Subway riders are experiencing mass rush hour suspensions and delays for the second time in two days Thursday, after another power outage caused signal problems at Manhattan’s West Fourth Street station.

As of 9 a.m., the MTA warned of severe disruptions on the B, D, F and M lines. F trains were being rerouted and delays were reported elsewhere. Service on the C line was also shut down. See the latest status updates here.

On Tuesday, the MTA experienced a similar rush hour problem, which it blamed on heat taxing the system. MTA officials said that the outage impacted signals, primarily at three stations — Spring Street C/E, West 4th St-Washington Sq and Broadway Lafayette. Instead of turning green or yellow, signals were getting stuck on red.

At least seven subway lines were affected, and those delays lasted hours.

The reason for Thursday’s outage wasn’t immediately clear, but it comes on the heels of New York City’s second official heat wave this summer — and ahead of afternoon storms that are expected to bring some relief.

Flooding could be a major concern with those storms.