As mall owners prepare to report fourth-quarter earnings results, investors already are bracing for a tougher road ahead, according to a Wall Street Journal analysis yesterday. Real estate researcher Green Street Advisors is lowering its forecasts for the rent that large U.S. mall owners will be able to charge and the amount of space that will be occupied by tenants for years to come. Rents will grow at a paltry 1.5 percent annually for existing nonanchor tenants through 2019, Green Street now predicts, down from the 2.5 percent growth it anticipated a year ago for the same four-year period. Last January, the Newport Beach, Calif.-based researcher predicted that the occupancy rate for nonanchor tenants would rise above 96 percent in 2019. Now it expects that rate to drop to just over 94 percent by then. The occupancy rate in 2015 was nearly 95 percent.