Guam weather in September

September is one of the least pleasant months in Guam: highs of 29°C (84°F) and about 278 mm (10.9 in) of rain on average. Nights average 28°C (82°F) and cloud cover 85% (NASA POWER, 2001–2025 averages). The sea averages 30°C (86°F). It is the 2nd wettest month of the year and the 6th warmest. Compared with August, it is about as warm and about as wet; October brings highs of 29°C (84°F) and 231 mm (9.1 in) of rain.

Is September a good time to visit Guam?

least pleasant month Weather score 37/100.

September is one of the least pleasant months for weather in Guam. For better conditions, consider Dec–Jun.

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Does it rain a lot in Guam in September?

Yes, it is one of the rainy months: about 278 mm (10.9 in) falls in an average September. It is the 2nd wettest month of the year.

How warm is Guam in September?

Days average 29°C (84°F) and nights 28°C (82°F).

Guam weather by month

Month	High	Low	Rain	Cloud	Sea	Weather
January	28°C (82°F)	27°C (81°F)	82 mm	64%	29°C (84°F)	best
February	28°C (82°F)	27°C (80°F)	51 mm	61%	28°C (83°F)	best
March	28°C (82°F)	27°C (80°F)	42 mm	57%	28°C (83°F)	best
April	28°C (83°F)	27°C (81°F)	47 mm	49%	29°C (83°F)	best
May	29°C (84°F)	28°C (82°F)	62 mm	52%	29°C (85°F)	best
June	29°C (84°F)	28°C (83°F)	97 mm	56%	30°C (86°F)	best
July	29°C (84°F)	28°C (83°F)	197 mm	77%	30°C (86°F)	fair
August	29°C (84°F)	28°C (82°F)	315 mm	86%	30°C (86°F)	least pleasant
September	29°C (84°F)	28°C (82°F)	278 mm	85%	30°C (86°F)	least pleasant
October	29°C (84°F)	28°C (83°F)	231 mm	73%	30°C (86°F)	least pleasant
November	29°C (84°F)	28°C (83°F)	136 mm	55%	29°C (85°F)	fair
December	29°C (83°F)	28°C (82°F)	69 mm	55%	29°C (84°F)	best

Sources: 2001–2025 monthly averages from NASA POWER (MERRA-2 reanalysis), sea temperature from Open-Meteo Marine. Page updated Oct 31, 2026. How we rate months