Some years, late summers in Baltimore can be partially defined by the proliferation of small, ethereal jellyfish floating around the Inner Harbor.

The jellyfish — Atlantic bay nettles — drift up into the upper reaches of the Chesapeake late in summer when the weather is warm and salinity is high. They need both to be happy, experts said.

Jack Cover, general curator at The National Aquarium, said he thinks it’ll be an “off year” for the jellyfish.

“I think it could be a combination of things. We just don’t know. But we had a really sort of weird seasonal weather here,” Cover said.

Oddly warm weather over the winter, when young nettles would still be little polyps, may have disrupted the population, Cover said, though adding he wasn’t sure.

Even aside from a warmer winter, experts said, the extra rainy start to summer makes it likely Baltimore will have a year without a jellyfish invasion.

The deluge of fresh water from rain lowers the salinity of the harbor. That rain has a “lasting effect on salinity in the upper bay,” said Eric Schott, an associate research professor at the University of Maryland Center for Environmental Science.

And then, because the rain infiltrates into groundwater and feeds streams, larger amounts of freshwater are entering the harbor all summer, keeping the salinity lower for longer.

The National Oceanic and Atmospheric Administration Ocean Prediction Center publishes a daily, experimental map that predicts the probability of encountering an Atlantic bay nettle.

The model has consistently shown low probability in the upper Chesapeake, including in Baltimore, throughout the summer.

There’s no reason to think there won’t be any jellyfish in the harbor as summer rolls into September, but they will likely not be as prolific as some recent summers. In fact, Schott saw a nettle in the harbor between Piers 3 and 4 on Aug. 16.

“I don’t think we’re going to get the numbers this year that we got last year. That’s not a scientific prediction, that’s a guess,” Schott said. “In September, we might start to see more.”

It’s also possible — though less likely, experts agreed — to see an occasional moon jelly wander its way to the Inner Harbor.

If you’re eager to see some bay nettles, though, there are a couple of nearby options.

Going farther south and into the lower Chesapeake Bay means saltier water and a higher chance of seeing the nettles. According recent probability maps published by NOAA, the best chances of encountering a wild bay nettle exist in the waters off Virginia or around Smith Island.

Closer to home, you could always visit the jellyfish exhibit at the National Aquarium. There, the “Jellies Invasion” exhibit features multiple species, including the Atlantic bay nettle, the larger Pacific sea nettle and the quirky upside-down jelly.