Mercer Island (WA) Temperatures: Monthly Averages and Year-Round Insights

On this page, we’ll explore Mercer Island’s temperature statistics in detail, including day and night variations and monthly averages. We’ll also compare the annual temperature to other cities in the United States of America.

Monthly Temperature Averages

In Mercer Island, temperatures differ significantly between summer and winter months. Average maximum daytime temperatures range from a comfortable 25°C in August, the warmest time of the year, to a chilly 8°C during cooler months like December. At night, minimum temperatures typically average around 2°C during these months.

The chart below illustrates the average maximum day and minimum night temperatures in Mercer Island by month:

The lowest temperatures typically occur between 4 AM and 6 AM, while the peak temperatures are generally observed around 3 PM, coinciding with the sun’s strongest heating effect. August, the city’s warmest month, enjoys 280 hours of sunshine.

The chart below shows the average temperature throughout the year:

December, the city’s coldest month, receives about 154 mm of rainfall spread over roughly 20 days. For more information, please visit our Mercer Island Precipitation page.

Annual Temperatures in the United States of America Compared

The map below shows the annual temperature across the United States of America. You can also select the different months in case you are interested in a specific month.

Annual

Annual

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Legend

very warm

warm

pleasant

moderate

cold

very cold

Very warm means maximum temperatures above 30°C. Warm: 22°C to 30°C. Pleasant: 18°C to 22°C Moderate: 12°C to 18°C. Cold: 2°C to 12°C. Very cold: lower than 2°C

Mercer Island Temperatures Compared World Wide

Mercer Island’s average annual maximum temperature is 16°C. Let’s compare this with some popular tourist destinations:

Athens, Greece, experiences an average annual temperature of 23°C, with hot summers and mild winters typical of a Mediterranean climate.

Meanwhile, Queenstown, New Zealand, the average annual temperature is significantly lower at 10°C, with mild summers and cold winters.

In Shanghai, China, the annual average temperature is 21°C, offering warm summers and mild winters.

In Tokyo, Japan, the average annual temperature is 21°C, expect warmer summers and milder winters.

How does the temperature feel?

Humidity is an essential factor in how you experience temperature. When a warm period is accompanied by high humidity, it results in a higher perceived temperature. This is especially true when temperatures exceed 25°C, as it can cause greater discomfort.

On the other hand, in cooler months, especially when temperatures dip below 10°C, high humidity can intensify the cold. This makes the air feel much colder than it really is.

In Mercer Island, during the coolest month, December, you will experience 80% humidity, which is considered very high. This is accompanied by an average maximum temperature of 8°C. In the warmest month, August, the humidity is 68% combined with an average maximum temperature of 25°C, which creates a high-feel temperature. Explore our detailed page on humidity levels for further details.

How are these Temperatures Measured?

Generally, temperature data depicting climate is usually given over a 30-year average in order to reduce short-term fluctuations and reveal better long-term trends in climate conditions.

This temperature data is taken from land-based thermometers, ocean buoys, ships, and satellites. These measurements are transmitted to weather stations and climate centers around the globe where they are processed, averaged, and analyzed in order to monitor the trends and create climate models.

Effects of Temperature on Weather and Climate

Temperature variations influence precipitation patterns in Amsterdam:

Rainfall: Warm air holds more moisture, leading to heavier rain during warmer months. However, precipitation is generally moderate year-round.

Snow: Occasional snowfall occurs in winter, though it rarely lasts very long.

For more detailed information about Mercer Island’s weather, including monthly rainfall, sunshine hours, and humidity levels, visit our Mercer Island climate page.