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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): 41–60°F 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): 68–76°F on average, warm and humid, moderate rainfall. Common activities: Beach activities, water sports. Suggested clothing: Light and breathable clothing, hat, sunscreen.
  • Autumn (September–November): 46–66°F 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): 32–37°F 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. 53.6°F / Annual rainfall: approx. 1070 mm / Summer humidity: 65%–75% / Rainiest month: March

Castle Island monthly average temperature and precipitation

Month
Air temperature (°F)
Precipitation (mm)
January
32.9°F
128.7
February
34.5°F
56.3
March
41.4°F
137
April
49.8°F
71
May
60.1°F
71
June
68.2°F
83
July
76.3°F
105.7
August
73.4°F
98.7
September
66.2°F
65
October
57.4°F
56
November
46.9°F
67.7
December
37.9°F
130

Castle Island weather for the next seven days

6/20
Saturday
Patchy rain nearby
80.2°F/59°F
6/21
Sunday
Patchy rain nearby
81.1°F/57.9°F
6/22
Monday
Heavy rain
76.7°F/59.4°F
6/23
Tuesday
Patchy rain nearby
66.2°F/59.1°F
6/24
Wednesday
Sunny
73°F/57°F
6/25
Thursday
Partly Cloudy
76.2°F/59.7°F
6/26
Friday
Patchy rain nearby
68°F/58.6°F

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.