When considering precipitation, many people might assume the wettest location is in a famously rainy city like Seattle or somewhere along the Gulf Coast. The true record holder for the wettest place in the nation, however, is a surprising, remote, and geographically distinct location. This site receives volumes of rain that dwarf the totals of any mainland US weather station.
Defining How “Wettest” is Measured
The designation of the “wettest place” relies on a long-term meteorological standard known as average annual precipitation. This metric is calculated by averaging the total amount of liquid water—rain, melted snow, and other forms—that falls over a period, typically 30 years, to account for natural climate variability. The measurement is taken at a specific point location using instruments like a pluviometer or a tipping bucket rain gauge. This standard is favored over single-event records or total snowfall, as it reflects the consistent climate of a region.
The Location Holding the Record
The location that receives the most consistent and extreme rainfall in the United States is Mount Waialeale on the island of Kauai, Hawaii. Waialeale, a shield volcano that is the second-highest peak on Kauai, holds this title with a staggering historical average. Based on data collected over a 30-year period, the mountain’s summit averages approximately 460 inches of precipitation annually. This amount is equivalent to over 38 feet of water falling every year, making it one of the rainiest spots on the entire planet. While weather station data is not currently collected at the very summit, this long-term average remains the established record for the US.
The Unique Climate Factors
The phenomenal rainfall at Mount Waialeale is a direct consequence of a precise combination of oceanic and orographic factors. The Hawaiian islands sit directly in the path of the steady northeast trade winds, which constantly deliver warm, moisture-laden air across the Pacific Ocean. As this saturated air encounters the steep slopes of the mountain, it is forced upward, a process known as orographic lifting. This rapid ascent causes the air to cool adiabatically, leading to condensation and the formation of dense clouds and consistent rainfall.
The mountain’s height places it just below the trade wind inversion layer, a ceiling of warmer air typically found around 6,000 feet. This inversion layer effectively traps the moisture-rich air below it, preventing the clouds from rising further and causing continuous precipitation directly over the peak. The effect is so localized that the leeward side of Kauai, just 15 miles away, experiences a dramatic rain shadow and receives less than 20 inches of rain annually.
Contiguous US Records
When excluding the unique climate of Hawaii, the wettest parts of the contiguous United States are found in the Pacific Northwest, specifically in the coastal mountain ranges of Washington and Oregon. The record for the mainland is held by a location like Aberdeen Reservoir in Washington State, which records an average yearly precipitation of about 130.6 inches. While this total is substantial and results in lush temperate rainforests, it is less than one-third of the annual rainfall recorded at Mount Waialeale. Other wet areas in the lower 48 states, such as parts of the Gulf Coast, receive significantly less, with the rainiest cities averaging closer to 60 to 67 inches per year.