NEW YORK — Broadway grosses took a significant tumble in Week 15 (Sept. 1-7) with the exit of Labor Day weekend tourists, the return of students to school after summer break and the tail end of hurricane weather, which whipped New York over the weekend.Those factors spelled bad news at the box office, where grosses plummeted by almost $4 million from the previous week to tally $13,119,534. September invariably is a tough month for Broadway, but the usual post-Labor Day slump was made steeper this year by the weather. Across the board, shows dropped alarmingly. The hardest hit were family- and teen-oriented tuners such as “Mary Poppins” ($447,850), “The Little Mermaid” ($662,814), “Legally Blonde” ($355,830), “Hairspray” ($315,507), “Spring Awakening” ($257,541) and “Monty Python’s Spamalot” ($318,166), all of which registered declines ranging from 39% to 51%. Unsurprisingly, perennial chart toppers “Wicked” ($1,351,513) and “Jersey Boys” ($1,043,538) proved the most resilient, confining their downslides to 11% and 8%, respectively. “Mamma Mia!” ($926,839) also stayed relatively strong with a 12% drop, continuing to benefit from exposure of its bigscreen adaptation. Sole show to post an uptick was “The Phantom of the Opera” ($591,749), which bucked the negative trend by reverting to a normal schedule after missing three performances the previous week. Promising new blood arrived with the start of previews of “Equus,” generating plenty of media coverage for the lead role played by “Harry Potter” star Daniel Radcliffe. The revival of Peter Shaffer’s psychological drama grossed a healthy $271,604 in its first two perfs. In its third week of previews, Dickens adaptation “A Tale of Two Cities” fell 23% to $316,227. The show officially opens Sept. 18 at the Al Hirschfeld Theater. Estimated figures for “Young Frankenstein,” which does not officially report grosses, brought the total to $13,553,134. The 22 musicals grossed $11,876,368 for 90.5% of the Broadway total, with an attendance of 216,948 at 70.8% capacity and average paid admission of $77.28. The five plays grossed $1,243,166 for 9.5% of the Broadway total, with an attendance of 17,473 at 69.4% capacity and average paid admission of $71.15. Average paid admission was $76.66 for all shows.