Climate and Average Weather Year Round in Guam Guam
In Guam, the wet season is overcast; the dry season is partly cloudy; and it is hot, oppressive, and windy year round. Over the course of the year, the temperature typically varies from 76°F to 88°F and is rarely below 74°F or above 90°F.
Based on the beach/pool score, the best time of year to visit Guam for hot-weather activities is from mid December to late April.
Climate in Guam
The temperature in Guam varies so little throughout the year that it is not entirely meaningful to discuss hot and cold seasons.
Average High and Low Temperature in Guam
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in Guam
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
In Guam, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.
The clearer part of the year in Guam begins around November 15 and lasts for 5.6 months, ending around May 4.
The clearest month of the year in Guam is February, during which on average the sky is clear, mostly clear, or partly cloudy 46% of the time.
The cloudier part of the year begins around May 4 and lasts for 6.4 months, ending around November 15.
The cloudiest month of the year in Guam is August, during which on average the sky is overcast or mostly cloudy 92% of the time.
Cloud Cover Categories in Guam
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Guam varies very significantly throughout the year.
The wetter season lasts 4.5 months, from July 3 to November 18, with a greater than 37% chance of a given day being a wet day. The month with the most wet days in Guam is August, with an average of 19.9 days with at least 0.04 inches of precipitation.
The drier season lasts 7.5 months, from November 18 to July 3. The month with the fewest wet days in Guam is March, with an average of 2.8 days with at least 0.04 inches of precipitation.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in Guam is August, with an average of 19.9 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 67% on August 12.
Daily Chance of Precipitation in Guam
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Guam experiences extreme seasonal variation in monthly rainfall.
Rain falls throughout the year in Guam. The month with the most rain in Guam is August, with an average rainfall of 9.2 inches.
The month with the least rain in Guam is March, with an average rainfall of 0.7 inches.
Average Monthly Rainfall in Guam
The length of the day in Guam varies over the course of the year. In 2021, the shortest day is December 22, with 11 hours, 20 minutes of daylight; the longest day is June 21, with 12 hours, 55 minutes of daylight.
Hours of Daylight and Twilight in Guam
The earliest sunrise is at 5:52 AM on June 1, and the latest sunrise is 56 minutes later at 6:48 AM on January 24. The earliest sunset is at 5:50 PM on November 20, and the latest sunset is 1 hour, 2 minutes later at 6:52 PM on July 9.
Daylight saving time (DST) is not observed in Guam during 2021.
Sunrise & Sunset with Twilight in Guam
The figure below presents a compact representation of key lunar data for 2021. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
Moon Rise, Set & Phases in Guam
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The perceived humidity level in Guam, as measured by the percentage of time in which the humidity comfort level is muggy, oppressive, or miserable, does not vary significantly over the course of the year, staying within 2% of 98% throughout.
Humidity Comfort Levels in Guam
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Guam experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 6.3 months, from October 31 to May 8, with average wind speeds of more than 13.8 miles per hour. The windiest month of the year in Guam is December, with an average hourly wind speed of 17.1 miles per hour.
The calmer time of year lasts for 5.7 months, from May 8 to October 31. The calmest month of the year in Guam is September, with an average hourly wind speed of 10.9 miles per hour.
Average Wind Speed in Guam
The predominant average hourly wind direction in Guam is from the east throughout the year.
Wind Direction in Guam
Guam is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature does not vary significantly over the course of the year, remaining within 2°F of 83°F throughout.
Average Water Temperature in Guam
To characterize how pleasant the weather is in Guam throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit Guam for general outdoor tourist activities is from early January to early April, with a peak score in the third week of February.
Tourism Score in Guam
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Guam for hot-weather activities is from mid December to late April, with a peak score in the second week of March.
Beach/Pool Score in Guam
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
Temperatures in Guam are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.
Time Spent in Various Temperature Bands and the Growing Season in Guam
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
Growing Degree Days in Guam
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.
The brighter period of the year lasts for 2.4 months, from February 28 to May 10, with an average daily incident shortwave energy per square meter above 6.4 kWh. The brightest month of the year in Guam is April, with an average of 6.9 kWh.
The darker period of the year lasts for 4.0 months, from July 5 to November 6, with an average daily incident shortwave energy per square meter below 4.5 kWh. The darkest month of the year in Guam is August, with an average of 3.9 kWh.
Average Daily Incident Shortwave Solar Energy in Guam
For the purposes of this report, the geographical coordinates of Guam are 13.479 deg latitude, 144.818 deg longitude, and 0 ft elevation.
The topography within 2 miles of Guam is essentially flat, with a maximum elevation change of 0 feet and an average elevation above sea level of 0 feet. Within 10 miles is also essentially flat (0 feet). Within 50 miles is also essentially flat (0 feet).
The area within 2 miles of Guam is covered by grassland (46%) and cropland (41%), within 10 miles by water (69%) and cropland (16%), and within 50 miles by water (98%).
This report illustrates the typical weather in Guam, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
The details of the data sources used for this report can be found on the Antonio B. Won Pat International Airport page.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.