South Florida hoteliers expect September to mark the trough of their fortunes. Revenues are down 20 percent regionally, as the industry trudges through the month — traditionally the worst for the hospitality trade. From mom and pop motels to top-end luxury properties, discounting is the norm, but it’s not enough to make up the gap in visitor numbers, according to Smith Travel Research. The market data firm reported that for the week ended Sept. 19, Boward hotel occupancy slipped to 51 percent, down 12 percent from last year, and rates to $81.13, down 20 percent from last year. The weekly occupancy in Palm Beach County fell to 42.1 percent, down 14 percent, and rates to $90.24, down 16 percent, also from the previous year.