Annapolis has already reached a "tipping point" with more than 30 nuisance flooding events per year, and Baltimore is expected to surpass that total by 2020, according to a NOAA study published Thursday.
By 2050, a majority of the U.S. coastline will face such frequent coastal flooding because of sea level rise, according to the article in the journal Earth's Future.
The timing varies because not all areas are as prone to flooding. Annapolis has one of the lowest nuisance flooding thresholds at 0.29 meters above a measure known as mean higher high water, the average height of an area's highest daily high tide.
Nuisance flooding occurs in Baltimore an average of 13 times per year, but that frequency is expected to grow quickly. The city is among seven points expected to experience such flooding at least 30 days a year within this decade, according to the study.
"Nuisance" flooding refers to when heavy rain causes flooding of streets and low-lying places in urban areas.
Other areas expected to hit that 30-day tipping point in the 2010s include Port Isabel, Texas; Charleston, S.C.; and Atlantic City, N.J.
A National Oceanic and Atmospheric Administration study published in July found that the frequency of nuisance flooding is increasing faster in Annapolis and Baltimore than anywhere else on U.S. coastline.
"Nuisance flooding" occurred an average 39 days each year in Annapolis from 2007 to 2013, up from an average of just fewer than four days per year from 1957 to 1963, an increase of 925 percent. The frequency increased 922 percent in Baltimore over the same period, going from 1.3 days per year to 13 days per year.