The 30-Day Countdown

For a whole month, I've had the same dream. In the dream, my deceased Grandpa looks at me anxiously, repeating the same words... Hide! 30 days left! Hide! 29 days left! Hide! 28 days left! I wake up startled from the dream and tell my family, only to find out that my younger brother has had the exact same dream! What message is Grandpa trying to send us? Until the last day comes...