Massachusetts and Rhode Island declared emergencies and Boston recorded unprecedented rainfall as storms pounded the U.S. Northeast for a second day today.

Massachusetts Governor Deval Patrick mobilized about 1,000 National Guard troops because of the threat of "beach erosion, major flooding and widespread road closures," according to a statement on his Web site yesterday.

"In some cases there has been two months of rain in the matter of a few days," Tom Kines, a senior meteorologist for AccuWeather Inc., said in a telephone interview. "When you get that much rain over a few-day period, that spells trouble."

Boston's Charles River is set to break the record crest of 9.24 feet reached in August 1955 after two hurricanes dumped more than 26 inches of rain on the region in less than two weeks, according to the National Weather Service.

In Rhode Island, where officials warned of "historic flooding," Governor Donald Carcieri urged residents to leave work early and head home, said a spokeswoman, Amy Kempe.

As much as 8 inches of rain is expected in parts of Rhode Island before the three-day storm ends tomorrow, with the Pawtuxet and Blackstone basins hardest-hit, said the state's Emergency Management Agency. Boston's Logan Airport set a single-day record for rain after 1.96 inches fell yesterday, breaking the high of 1.85 inches set in 1984.

Storm Upon Storm

Flooding in the Northeast from two storms earlier this month caused more than $10 million in damage, drove residents from their homes as power failed and sewer systems backed up, and washed out a section of the Massachusetts Bay Transit Authority's Green Line light rail service.

An AccuWeather meteorologist, Jesse Ferrell, posted a radar loop showing, by his count, 22 storms hitting the Northeast since the official start of the winter season Dec. 1, with almost double the average amount of moisture.

"The rain is still coming down very heavily and it has caused major street flooding, major street closures, throughout" Rhode Island, said Kempe. "The governor is recommending that individuals consider leaving work early to head home."

Mandatory evacuations are under way in the state, although Kempe said she did not know how many. State officials are monitoring Interstate 95, which runs from Maine to Florida, and will close it if necessary, she said.

Rivers Rise

The Pawtuxet River in Cranston, Rhode Island, set a flooding record of 15.07 feet at 9:45 a.m. and is expected to reach 17.5 feet by tomorrow, according to the weather service.

The weather service projects the Charles River at Dover, Massachusetts, will reach 9.9 feet on April 1. The 1955 storms and flooding killed at least 180 people and caused more than $650 million in damage, including the complete or partial failures of more than 200 dams in southern New England, according to the National Weather Service.

Both Boston and Providence, Rhode Island, have set records this month for the wettest March in history, AccuWeather said. An additional 1.06 inches had fallen at Logan Airport as of 10 a.m. today, according to the National Weather Service.

March 2010 is already the fourth wettest-month in Boston history and may become the second-wettest.

New York City had received a monthly total of 10.16 inches by early today, heading toward the March record of 10.54 inches set in 1983.

About 150 people have evacuated their homes in the Fall River area in southeast Massachusetts because of flooding, said Peter Judge, a spokesman for the state's Emergency Management Agency. Record flooding is forecast on the Sudbury and Assabet rivers, he said.

"Every river in central and eastern Massachusetts is expected to be at well-above flood stage before this storm is over," Judge said.