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Castle Island

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Castle Island Weather, Climate and Best Time to Visit

Data source：Meteostat
Update date：2025-09

Castle Island year round climate

  • Spring (March–May): 5.2–15.6°C on average, mild climate, with more rainfall in March, gradually becoming comfortable from April to May. Common activities: Outdoor walks, cycling. Suggested clothing: Light jacket, long-sleeved shirt, comfortable shoes.
  • Summer (June–August): 20.1–24.6°C on average, warm and humid, moderate rainfall. Common activities: Beach activities, water sports. Suggested clothing: Light and breathable clothing, hat, sunscreen.
  • Autumn (September–November): 8.3–19.0°C on average, pleasant climate, reduced rainfall. Common activities: Hiking, viewing autumn leaves (depending on tree species). Suggested clothing: Comfortable long-sleeved shirts, light jacket.
  • Winter (December–February): 0.5–3.3°C on average, cold, more rainfall, possible snowfall. Common activities: Indoor activities, enjoying winter scenery. Suggested clothing: Warm clothing, thick jacket, hat, scarf, gloves.

Castle Island climatological average

Annual average temperature: approx. 12°C / Annual rainfall: approx. 1070 mm / Summer humidity: 65%–75% / Rainiest month: March

Castle Island monthly average temperature and precipitation

Month
Air temperature (°C)
Precipitation (mm)
January
0.5°C
128.7
February
1.4°C
56.3
March
5.2°C
137
April
9.9°C
71
May
15.6°C
71
June
20.1°C
83
July
24.6°C
105.7
August
23°C
98.7
September
19°C
65
October
14.1°C
56
November
8.3°C
67.7
December
3.3°C
130

Castle Island weather for the next seven days

6/20
Saturday
Patchy rain nearby
26.8°C/15°C
6/21
Sunday
Patchy rain nearby
27.3°C/14.4°C
6/22
Monday
Heavy rain
24.8°C/15.2°C
6/23
Tuesday
Patchy rain nearby
19°C/15.1°C
6/24
Wednesday
Sunny
22.8°C/13.9°C
6/25
Thursday
Partly Cloudy
24.6°C/15.4°C
6/26
Friday
Patchy rain nearby
20°C/14.8°C

Castle Island Frequently Asked Questions and Useful Information for Travel

What is Castle Island known for?

Castle Island in Boston is famous for Fort Independence, one of the oldest fortified military sites in North America, and as a popular recreation spot. Visitors can explore the historic fort, enjoy scenic harbor walks, and visit the beloved Sullivan's restaurant.

How much does it cost to visit Castle Island?

Admission to Castle Island and Fort Independence is free. The park is open daily from 6:30 AM to 7:00 PM.

Is Castle Island worth visiting?

Yes, Castle Island is definitely worth visiting. It offers beautiful walking and hiking loops with fantastic views of planes arriving at Logan Airport and ships in Boston Harbor. It's a perfect spot for leisurely strolls and enjoying the scenery.

Can you swim at Castle Island?

Yes, you can swim at the beaches located near Castle Island, such as Pleasure Bay Beach and M Street Beach. Besides swimming, these areas are great for sunbathing, picnicking, and general water recreation.

What historical significance does Fort Independence hold?

Fort Independence on Castle Island has a rich history, with fortifications dating back to 1623. The current granite fort, completed in 1851, was once known as Castle William and served as a crucial military installation through major historical conflicts.