How was it known that the Twin Towers were about to come down?

On 9/11, city officials predicted the collapse of both the Twin Towers and Building-7. In the case of Building-7, hours in advance.

These predictions were very curious and difficult to rationalize, but very accurate. How was this prediction possible given that the Twin Towers were designed and constructed to tolerate serious fires AND a civil airliner collision.

Listen to first hand accounts of these predictions in this short video -