Climate and monthly weather forecast
Guam, USA

Guam has a tropical rainforest type of climate (Köppen climate classification Af) with hot and humid conditions throughout the year. Temperature variations are little across the mainly wet and dry seasons. Guam lies in the region of Micronesia in the Pacific Ocean and is an organized United States territory. The engulfment by the ocean, northeasterly trade winds, and low latitudes mainly influence the climate. The location of Guam in the Western Pacific Ocean corresponds to the most prolific tropical cyclone activity with an average of 25 named storms annually.

Guam, the Land of the Chamorro, is a 30-mile long island with a maximum width of 12 miles and an area of 212 square miles. The largest island in Micronesia has its highest elevation at 407 meters on Mount Lamlam. Guam has ample fresh water and diverse marine ecosystems, with a coral reef surrounding the entire island. The proximity to the equator, just 13°north of it, gives ample rain, warm temperatures, and an equal duration of day and night. The topography ranges from cliffs in the north, a hilly landscape in the center, and mountains toward the southern end.

The best time to visit Guam is during the dry season from January to May when the rainfall is moderate compared to the excess of the wet season. January and February are typically the coldest months of the year, with temperatures between 75°F (23.9°C) to 84°F (28.9°C). March to May is less busy than the early part of the dry season and economical on the pocket. The temperatures are on the pleasant side, and the ocean waters are calm. The drop in relative humidity makes the conditions comfortable in the dry season.

The worst time to visit Guam is in the wet season between September to November. The precipitation is substantial, along with high humidity and the possibility of storms. The typhoon season peaks between August and October and poses a constant threat to planned vacations. Humidity makes the heat even worse with a high degree of sweating. Tourists from the American mainland belonging to temperate zones find the conditions uncomfortable. Afternoon thunderstorms are frequent on the island and nearby ocean, which makes outdoor explorations and sea activities challenging. Budget travelers find November to their liking with a dip in rain and storms.

Springtime in Guam, spanning March to May, is characterized by comfortable temperatures ranging from 80°F (26.7°C) to 84°F (28.9°C). The ocean waters remain serene, making it an excellent time for swimming and other marine activities. Rainfall is moderate, with the dry season still in effect, leading to mostly clear skies and reduced humidity. The northeast trade winds blow steadily, with speeds varying from 10mph (16.1km/h) to 20mph (32.2km/h). This season is less crowded, making it perfect for visitors seeking tranquillity.

June to August marks the summer months in Guam. Temperatures usually stay within the 82°F (27.8°C) to 88°F (31.1°C) bracket. While the onset of the wet season begins during this period, the rainfall is not yet at its peak. The surrounding ocean waters maintain a temperature slightly cooler than the land, offering refreshing dips for beachgoers. Wind speeds remain moderate, and occasional storms can be expected, particularly as August approaches.

Autumn, from September to November, is the wettest period for Guam. The island experiences temperatures between 80°F (26.7°C) to 85°F (29.4°C). During these months, the island receives about 80% of its annual rainfall of 98" (2489mm), with rain being a daily occurrence. Humidity levels frequently rise above 84% during nighttime, making conditions muggy. Furthermore, cloud cover is most persistent during this period, and volcanic fog from the nearby island of Anatahan can sometimes envelop Guam.

Winter months in Guam, December to February, initiate the dry season. Temperatures during this period are relatively cooler, ranging from 75°F (23.9°C) to 82°F (27.8°C). The ocean waters act as a natural thermostat, ensuring that temperatures rarely surpass 90°F (32.2°C). The northeast trade winds provide relief, moderating the precipitation levels. Sunshine is abundant, although Guam experiences a high degree of ultraviolet radiation even in these months.

January in Guam marks the beginning of the dry season, transitioning from the wetter end-of-year months. Temperatures during this month typically lie between 75°F (23.9°C) and 84°F (28.9°C). Compared to December, which experiences slightly more rainfall and marginally cooler temperatures, January offers a warmer and drier environment. Weather in January »

February continues the dry season in Guam, mirroring the climate conditions of January. This month, temperatures hover between 75°F (23.9°C) and 83°F (28.3°C). While the range remains similar to January, February often sees slightly cooler nights. Weather in February »

March in Guam sees a subtle transition towards warmer temperatures, signaling the gradual approach of the summer months. Temperatures during March are typically in the range of 77°F (25°C) to 85°F (29.4°C). This slight increase from the cooler conditions of February is welcomed by many as a precursor to the warmer and wetter months ahead. While the entire island maintains a consistent climate due to its relatively small size, March doesn't witness any notable variations in weather conditions across different regions or cities. Weather in March »

April in Guam marks a definitive shift towards the warmer spectrum of the year. The temperatures during this month vary between 78°F (25.6°C) and 87°F (30.6°C). Notably, the higher end of this range approaches the all-time record for the island, which was 96°F (35.6°C) set on April 18, 1971. Weather in April »

May signals the culmination of the dry season in Guam, serving as a transitionary period into the wetter months of the year. Temperatures in May tend to fluctuate between 79°F (26.1°C) and 88°F (31.1°C). This month represents one of the last opportunities for residents and tourists to take full advantage of the drier climate before the onset of the more humid and rainy conditions. Across Guam's compact landscape, the rise in warmth is felt consistently. Weather in May »

June in Guam heralds the official onset of the wet season. During this month, temperatures range from 80°F (26.7°C) to 89°F (31.7°C), showcasing the island's tropical warmth. The consistent rise in humidity, accompanied by more frequent rain showers, characterizes the shift from the dry to wet season. Throughout the entire span of Guam, this change in weather patterns is evident. Weather in June »

July in Guam is characterized by the heart of the wet season, presenting a fusion of warmth and consistent rainfall. Temperatures during this month are typically situated between 81°F (27.2°C) and 90°F (32.2°C), representing some of the year's hottest conditions. Weather in July »

In August, Guam remains deeply entrenched within the wet season. The temperatures during this period hover between 82°F (27.8°C) and 90°F (32.2°C). Along with July, August stands as one of the most humid and rain-drenched months for Guam, asserting the dominance of its tropical rainforest climate. Across the breadth of Guam, the intensity of the rainfall is consistently felt. Weather in August »

September in Guam is emblematic of the late stages of the wet season. During this month, temperatures usually range from 82°F (27.8°C) to 89°F (31.7°C). The frequent downpours and high humidity levels still dominate, though the month serves as a gradual bridge to the eventual decline of the monsoon's intensity. Every corner of Guam is influenced by September's pronounced rainfall. Weather in September »

October in Guam signifies the transitioning phase from the wet to the dry season. The month's temperatures are generally between 81°F (27.2°C) and 88°F (31.1°C). While rainfall continues to be a dominant feature, there's a noticeable decrease in its frequency and intensity as October progresses. Throughout Guam, the effects of the diminishing wet season become more apparent. Weather in October »

November in Guam is a distinct month, serving as the doorstep to the dry season. Temperatures during this period typically fluctuate between 80°F (26.7°C) and 87°F (30.6°C). The reduction in rainfall becomes more pronounced, paving the way for longer dry spells and a marked decline in humidity levels. Across Guam, November's transitional climate is palpable. Weather in November »

December in Guam ushers in the full onset of the dry season. The island experiences temperatures generally hovering between 79°F (26.1°C) and 86°F (30°C). As the month unfolds, rainfall becomes a rarer event, and the familiar high humidity of the wet season noticeably recedes, providing more agreeable conditions. Throughout Guam, December's serene climate is evident. Weather in December »