Climate Insights for Castletown

The climate in Castletown is temperate. The average annual temperature is 11°C and approximately 1042mm of precipitation falls per year. Castletown receives a notable amount of rainfall throughout the year, including during its driest month. Castletown is in the Northern Hemisphere. Summer begins at the end of June and lasts through September. The summer months are: August, September, July. The coldest months are February, March, January, when temperatures can drop to 6°C.

Castletown has relatively stable temperatures year-round, staying within a 10°C range. August is the warmest month, though highs remain moderate at 16°C with a mean of 15°C. February is the coolest month, with minimum temperatures around 6°C and an average of 7°C. Daily temperature variation is modest, with an average difference of 2°C between highs and lows. The sharpest temperature change occurs between October and November, with a 2°C shift in average temperatures.

Castletown is a moderately rainy area, receiving approximately 1042mm of precipitation annually, which averages out to around 87mm per month. The wettest month is December, averaging 138mm of rainfall. November and October also tend to see above-average precipitation. The driest month is May, with just 50mm. That's 88mm less than December, the wettest month. Precipitation varies noticeably between seasons, with the second half (July to December) of the year generally seeing more rainfall.

Castletown is very windy, with an average annual wind speed of 38km/h. For context, sustained winds below 12km/h are generally light, while anything above 25km/h is considered strong. The windiest month is December, averaging 45km/h, which can feel quite blustery and may affect outdoor activities. The calmest conditions occur in July, with average winds dropping to 31km/h, making it an ideal period for wind-sensitive activities. There is moderate seasonal variation in wind speed, with a 14km/h gap between the calmest and windiest months. Wind tends to be stronger during winter months, driven by seasonal pressure systems. The seasonal averages break down to 45km/h in winter, 35km/h in spring, 32km/h in summer, 40km/h in autumn.

It is currently spring in Castletown, which began on March 20, 2026. Castletown is in the Northern Hemisphere, where spring begins in March, summer in June, autumn in September, and winter in December. The warmest period peaks in August at around 16°C, while the coldest stretch bottoms out in February near 6°C. Summer is next, beginning on June 21, 2026 — 90 days from now.

The best time to visit Castletown is during August, when the weather is most comfortable for travellers. During these months, average temperatures hover around 15°C with modest rainfall averaging 82mm per month. By contrast, February can be quite cold with temperatures dropping to 6°C. Despite being the best months overall, some rain is still likely — pack a waterproof layer and plan a mix of indoor and outdoor activities.

The table below shows monthly climate averages for Castletown based on historical weather data. Min and max temperatures represent typical overnight lows and afternoon highs for each month, shown in degrees Celsius (°C). Precipitation is measured in millimetres (mm) and indicates the average total rainfall per month. Wind speed is the average sustained speed in kilometres per hour (km/h). All values are based on averages from over 10 years of historical weather data. The current month is highlighted for quick reference.