Starbucks officially has a new CEO, with Brian Niccol taking over the top job Monday. Here are challenges he is facing that have hampered Starbucks' sales and stock price in recent months.

In a new memo, Niccol offers a clinical deconstruction of what’s going wrong at the coffee chain—and hints as to how he plans to make it right.

Niccol says there was a sense around Starbucks that the coffee giant had "drifted from its core." Starbucks CEO Brian Niccol had his first day on the job Monday — and yes, he was in the company's Seattle headquarters.