Is the soil sandy and rocky or clay and rocks? water run-off and disappear or does it puddle on the flats?? getting the grass started now is the best option, but I would plan on multiple seedings right upto dormant seeding and Springtime over seeding, because you have no irrigation... is there any shade at all on the property???
Now that I know that clay's texture(platelets) has nothing to do with water infiltration, percolation, or drainage,,, I wonder what does...