Some people are calling it the Frankenstorm, the result of Hurricane Sandy meeting a winter cold front, and combining with unusually high tides to threaten a vast swath of the East Coast.
New York City is expected to be hit hard on Monday, and the mayor has called for evacuations of much of the city. The transit system is being closed at 7:00 PM on Sunday, anid fears that the subway system may flood. The buses, subway and rail services will remain closed indefinitely, at this point.
The New York Stock Exchange's physical trading floor will be shut. Electronic trading of NYSE stocks will still be open via the fully-automated NYSE Arca exchange until further notice, because the servers are located outside of the potential danger zone. Trading volumes are not expected to be much affected, because the vast majority of trading is now done electronically from all over the globe.
The Exchange had originally planned to remain open, but the decision to close when the area surrounding Wall Street was evacuated. The Exchange has closed only twice before for weather-related situations; once for a snowstorm in 1969, and for Hurricane Gloria in 1986.
The Nasdaq will be open for business as usual, but many of the Wall Street firms are closed due to the evacuation order. These include American Express and other companies located in lower Manhattan.