Guam Monthly Rainfall & Precipitation
This page shows both the average monthly rainfall and the number of rainy days in Guam, Micronesia. Long-term data from 1990 to 2020 was used to calculate these averages. Now, let's break down all the details for a clearer picture.
Guam has a relatively rainy climate with high precipitation levels, averaging 2128 mm (84 in) of rainfall annually. Despite the high annual total, it does experience a distinct rainy season during certain months. Examine our detailed charts below to understand these seasonal patterns.
Monthly Precipitation Levels
The average number of days each month with precipitation (> 0.2 mm (0.01 in))
Guam can be quite wet during August, receiving approximately 362 mm (14 in) of precipitation over 20 rainy days.
In contrast March, experiences much drier conditions, with 59 mm (2.3 in) of rainfall, spread across 20 rainy days.
August, the wettest month, has a maximum daytime temperature of 30°C (86°F). The city receives 143 hours of sunshine in this period. During the driest month March you can expect a temperature of 28°C (82°F). For more detailed insights into the city's temperatures, visit our Guam Temperature page.
Daily Historical Precipitation
50-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in July
Explore Guam's Historical Precipitation: 1976-2026
Browse day-by-day precipitation records for Guam spanning 51 years. Select any month and year to see actual rainfall and snowfall recorded on each day.
Annual Rainfall in Micronesia: City Comparison
The map below shows the annual precipitation across Micronesia. You can also select the different months in case you are interested in a specific month.
heavy rainfall
high
moderate
low
almost none
Guam vs World: Rainfall Compared
Guam's average annual precipitation is 2128 mm (84 in). Let's compare this to some popular worldwide tourist destinations:
In Toronto, Canada, annual precipitation averages 964 mm (38 in), with snowy winters and rainy summers.
In Shanghai, China, the annual average precipitation is 1347 mm (53 in), with a humid subtropical climate.
Melbourne, Australia, has 690 mm (27 in) of rainfall annually, spread fairly evenly throughout the year.
Kuala Lumpur, Malaysia, receives 2529 mm (100 in) of annual rainfall, characteristic of its equatorial tropical rainforest climate, with consistent rainfall throughout the year and peak months during March and November.
Precipitation amounts are measured using specific gauges installed at weather stations, collecting both rain and snow and any other type of precipitation. Rainfall is measured directly in millimeters, while that from snow and ice is obtained by melting it. Automated systems often incorporate heaters to make this easier.
Information from these stations is transmitted via Wi-Fi, satellite, GPS, or telephone connections to central monitoring networks. This information is immediately updated and integrated into weather models and forecasts.
- The U.S. has a significant number of thunderstorms every year, with over 14.6 million taking place across the world annually.
- Approximately 70% of lightning bolts strike land rather than oceans.
- A storm named John was the longest-lasting Pacific tropical storm, continuing for 31 days. As it crossed the dateline twice, it changed status from a hurricane to a typhoon and back to a hurricane.
For more detailed information about Guam's weather, including sunshine hours, humidity levels, and temperature data, visit our Guam Climate page.
