Gamasutra, who spoke to someone with access to NPD data, estimates the figure is between 45,000 and 59,000 units. That's despite NPD including an extra week of sales in January for calculation purposes.
As Gamasutra notes, if its estimate is accurate, the Wii U's January sales in North America were fewer than any month on record for the PS3 or Xbox 360. PS3 sales fell to 82K in both April and May 2007, but, after being launched in November 2006, its January 2007 performance saw it shift 244,000 units at twice the cost of the Wii U's cheapest bundle.
In its recent financial report, Nintendo slashed projections for the Wii U, expecting the console to ship 4 million by the end of March instead of the initially estimated 5.5 million. Despite its flagging performance, Nintendo definitively ruled out the Wii U getting a price cut anytime soon.