with heavy surf breaching sand dunes, and it could damage marinas, docks, or boardwalks.
“There’s a lot of heavy duty stuff that could happen if the worst case scenarios happen together,” Babcock said. “Storm surge at astronomical high tide, really at both of those high tides in the evening, Saturday and Sunday evenings. We’re anticipating 3 to 5 feet storm surge where it occurs.”
Babcock emphasized that as Henri approaches, the forecast track is changing. If where it’s expected to make landfall continues shifting west, the area of the strongest surge will also shift further to the west. If that happens, storm surge is likely not to take place or be less significant in Massachusetts and Rhode Island, Babcock said.
“Right now, coastal Rhode Island is the main surge zone, but if it shifts again it will probably shift more so into parts of Connecticut,” Babock said. “That’s the uncertainty that we’re running up against and the challenge that we’re running up against. In an ideal case, the forecast track stays the same run after run after run of the computers. But that’s not happening this time.”
How is a New England hurricane different from one in Florida?
When most people think of hurricanes they think of a circular shape where rain and wind are happening in all directions. That image applies to a hurricane in Florida, where there is tropical air that leaves storm conditions on all sides of its projected track and moves very slowly.
By the time those hurricanes move out of the tropics and reach New England, they have stratified, Babcock said, causing heavy wind and storm surge on the east side of its track and heavy rain to the north and the west.
“This is an actual hurricane, just organized a little differently as it moves further north,” Babcock said.
Correction: Due to a reporting error, an earlier version of this story incorrectly stated the speed of the storm. The Globe regrets the error.