The Bombay Stock Exchange benchmark Sensex today fell by 88 points as investors turned cautious ahead of a long weekend amid weak global trends. The 30-share barometer settled at 16,613 points.The wide-based National Stock Exchange index Nifty fell by 27 points to 4,958.95 points.Brokers said investors were reluctant to enlarge their positions ahead of a long weekend as the market is closed on Monday for 'Dussehra' festival.