U.S. stock index futures opened slightly lower Sunday as traders geared up for another turbulent week while assessing the impact of Hurricane Irene that passed with less damage than feared.

S&P 500 futures fell 3 points and were in line with fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures and Nasdaq 100 futures were unchanged.

(Reporting by Angela Moon; Editing by James Dalgleish)