From the Spaceflight Meteorology Group:

The National Weather Service has issued a Flood Advisory that includes JSC and NASA Ellington Field until 9:15 AM.

As of 4:25 AM 1.05″ of rain has fallen at JSC since midnight and 1.16″ at NASA Ellington.  Another 3 to 4 inches is possible over the next few hours. Minor street flooding and ponding of water on-site is likely to begin soon.