It should be. Each NOAA transmitter tower should be backed up by generator. In the event the transmitter goes offline (for example, the antennae gets ripped off the tower during a hurricane) nearby towers on one of the other 6 frequencies (there are 7 frequencies available) will go to full power. Any SAME id's for the area covered by the damaged tower will be redistributed to the surrounding towers. This increases the likelyhood of a receiver within the range of the damaged tower can receive an emergency broadcast.

If too many go down in an area at once, you probably already know that something is very wrong.