The lunar wobble will fuel more severe flooding in the mid-2030s, NASA warns. The Moon's orbit, which affects the Earth's ebb and flow, has a natural "wobble" every 18.6 years, causing extremely high and low tides.
In a new study published in the journal Nature Climate Change, NASA's sea level science team has calculated that the next wobble in the mid-2030s will amplify sea level rise caused by climate change.
Nearly all of the mainland coasts of the United States, as well as Hawaii and Guam, are likely to experience a sharp increase in flooding due to rising sea levels.
However, northern coasts, including Alaska, will be saved for another decade or more as these land areas are being lifted by long-term geological processes, the researchers found.
The study is the first to take into account all known oceanic and astronomical causes of flooding, NASA said.
"The combination of the moon's gravitational pull, sea level rise and climate change will continue to exacerbate flooding on our coasts and around the world."
"It's the effect that accumulates over time that will make the difference," added Phil Thompson, an assistant professor at the University of Hawaii and lead author of the new study.
Tidal floods are less dramatic and contain less water than hurricane storm surges, so they are often viewed as less of a problem.
“But if floods happen 10 or 15 times a month, businesses won't be able to keep going if they're under water,” said Mr Thompson.
"People are losing their jobs because they cannot get to them. Leaking cesspools are becoming a public health problem."
Floods will occur in series that can last a month or more depending on the positions of the Moon, Sun and Earth, NASA officials said.
Because the Moon and Earth are positioned towards each other and towards the Sun in a special way, some city dwellers may see floods every day or two.
Ben Hamlington, who leads NASA's sea level change team, said the research is vital for coastal urban planners, who tend to place more emphasis on preparing for extreme weather events than on chronic flooding.
“From a planning perspective, it's important to know when we will see a rise in water levels,” said Mr Hamlington.
"Knowing that all of your events are grouped in a particular month, or that you may have more flooding in the second half of the year than in the first half, is useful information."
The Moon is currently in the ebb and flow of its 18.6-year wobble, but most US coastlines will not yet see enough sea level rise to notice the effects of flooding.
By the mid-2030s, when the fluctuations next enter the tidal phase, global ocean levels will rise another decade due to climate change.
The study authors predicted results through 2080 by displaying “widely used NOAA scenarios for sea level rise and flood thresholds, the number of times these thresholds were exceeded annually, astronomical cycles, and statistical representations of other processes such as El Niño events that known to affect hot flashes."