Park climate1991–2020 climate normals71 m source elevationNASA POWER

Monthly temperature, precipitation, humidity, and daylight averages derived from NASA POWER data.

Twelve-Month Climate Normals for Boston Harbor Islands National and State Park, Massachusetts

Name: Boston Harbor Islands National and State Park monthly climate normals
Creator: NASA POWER

Detailed atmospheric profile for Boston Harbor Islands National and State Park providing long-term climate normals for the 1991 to 2020 period. This dataset tracks mean temperatures, average daily precipitation, relative humidity, wind speeds, and daylight hours at a single representative coordinate. These values reflect climatological trends rather than current weather conditions or local site-specific microclimates.

View park overview Browse climate zones

A stylized digital illustration of a coastal landscape with rocky ruins in the foreground, small islands and lighthouses in the distance, and a pastel sunset sky.

Annual climate pattern

Analysis of twelve month average temperatures alongside parallel daily precipitation rates from 1991 to 2020

Boston Harbor Islands National and State Park Annual Climate Normals and Monthly Temperature Patterns

Average monthly temperatures span from sub-zero winter minimums to warm summer highs across the calendar year at a representative coordinate within Boston Harbor Islands National and State Park. Average daily precipitation rates remain relatively steady across all twelve months within the documented NASA POWER climatology period.

Mean temperatureAverage minimum–maximum rangePrecipitation

Annual mean: 9.3 °C
Warmest month: July
Coolest month: January
Wettest month: October

Twelve-month climate

Twelve month comparison of temperature bounds, precipitation rates, humidity, wind, and daylight

Boston Harbor Islands National and State Park Monthly Climate and Weather Patterns

Evaluating average monthly temperature ranges alongside daily precipitation rates clarifies the long term environmental cycle across the calendar year. Tracking relative humidity, wind speed, and calculated daylight hours at a representative coordinate provides complete climatological context without relying on annual averages.

	Mean temperature	Precipitation	Humidity	Wind speed	Daylight
January	-3.6 °C-18° to 11.5°	2.9 mm/day	88%	3.3 m/s	9.3 hours
February	-2.7 °C-16.3° to 10.7°	3 mm/day	86.6%	3.4 m/s	10.3 hours
March	1.2 °C-12.2° to 15.8°	3.7 mm/day	83.4%	3.2 m/s	11.7 hours
April	7.2 °C-3.5° to 22.2°	3.5 mm/day	79.5%	2.8 m/s	13.2 hours
May	13.3 °C2° to 27.2°	2.9 mm/day	78.7%	2.3 m/s	14.4 hours
June	18.6 °C7.5° to 30.4°	3.5 mm/day	78.5%	2 m/s	15 hours
July	22.2 °C12.8° to 32.6°	2.9 mm/day	74.3%	1.9 m/s	14.7 hours
August	21.7 °C11.7° to 33°	3 mm/day	72.8%	1.9 m/s	13.7 hours
September	17.7 °C5.9° to 31°	3.4 mm/day	74.5%	2.1 m/s	12.2 hours
October	11.1 °C-0.4° to 24.7°	3.8 mm/day	78.1%	2.5 m/s	10.8 hours
November	5 °C-5.9° to 18.8°	3.4 mm/day	81.6%	2.7 m/s	9.6 hours
December	-0.2 °C-12.6° to 13.6°	3.7 mm/day	85.7%	3 m/s	9 hours

Compare two months

See two months side by side and how much they differ. Both use the same 1991–2020 climate normals and NASA POWER data point as the table above, so they show typical conditions, not a forecast.

First month

Second month

Mean temperature: January: -3.6 °C; July: 22.2 °C; Change from January to July: +25.9 °C
Precipitation: January: 2.9 mm/day; July: 2.9 mm/day; Change from January to July: 0 mm/day
Daylight: January: 9.3 hours; July: 14.7 hours; Change from January to July: +5.5 hours

Calculated climate highlights

Warmest, coolest, wettest, and windiest monthly averages across stored climatology records

Boston Harbor Islands National and State Park Calculated Climate Highlights

Calculated monthly normals reveal temperature, precipitation, humidity, wind, and daylight contrasts across twelve long-term reference periods. These comparative averages summarize annual patterns without representing observed weather extremes or localized conditions.

Warmest month: July22.2 °C
Coolest month: January-3.6 °C
Wettest month: October3.8 mm/day
Driest month: May2.9 mm/day
Most humid month: January88%
Windiest month: February3.4 m/s
Longest daylight: June15 hours

Interactive climate map

National park climate map

Open the climate map to compare monthly temperature, precipitation, and other averages.

Global National Park Climate Map

Other park climates

Analyze monthly temperature, precipitation, wind, and daylight patterns across diverse regional park settings.

Compare Boston Harbor Islands National and State Park Climate With Other Protected Area Profiles

Examine long-term monthly climate normals to contrast annual temperature and precipitation rhythms across different protected landscapes. Standardized monthly metrics offer a structured way to evaluate atmospheric variation from coastal reserves to inland environments.