One of the Federal Reserve's top central bankers announced his intention to resign on Wednesday, sending a letter to President Donald Trump indicating that he plans to step away for "personal reasons."

Stanley Fischer, who was tapped by former President Barack Obama in 2014 to serve as vice chairman of America's central bank, said in the brief missive that he will remain in his position until Oct. 13, at which point he will walk away. The news generally came as a surprise, as Fischer was already due to be either reappointed or replaced in 2018.

"It has been a great privilege to serve on the Federal Reserve Board and, most especially, to work alongside Chair [Janet] Yellen as well as many other dedicated and talented men and women throughout the Federal Reserve System," Fischer wrote. "During my time on the Board, the economy has continued to strengthen, providing millions of additional jobs for working Americans."

Fischer's exit more immediately opens up a position on the Fed's Board of Governors that Trump will have the opportunity of filling with the Senate's blessing. Three vacancies now exist on the board, and Yellen's and Fischer's scheduled term conclusions in 2018 already meant that Trump would have the opportunity to select five of its seven members.

Fischer's resignation doesn't change that, but it is likely to speed up the appointment process. Once Fischer leaves, the Fed board will consist of only three members, unless Trump finds replacements that meet Senate approval. Trump has decided on one board nominee – Randal Quarles, the head of private investment company The Cynosure Group – but Fischer's replacement to this point remains unknown.

Meanwhile, any Senate confirmation process could be complicated by lawmakers' pending debt-limit and government-spending deadlines, in addition to the White House's push for meaningful tax reform deliberations to begin in the coming months.

Future monetary policy decisions also have potentially been thrown into uncertainty by Fischer's departure. The Fed was expected to announce it would begin selling off assets on its balance sheet later this month, and analysts still expect at least one more interest rate increase before year's end.