They are filming a weather warning.
People filming.
They are filming is rephrased as people filming
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_film(e1) & n_warning(x2) & of(x2,x1) & n_weather(x1) & n_thing(x1))
exists e1 x1 x2.(a_topic(x1) & Actor(e1,x2) & v_film(e1) & (x1 = x2) & n_people(x1))