The producers used CGI rain for many storm scenes, but did not bother to ensure that the actors in those scenes had wet hair and wet clothing. The result was perfectly-dry people in the midst of deluge.
At one point, our heroes are in a home in Beverly Hills, which suddenly becomes flooded with water...and of course with SHARKS! After the sharks munch on someone, another observes the bloody water in the foyer and exclaims, "It looks like it's that time of the month!"
When our heroes rush out of the shark-infested, flooded house, there's basically no water standing outside the house. But the amount of water inside the house is apparently so significant that... wait for it... the house explodes from the pressure of that water!
Much, much more in which to delight, courtesy of Sharknado. What were your favorite moments? (Don't pretend you were oblivious to the movie-of-the-millennium.)