Metro-North ridership slipped for the fourth consecutive month in January, a decline the railroad blames in part on lower Manhattan businesses forced to relocate in the months after superstorm Sandy hit Oct. 29, officials said Monday.

January rail ridership was down .6 percent compared with January 2012, a decrease of 37,000 riders, Metro-North said.

"This is not a terribly encouraging trend, and we're still seeing a slight decrease in commutation ridership," Robert MacLagger, Metro-North's vice president of planning, told members of the Metropolitan Transportation Authority board at a Monday meeting in Manhattan.

The biggest percentage decrease -- 13 percent -- came on the Pascack Valley and Port Jervis lines west of the Hudson River, MacLagger said. Some 17,000 riders were lost in January compared with the previous January.

MacLagger said much of that dip was caused by the post-Sandy flood-related shutdown of PATH service into Manhattan that continued into late January. Most riders on the two west-of-the-Hudson lines are taken to New Jersey, where they need to connect to the PATH to get into Manhattan.

"We're hoping that's going to turn around in February," MacLagger told the board of the decline. Typically, commuter ridership tallies have a two-month lag time.

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The January decline follows an 18 percent decrease on the Port Jervis and Pascack Valley lines in December compared with December 2011. That translated into a loss of 24,000 riders, from 133,000 in December 2011 to 109,000 in December 2012, according to railroad data.

West-of-the-Hudson commuters say the one-two punch of Tropical Storm Irene in 2011 and superstorm Sandy has forced them to seek out alternative commutes into Manhattan, like driving or taking the bus. Irene forced a three-month shutdown of the Port Jervis line in 2011, when it washed out a 14-mile stretch of rail between Suffern and Harriman.

An additional 20,000 rides were lost in January on Metro-North's busiest commuter lines -- the New Haven, Harlem and Hudson Lines east of the Hudson, officials said. MTA spokeswoman Marjorie Anders said the fare increase on the New Haven line that took effect Jan. 1 also might have had an impact on ridership.

The January rider decrease came on top of a 1.7 percent decline in passengers in December, when 6.9 million rode rail lines east of the Hudson compared with 7.02 million in December 2011.

Anders cautioned about reading too much into the January numbers for the east-of-the-Hudson lines because the month it was being compared with -- January 2012 -- saw a 5.4 ridership surge from the previous January.

"We could not possibly surpass that," Anders said. "For us to come so close is a phenomenal success."

The latest declines throughout the system continued even as some 99 percent of downtown Manhattan businesses reported returning to their office space in early January after flooding caused by surging river flows, MacLagger said.

However, board member Charles Moerdler questioned data claiming that nearly all downtown Manhattan businesses are up and running after Sandy.

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"Much of lower Manhattan is still not back," Moerdler said. "It's still in terrific disarray. The shopkeepers are not there. The stores are still shuttered. It's only coming back now. Anyone who tells you it's back, it isn't."

Despite the effects of Sandy, Metro-North last year boasted its second-highest ridership total in its history, with nearly 83 million rides.

Officials estimate that if Sandy had not touched down, the railroad easily would have surpassed its 2008 record-setting mark of 83.6 million rides.

On Monday, Metro-North formally announced that it will be adding 187 new trains per week come April 7 as it continues the biggest service expansion in its 30-year history. The increase of mostly off-peak and weekend service is on top of the 56 trains added in October.

"By adding off-peak and weekend trains and by adding stops at key stations, we are able to increase frequency and provide faster trip times systemwide," said Metro-North President Howard Permut.