A week ago, heavy rains drove flooding in downtown Baltimore, but by Thursday water levels in the harbor were weirdly low.

By lunchtime Thursday, the base of pylons on the bridges stretching between harbor piers was barely covered by water. Oyster beds outside the National Aquarium breached the surface.

The cause, local meteorologists said, is a combination of high winds and Wednesday night’s super moon, when the moon’s orbit brought it closer to Earth than at any other point in its cycle.

The shift prompted the Baltimore-Washington office of the National Weather Service to issue an unusual low-water advisory Thursday morning. The Baltimore end of the Patapsco River hit low tide at 12:17 p.m., according to the National Oceanic and Atmospheric Administration, and the weather service advisory expired at 2 p.m.

At their lowest just after noon Thursday, waters in Baltimore were 1.3 feet below predicted levels, according to NOAA.

Much of Thursday’s low water was driven by astronomical conditions, said Cody Ledbetter, a meteorologist with the weather service’s Baltimore-Washington division, in an email. He also pointed to a big push from northwest winds, which forced waters to the other side of the Chesapeake Bay.

“When winds perfectly align along the Harbor to push water out into the Chesapeake for long enough, you can get these very low tides,” Ledbetter said.

Wind gusts reached 25 mph Thursday afternoon, down from 30 mph the night before.