Passengers lifted their feet to avoid getting soaked. One man stood on a seat.

Perhaps more shocking: Just over an inch of rain caused the inundation.

What happened?

On Wednesday, a thundershower hit. That was “certainly not unusual,” Tim Morrin, a National Weather Service meteorologist, said.

What was unusual was the storm’s speed.

A little more than an inch of rain fell on Staten Island in about 20 minutes, according to local weather readings. Mr. Morrin said that speed was “remarkable.”

The total rainfall that day was about 1.71 inches, he said.

Were the people on the bus all right?

Yes.

The rain flooded Richmond Terrace on Staten Island’s North Shore.

More than one Metropolitan Transportation Authority bus driver reported the conditions, according to Shams Tarek , an M.T.A. spokesman. The driver of the bus pictured above evaluated the situation and decided it was safe to proceed, Mr. Tarek said.