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Ten-year floods have a 10% chance of occurring in any given year (P e =0.10); 500-year have a 0.2% chance of occurring in any given year (P e =0.002); etc. The percent chance of an X-year flood occurring in a single year is 100/X. A similar analysis is commonly applied to coastal flooding or rainfall data.
During El Niño events, precipitation averages about 10 percent above normal, while La Niña events lead to precipitation amounts which average close to 10 percent below normal. [79] Pago Pago harbor in American Samoa has the highest annual rainfall of any harbor in the world. [80] This is due to the nearby Rainmaker Mountain. [80]
The United States tropical cyclone rainfall climatology concerns the amount of precipitation, primarily in the form of rain, which occurs during tropical cyclones and their extratropical cyclone remnants across the United States. Typically, five tropical cyclones and their remnants impact the country each year, contributing between a tenth and ...
That’s a storm that NOAA says has a one-in-500 chance of happening in a given year. Floyd dropped 18.30 inches of rain on Southport in 1999, while Florence’s 31.26 inches of rain over four ...
North Carolina bore the brunt of the storm. [60] Heavy precipitation fell in the eastern portion of the state, peaking at 24.06 in (611 mm) near Southport. [24] Numerous rivers experienced at least 500-year floods, causing extensive flooding.
The county is currently using 500-year flood maps to indicate areas where residents should be ready to evacuate. "We are using the 500-year flood plain maps as kind-of a guide.
For example, a 10-year flood has a 1/10 = 0.1 or 10% chance of being exceeded in any one year and a 50-year flood has a 0.02 or 2% chance of being exceeded in any one year. This does not mean that a 100-year flood will happen regularly every 100 years, or only once in 100 years. Despite the connotations of the name "return period".
So rare was Tuesday's rain between 5 p.m. and 8 p.m. in Sarasota that it should only be expected every 500 to 1,000 years. The Tampa Bay area can normally expect 7.3 inches in the entire month of ...