UPDATE, 11:24 AM: Nielsen confirmed that it has “made a decision not to release November 2012 data for NY” due to Hurricane Sandy, which knocked out too many households in its survey. It also says, in a statement, that it will “continue to evaluate other markets” and “will provide an update on any days that will be excluded.” Nielsen will announce before the November survey period’s over how it plans to handle markets where people use diaries to report their viewing choices. Meanwhile it’s evaluating Local People Meter results for Baltimore, Boston, Cleveland and Philadelphia, but expects to announce by next week that some days will be excluded from the November report. The company adds that while the number of homes in its Local Metered Samples and the National People Meter Sample were “lower than normal,” the survey for the national results “passed its established threshold.” Nielsen will examine the results to identify “any geographic distortion.”

PREVIOUS, 8:20 AM: The problems at the ratings company are “without precedent,” according to a report this morning in Media Post News. The trade publication says that Nielsen has begun to tell clients that it won’t provide November ratings for the New York City area, the No. 1 market with 6.5% of the nation’s viewers, due to the impact of Hurricane Sandy. Meanwhile, Nielsen is trying to determine specific days it can report for New York, Philadelphia, Boston, Cleveland-Akron, and Baltimore. That could complicate billions of dollars worth of ad deals based on network ratings guarantees. The problems flow from the large number of local people meter users who were affected by the superstorm. Boxes were knocked out when homes lost power or were destroyed — or became useless when users had to relocate. The markets affected by the storm could account for 13.4% of all viewers, and are represented in the 20,000 homes in Nielsen’s national people meter sample. Nielsen’s system was hit “during one of the most valuable advertising periods of the television calendar year, the start of a new season, as well as the November sweeps, when ratings for many smaller TV markets are set for an entire quarter,” says MPN editor Joe Mandese. Nielsen wouldn’t say why it has taken so long to determine the extent of the problem, or how it has been able to report national ratings since the storm, he adds. I’ve also reached out to Nielsen and will let you know what the company says when I hear back.