It is called the "king tide," and for the next few days in low-lying areas along the Jersey Shore, Delaware Bay, and as far north as Philadelphia and Trenton along the Schuylkill and Delaware Rivers, this twice-a-year phenomenon could cause flooding.
Not enough that anyone needs to build an ark.
Some experts contend, however, that these higher-than-usual tides - arriving in the region Wednesday and continuing through Friday - offer a preview of what everyday ocean, river, and stream levels could look like years from now.
"What's interesting about the king tides is how they serve as a window into our future. Today's king tides will be tomorrow's daily tides . . . probably in about 20 years," said Danielle Kreeger, science director for the Partnership for the Delaware Estuary.
The Wilmington, Del.-based partnership, part of a national estuary program, is involved in projects and research to protect the estuary that is the tidal Delaware River and Bay and its tributaries.
Ocean tides result from the gravitational attraction of the sun, moon, and Earth. Also known as perigean high tides, king tides occur when the three are most closely aligned.
This alignment occurs twice a year, when the Earth reaches its closet point to the sun during its annual orbit, and the moon reaches its closest point to the Earth during its 27-day orbit. The combination of the two make for extreme water levels.
The "spring" king tide in the area occurred in January. It caused no appreciable damage, officials said.
Adding to the possibility of minor flooding during the king-tide period Wednesday through Friday will be gusty winds and rain expected Thursday, according to the National Weather Service in Mount Holly.
It will take only a "little push" from the wind to cause minor tidal flooding along the oceanfront, Delaware Bay, and the lower Delaware River and its tributaries, meteorologist Patrick O'Hara said.
Kreeger said many scientists concur that sea levels in the Delaware estuary and along the Eastern Seaboard could rise by three to five feet by the end of this century.
Kreeger and others say they want to make residents of flood-prone areas aware of what that could mean in the future.
At the Shore, in Barnegat Inlet off Long Beach Island, the high tide is expected to crest at about three feet Thursday morning - a foot higher than one week ago, said Karen Walzer, public outreach coordinator for the Barnegat Bay Partnership, a Toms River-based estuary-protection group.
The story will likely be the same all along Barnegat Bay and up and down the Jersey Shore, so Walzer's group is inviting people to take before-and-after photographs of the king tide and its effects in areas that are known to routinely flood during weather events such as extreme tides.
Walzer said the "Barnegat Bay King Tide Photo Initiative" will be posted on the partnership's website (bbp.ocean.edu) to try to help researchers and planners better understand the vulnerable geography along the coastline and aid them in making development decisions.
While king tides are not a new phenomenon - they have been widely studied for decades in Australia and other the Pacific regions - in recent years their twice-annual arrival, once in spring and again in fall, has provided environmental groups in the United States with an opportunity to show what higher sea levels could look like across North America.
While some scientists say that scenario is inevitable as part of climate change, others dismiss it as needless alarm over a natural phenomenon.
Still, in some regions, including the West Coast, king tides are being carefully studied for clues to the future.
"For us, the king tide has allowed a teachable moment," said Curt Hart, a spokesman for the Washington State Department of Ecology.
Hart said his state has been working with the University of Washington's Climate Impacts Group for more than six years to educate people about the effects of the king tide on Puget Sound, the nation's second-largest marine estuary in the country after the Chesapeake Bay estuary.
Efforts to track the before-and-after effects of the king tide in Puget Sound provided the template for the photography project in Barnegat Bay, he said.
"It's a great way for people to get involved because people can go outside and really see firsthand what the effects of sea-level rise looks like in their own backyard," Hart said.
Angela Andersen, 42, a resident of Long Beach Township on Long Beach Island, who says she has spent every summer of her life at the New Jersey Shore, said she noticed the effects of the king tide on the barrier island as early as this past weekend.
Flood-prone spots, as at Brant Beach between 70th and 84th Streets, took on water, while most of the wetland areas between the mainland and Long Beach Island were completely submerged by Tuesday afternoon, she said.
"To be able to document an actual before and after, for people who really know a particular area well, is something that really sticks with you when you see it," said Andersen, who serves as Long Beach Township's recycling coordinator and is also education coordinator for the Barnegat Bay Partnership.
Andersen said she had never heard of the king tide phenomenon before, but had noticed past flooding not linked to a particular storm and wondered about it.