News outlets close to the catastrophe seem to be using the term "evacuee," for whatever semantics are worth at a time like this.
I've been thinking about long-term relief when considering where to send my charity, since orgs like the Red Cross and the Salvation Army are likely being overwhelmed by their current cash flow. Here are two organizations that I think are worthy of your consideration. The first one is even based here in Lancaster County.
Mennonite Disaster ServiceHabitat For Humanity