Shares of Lululemon Athletica Inc. fell more than 15 percent in morning trading as the Vancouver-based marketer of yoga and active apparel lowered its fourth-quarter sales and earnings guidance based on a weak start in January.

Shares declined $9.10, or 15.3 percent, to $50.50 in the first two hours of Nasdaq trading Monday.

Fourth-quarter earnings guidance was pulled down to between 71 and 73 cents a diluted share from earlier forecasts of between 78 and 80 cents. Revenues, originally expected to come in at between $535 million and $540 million, are now projected to end the period at $513 million to $518 million, with same-store sales now expected to be down in the low- to mid-single-digits versus an earlier expectation of a flat quarter.

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“We were on track to deliver on our sales and earnings guidance through the month of December,” said John Currie, chief financial officer. “However, since the beginning of January, we have seen traffic and sales trends decelerate meaningfully.”

Lululemon on Dec. 10 named Laurent Potdevin, formerly president of Toms Shoes, its new chief executive officer, succeeding Christine Day. Michael Casey was appointed nonexecutive chairman, succeeding founder Chip Wilson. Casey assumes his role in June.

“We are starting to see the results of the significant investments we made throughout this past year to strengthen and enhance our back-of-house product operations structure,” Currie said. “While we realize that it will require continued investment and time to get to best-in-class status, with our new leadership in place we are very focused on building on this stronger foundation to execute our long-term growth strategies.”

Lululemon was hounded throughout 2013 by quality control problems with the Luon fabric used in many of its yoga pants, by comments made by Wilson about the issue and by the arrival of various lower-priced interpretations of its products. Shares declined 22.6 percent during the calendar year to $59.03.