Update: Shortly after 11 pm Sunday, the New York Stock Exchange said it would be completely closed Monday, and likely Tuesday.

For those out there who still doubt whether Hurricane Sandy is the type of once-in-a-lifetime storm against which the only protection is being prepared, the picture below should put all such doubts to rest.

Yes, that's the New York Stock Exchange. And, yes, that's a wall of sandbags put in late Sunday to protect the gilded house of finance from potentially imminent flooding.

For the first time in 27 years, the world's most important stock market is closing its trading floor because of a weather-related event. It is telling traders to stay home Monday and use an alternative electronic network to buy and sell shares.

The NYSE announcement of its decision to cancel physical trading was made remarkably late Sunday -- a little after 4 p.m. EDT -- especially as its parent NYSE Euronext Inc. (NYSE: NYX) had said earlier the same day that the trading floor would remain open Monday. The decision appears to have been made due to pressure by government officials.

NYSE Euronext said the move was made to respect "the actions taken by New York City and State officials to declare a state of emergency, suspend local New York City transportation beginning this evening, and issue evacuations orders in the proximity of the [NYSE] building."

Both city and state officials have been harping on how bad the storm could be all day. Under the worst-case scenario, New York Mayor Michael R. Bloomberg said at a press conference Sunday afternoon, a 12-foot storm surge could cover much of Manhattan's Financial District with several feet of water by noon tomorrow.

Elsewhere in lower Manhattan, Wall Street bigfoots appeared to be hunkering down for the Frankenstorm, as Citigroup Inc. (NYSE: C), Goldman Sachs Group Inc. (NYSE: GS), and JPMorgan Chase & Co. (NYSE: JPM) all told their employees to stay home.