By Friday night, Henri was “almost a hurricane,” according to the hurricane center, with maximum sustained winds of 70 miles per hour. The storm is expected to be at or near hurricane strength when it makes landfall on Sunday.

Henri was moving north at nine miles per hour late Friday night and was expected to accelerate in that direction through early Sunday, the hurricane center said.

As of late Friday night, Henri was 230 miles south-southeast of Cape Hatteras, N.C.

Of three storms that recently formed in the Atlantic Ocean, Henri, which developed on Monday off the East Coast of the United States, formed most recently. Most of the attention early this week was on Tropical Depression Fred, which made landfall in the Florida Panhandle on Monday afternoon as a tropical storm, and Hurricane Grace, which came ashore in Haiti as a tropical depression before making landfall as a hurricane on the Yucatán Peninsula in Mexico on Thursday. It made landfall on the east coast of Mexico’s mainland early Saturday.

Henri is expected to dump up to six inches of rain over New England on Sunday and Monday, with isolated totals near 10 inches. Heavy rainfall across the area could bring some flooding. Some coastal areas could experience storm surges as high as five feet.

The National Hurricane Center said on Friday night that “heavy rainfall may lead to considerable flash, urban and small stream flooding” over portions of Long Island and New England on Sunday and Monday.

The National Weather Service in New York said that in Long Island and Connecticut, destructive winds, life-threatening storm surges and heavy rainfall were all likely.

In New York City and parts of New Jersey, there is a chance of winds of 30 to 40 miles per hour on Sunday, according to the Weather Service.

“The most likely arrival time of tropical storm force winds across the tristate area is early Sunday morning,” the Weather Service said in a Friday night briefing. “However, the region could see tropical storm force winds as early as Saturday night.”

When Hurricane Bob hit New England in 1991, it killed at least a dozen people, brought down power lines and wrecked houses as neighborhoods flooded.

Gov. Charlie Baker of Massachusetts said on Friday that residents and vacationers in Cape Cod should leave the area before the storm reached full force on Sunday. He said he was prepared to deploy up to 1,000 National Guard troops to help with evacuations if necessary.

While it is not uncommon for several weather systems to be active at once during hurricane season, forecasters with the National Hurricane Center said, it is somewhat unusual for there to be three at the same time that have prompted tropical storm watches or warnings for land areas.

“It’s a busy period here,” Michael Brennan, the branch chief of the center’s hurricane specialist unit, said on Monday.

The links between hurricanes and climate change are becoming more apparent. A warming planet can expect stronger hurricanes over time, and more of the most powerful storms — though the overall number of storms could drop, because factors like stronger wind shear could keep weaker storms from forming.

Hurricanes are also becoming wetter because there is more water vapor in the warmer atmosphere; scientists have suggested that storms like Hurricane Harvey in 2017 produced far more rain than they would have without the human effects on climate. Rising sea levels are also contributing to higher storm surges, the most destructive element of tropical cyclones.

A major United Nations climate report released this month warned that nations have delayed curbing their fossil-fuel emissions for so long that they can no longer stop global warming from intensifying over the next 30 years, leading to more frequent life-threatening heat waves and severe droughts. Tropical cyclones have probably become more intense over the past 40 years, the report said, a shift that cannot be explained by natural variability alone.

Ana became the first named storm of the season on May 23, making this the seventh year in a row that a named storm developed in the Atlantic before the official start of the season on June 1.

In May, scientists with the National Oceanic and Atmospheric Administration forecast that there would be 13 to 20 named storms this year, six to 10 of which would be hurricanes, and three to five major hurricanes of Category 3 or higher in the Atlantic. In early August, in a midseason update to the forecast, they continued to warn that this year’s hurricane season would be an above-average one, suggesting a busy end to the season.

Matthew Rosencrans, of the National Oceanic and Atmospheric Administration, said that an updated forecast suggested that there would be 15 to 21 named storms, including seven to 10 hurricanes, by the end of the season on Nov. 30. Henri is the eighth named storm of 2021.

Last year, there were 30 named storms, including six major hurricanes, causing meteorologists to exhaust the alphabet for a second time and move to using Greek letters.

It was the highest number of storms on record, exceeding the 28 in 2005, and included the second-highest number of hurricanes on record.

Derrick Bryson Taylor, Neil Vigdor, Jesus Jiménez, Jacey Fortin and Eduardo Medina contributed reporting.