Newark, N.J., Mayor Cory Booker is expected to announce his candidacy for the U.S. Senate seat vacated by Frank Lautenberg, who passed away on Monday.

A source close to Booker told Yahoo News that the Democratic mayor was expected to announce Saturday his intention to enter the special election primary, scheduled for Aug. 13. However, the source warned that the announcement could be delayed by heavy rains and flooding caused by remnants of Tropical Storm Andrea, expected to plague the Northeast over the weekend.

In December, Booker said he was considering a run for Lautenberg’s seat in 2014, Yahoo News reports. While Booker would likely be a front-runner in such a race, the upcoming special election could impede Booker’s senatorial aspirations. Several well-funded legislators have either already announced their candidacy or expressed interest in the vacant Senate seat, further complicating an already competitive Democratic race. For Booker to win, he’d have to find a way to compete financially.

On Thursday, Rep. Rush Holt announced that he planned to run for Lautenberg’s seat, Yahoo News reports. In his statement, Holt described himself as the “best candidate to continue the passionate advocacy for progressive values that Sen. Lautenberg exemplified.” Other potential Democratic challengers include Rep. Frank Pallone and state Assembly Speaker Sheila Oliver, Yahoo News reports.

On the Republican side, the competition has been relatively docile. State Sens. Tom Kean Jr. and Joseph Kyrillos, each of whom has previously run for Senate, have already dismissed speculation that they would pursue the seat. As of Friday, Steve Lonegan, a former mayor of Bogota, N.J., was the only declared candidate for the Republican primary, Yahoo News reports.

Contenders on both sides of the aisle have until Monday to qualify for the primary, which requires a submission of 1,000 signatures of support. The winners of each primary will compete in a special election, set for Oct. 16.