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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

hotJanFebMarAprMayJunJulAugSepOctNovDecNowNow47%47%7%7%overcastclearprecipitation: 9.3 inprecipitation: 9.3 in0.6 in0.6 inmuggy: 100%muggy: 100%96%96%beach/pool score: 7.1beach/pool score: 7.13.93.9
Guam weather by month. Click on each chart for more information.

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

Average High and Low Temperature in GuamJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F10°F10°F20°F20°F30°F30°F40°F40°F50°F50°F60°F60°F70°F70°F80°F80°F90°F90°F100°F100°FFeb 1285°FFeb 1285°FJun 588°FJun 588°F76°F76°F79°F79°FApr 2688°FApr 2688°FJul 988°FJul 988°FDec 2786°FDec 2786°F78°F78°F78°F78°F77°F77°FNowNow
The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.
AverageJanFebMarAprMayJunJulAugSepOctNovDec
High85°F85°F86°F87°F88°F88°F87°F87°F87°F87°F87°F86°F
Temp.80°F80°F81°F82°F83°F83°F82°F82°F82°F82°F82°F81°F
Low77°F76°F77°F78°F79°F79°F78°F78°F78°F78°F78°F78°F

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

Average Hourly Temperature in GuamJanFebMarAprMayJunJulAugSepOctNovDec12 AM12 AM2 AM2 AM4 AM4 AM6 AM6 AM8 AM8 AM10 AM10 AM12 PM12 PM2 PM2 PM4 PM4 PM6 PM6 PM8 PM8 PM10 PM10 PM12 AM12 AMNowNowwarmhot
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
The average hourly temperature, color coded into bands. The shaded overlays indicate night and civil twilight.
Map
Marker
© Esri, et al.

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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

Cloud Cover Categories in GuamclearerclearercloudierJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%Feb 1847%Feb 1847%Aug 77%Aug 77%Nov 1527%Nov 1527%May 428%May 428%NowNowclearmostly clearpartly cloudymostly cloudyovercast
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.
FractionJanFebMarAprMayJunJulAugSepOctNovDec
Cloudier56%54%55%63%77%83%90%92%90%85%72%61%
Clearer44%46%45%37%23%17%10%8%10%15%28%39%

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

Daily Chance of Precipitation in GuamwetdrydryJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Aug 1267%Aug 1267%Mar 277%Mar 277%Jan 123%Jan 123%Jul 337%Jul 337%Nov 1837%Nov 1837%NowNowrain
The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).
Days ofJanFebMarAprMayJunJulAugSepOctNovDec
Rain5.7d3.8d2.8d2.8d4.5d7.5d15.1d19.9d18.6d15.7d10.5d7.4d

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

Average Monthly Rainfall in GuamJanFebMarAprMayJunJulAugSepOctNovDec0 in0 in5 in5 in10 in10 in15 in15 inAug 229.3 inAug 229.3 inMar 260.6 inMar 260.6 inNowNow
The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average snowfall.
JanFebMarAprMayJunJulAugSepOctNovDec
Rainfall1.7″1.2″0.7″0.8″1.3″2.3″5.6″9.2″8.7″6.5″3.9″2.3″

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 number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.
Hours ofJanFebMarAprMayJunJulAugSepOctNovDec
Daylight11.4h11.7h12.1h12.4h12.8h12.9h12.8h12.5h12.2h11.8h11.5h11.3h

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

Sunrise & Sunset with Twilight in GuamJanFebMarAprMayJunJulAugSepOctNovDec2 AM4 AM6 AM8 AM10 AM12 PM2 PM4 PM6 PM8 PM10 PM12 AMJun 15:52 AMJun 15:52 AM6:52 PMJul 96:52 PMJul 9Nov 205:50 PMNov 205:50 PM6:48 AMJan 246:48 AMJan 24daynightnightSolarMidnightSolarMidnightSolarNoonSunriseSunset
The solar day over the course of the year 2021. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

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

The time in which the moon is above the horizon (light blue area), with new moons (dark gray lines) and full moons (blue lines) indicated. The shaded overlays indicate night and civil twilight.

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

Humidity Comfort Levels in GuamJanFebMarAprMayJunJulAugSepOctNovDec0%0%10%10%20%20%30%30%40%40%50%50%60%60%70%70%80%80%90%90%100%100%Feb 1196%Feb 1196%100%Oct 18100%Oct 18NowNowmiserablemiserableoppressiveoppressivemuggymuggy
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
The percentage of time spent at various humidity comfort levels, categorized by dew point.
JanFebMarAprMayJunJulAugSepOctNovDec
Muggy days30.4d27.0d30.3d29.8d31.0d30.0d30.8d30.9d30.0d31.0d30.0d30.9d

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

Average Wind Speed in GuamwindywindyJanFebMarAprMayJunJulAugSepOctNovDec0 mph0 mph2 mph2 mph4 mph4 mph6 mph6 mph8 mph8 mph10 mph10 mph12 mph12 mph14 mph14 mph16 mph16 mph18 mph18 mph20 mph20 mph22 mph22 mphDec 2617.2 mphDec 2617.2 mphJul 2610.4 mphJul 2610.4 mphOct 3113.8 mphOct 3113.8 mphMay 813.8 mphMay 813.8 mphNowNow
The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Wind Speed (mph)17.017.016.515.113.112.310.910.910.912.415.617.1

The predominant average hourly wind direction in Guam is from the east throughout the year.

Wind Direction in Guam

Wind Direction in GuamJanFebMarAprMayJunJulAugSepOctNovDec0%100%20%80%40%60%60%40%80%20%100%0%NowNowwesteastsouthnorth
northeastsouthwest
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

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

Average Water Temperature in GuamJanFebMarAprMayJunJulAugSepOctNovDec79°F79°F80°F80°F81°F81°F82°F82°F83°F83°F84°F84°F85°F85°F86°F86°F87°F87°FJul 3185°FJul 3185°F81°FFeb 2381°FFeb 23Jun 384°FJun 384°FNov 1284°FNov 1284°FJan 1682°FJan 1682°FApr 582°FApr 582°FNowNow
The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.
WaterJanFebMarAprMayJunJulAugSepOctNovDec
Temperature82°F81°F82°F82°F83°F84°F85°F85°F85°F85°F84°F83°F

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

Tourism Score in Guambest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810106.66.62.72.7NowNowprecipitationprecipitationcloudscloudstemperaturetemperature tourism score
The tourism score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

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

Beach/Pool Score in Guambest timeJanFebMarAprMayJunJulAugSepOctNovDec002244668810107.17.13.93.9NowNowprecipitationprecipitationcloudscloudstemperaturetemperature beach/pool score
The beach/pool score (filled area), and its constituents: the temperature score (red line), the cloud cover score (blue line), and the precipitation score (green line).

Methodology

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

Time Spent in Various Temperature Bands and the Growing Season in GuamJanFebMarAprMayJunJulAugSepOctNovDec0%100%10%90%20%80%30%70%40%60%50%50%60%40%70%30%80%20%90%10%100%0%100%Jan 1100%Jan 1100%Jul 3100%Jul 3NowNowwarmhotcomfortable
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
The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

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

Growing Degree Days in GuamJanFebMarAprMayJunJulAugSepOctNovDec0°F0°F2,000°F2,000°F4,000°F4,000°F6,000°F6,000°F8,000°F8,000°F10,000°F10,000°FJan 390°FJan 390°FJan 30900°FJan 30900°FDec 3111,455°FDec 3111,455°FNowNow
The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

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

Average Daily Incident Shortwave Solar Energy in GuambrightdarkJanFebMarAprMayJunJulAugSepOctNovDec0 kWh0 kWh1 kWh1 kWh2 kWh2 kWh3 kWh3 kWh4 kWh4 kWh5 kWh5 kWh6 kWh6 kWh7 kWh7 kWh8 kWh8 kWhApr 47.0 kWhApr 47.0 kWhAug 103.9 kWhAug 103.9 kWhNov 64.5 kWhNov 64.5 kWhNowNow
The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.
JanFebMarAprMayJunJulAugSepOctNovDec
Solar Energy (kWh)5.46.06.86.96.25.24.23.94.04.14.75.0

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.

Disclaimer

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.

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