Apparel retailer Express (EXPR) sounded the profit alarm on Tuesday by slashing its third-quarter earnings targets well below Wall Street’s already-lowered expectations due to an “abrupt change in traffic” last month.

The gloomy profit warning sent Express’s shares plunging 17% to new post-IPO lows.

The Columbus, Ohio-based company said it now expects to earn 16 cents to 20 cents a share in the current quarter, down from 27 cents to 32 cents and well below the Street’s view of 29 cents.

Express’s net income projection was slashed to $14 million to $17 million, compared with $23 million to $28 million previously.

Same-store sales are now seen decreasing in the mid-single-digit range.

“While our sales in August were in line with the expectations we provided when we introduced third quarter guidance, trends became increasingly difficult in September driven by an abrupt change in traffic,” CEO Michael Weiss said in a statement.

Weiss also cited “increased promotional activity to maintain our inventory discipline,” but said traffic trends improved in the final week of September “as we conveyed a clearer pricing message to our customers.”

Express said it still expects to report its full third-quarter results during the week of November 26.

The profit warning clearly spooked shareholders, who sent Express’s shares tumbling 17% to $12.50. Even before Tuesday’s tumble the company’s shares had lost 5% of their value since returning to the public markets in May 2010 and about 25% so far in 2012.

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