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Summer 2025 Summary – Warmer and Drier Than Average

September 5, 2025

Blue Hill Observatory Summer (Jun-Aug) 2025 Summary:  Summer 2025 temperature was much above average, and there was less precipitation and more sunshine…

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Blue Hill Observatory Summer (Jun-Aug) 2025 Summary: 

Summer 2025 temperature was much above average, and there was less precipitation and more sunshine than expected. The approximated 24-hour mean temperature for summer of 70.2 deg F was 2.7 degrees warmer than the 1891-2020 130-year average for the season, and it was 1.0 degrees warmer than the 1991-2020 30-year average. Summer 2025 tied as the eleventh warmest on record. The average maximum temperature of 80.8 deg F was 1.7 degrees warmer than the 30-year normal, and it was the tenth warmest on record. The average minimum temperature of 61.4 deg F was 0.1 degrees warmer than the 30-year normal, which was the fifteenth warmest on record. There was one four-day heat wave during Summer 2025, on June 22nd-25th, and there were 18 ninety-degree days, which was twelve more than average. Summer 2025 was generally warm during June and July, while much of August was cooler than average. The warmest temperature was 99F on June 24th, which matched the highest temperature ever measured at Blue Hill during June and surpassed the previous record for the date of 91F set in 1914, 1976, and 2013. The lowest temperature was 47F on June 1st. The average water vapor pressure was 18.8 mb, which corresponded to a mean dew point of 62F. This value was higher than the long-term average vapor pressure for summer of 17.6 mb, which corresponds to an average dew point of 60F. The season was drier than average, and the total precipitation was 9.59 inches, which was 2.42 inches less than the 30-year normal. Sixty-five percent of the summer rainfall fell during the wet month, July, while June and August were much drier than average. The greatest amount in 24 hours was 3.85 inches on July 10th, which was forty percent of the seasonal rainfall and was caused by an exceptionally heavy band of rain including a thunderstorm that morning. On that day, 1.35 inches of rain was recorded in a single hour. The minimal effects of distant Hurricane Erin, which passed far offshore on August 21st, brought a trace of precipitation and a peak wind gust to 36 mph from the east-northeast. There were eleven thunderstorm days during summer, which was three fewer than average for the season. The mean wind speed was 9.8 mph, which was the second lowest on record for summer, and the prevailing wind direction was from the south-southwest. The highest wind gust was 52 mph from the west-northwest during the arrival of some briefly cooler air on June 20th. Summer sunshine was above average with 825.8 total hours of bright sunshine, or 64 percent of possible, which was seven percent more than the long-term average for the season.

BHO Warmest Summer (Jun-Aug) Average Maximum Temperature, deg F (1885-2025):

1) 83.0 in 1949
2) 82.9 in 2022
3) 82.4 in 2016
4) 82.1 in 2010
5) 81.5 in 1952
6) 81.3 in 2020
7) 81.0 in 2024
8) 80.9 in 1999
   80.9 in 2005
10) 80.8 in 2025

BHO Lowest Summer (Jun-Aug) Mean Wind Speed, mph (1885-2025):

1) 9.5 in 2023
2) 9.8 in 2025
3) 10.0 in 2019
   10.0 in 2021
   10.0 in 2024
6) 10.1 in 2020
7) 10.2 in 2012
8) 10.3 in 2008
   10.3 in 2009

Mike Iacono
Chief Scientist
Blue Hill Observatory

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Blue Hill Observatory & Science Center · Legal

Data Use & Privacy Policy

Please read the full Policy before accessing Observatory data · Effective January 1, 2025

Notice: By accessing, downloading, or using any Blue Hill Observatory data or services, you unconditionally accept and agree to be bound by this Policy in its entirety. If you do not agree, you may not access or use Observatory data.
Effective January 1, 2025 · Milton, Massachusetts · bluehill.org
Part I — Data Use Policy
§ 01

Ownership and Proprietary Rights

All observational records, compiled datasets, metadata, database structures, and related materials provided by the Blue Hill Observatory & Science Center are the exclusive property of the Blue Hill Observatory & Science Center. The Observatory has maintained continuous weather observations at the summit of Great Blue Hill since 1885, and the entirety of that record — its compilation, structure, curation, and organization — constitutes a proprietary database protected under applicable United States law, including copyright law and common law database protections.

All rights not expressly granted in this Policy are reserved by the Observatory. No access to or use of Observatory data shall be construed as a waiver of any rights or as a license to use data beyond the scope expressly stated herein.

§ 02

Governing Law and Jurisdiction

This Policy shall be governed by and construed in accordance with the laws of the Commonwealth of Massachusetts, without regard to its conflict of law provisions. For interactions with international users, this Policy shall apply to the maximum extent permitted by applicable local law.

Any dispute arising from or related to this Policy shall be subject to the exclusive jurisdiction of the state and federal courts located in Norfolk County, Massachusetts. By accessing Observatory data, all users consent to personal jurisdiction in Massachusetts and waive any objection to the venue or inconvenience of such forum.

§ 03

Permitted Uses

Observatory data are made available for the following limited, non-commercial purposes only:

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All other uses require prior written authorization from the Observatory.

§ 04

Attribution Requirement

Any use of Observatory data in any published, presented, or publicly distributed work must include the following verbatim acknowledgment:

“Data provided by the Blue Hill Observatory & Science Center, Milton, Massachusetts. Continuous weather observations since 1885.”

Failure to include proper attribution is a material violation of this Policy.

§ 05

Prohibited Uses

Unless explicitly authorized in writing, Users may not:

  • Resell, license, sublicense, or commercially exploit Observatory data in any form
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  • Publish the dataset for download by third parties
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§ 06

Commercial Licensing

Organizations seeking to use Observatory data for commercial purposes must obtain a license prior to any such use. Licensing inquiries: data@bluehill.org.

§ 07

Automated Access

Automated scraping, bulk harvesting, or systematic downloading of Observatory data is strictly prohibited without prior written authorization.

§ 08

Enforcement and Remedies

Violation of this Policy may result in immediate revocation of data access, pursuit of legal remedies available under United States law, and referral to applicable authorities. The Observatory reserves all rights to seek injunctive relief, damages, and attorneys’ fees in connection with any unauthorized use of its data.

Part II — Privacy Policy
§ 09–10

Scope & Information Collected

This section governs the collection, use, storage, and disclosure of personal information from visitors to the Blue Hill Observatory website and users of its data services. The Observatory may collect contact information (name, email, organization) when voluntarily submitted, usage data including IP addresses and pages visited, and data download records.

§ 11–12

How We Use Information & Retention

Information is used solely for: responding to inquiries and licensing requests; monitoring and enforcing compliance with this Policy; improving website performance; and communicating Observatory news to opted-in users. The Observatory does not sell, rent, or share personal information with third parties for marketing purposes. Data access records may be retained indefinitely for compliance and enforcement purposes.

§ 13

International Users and Data Transfers

The Observatory is located in the United States. International users acknowledge their information will be processed in the United States under U.S. law. Users requiring specific data processing agreements under non-US law must contact data@bluehill.org before accessing data.

§ 14–16

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Part III — General Provisions
§ 17–20

Modifications, Severability, Entire Agreement & Contact

The Observatory reserves the right to modify this Policy at any time. Updated versions will be posted at bluehill.org. Continued use of Observatory data following any modification constitutes acceptance of the revised Policy. This Policy constitutes the entire agreement between the User and the Observatory. Questions and licensing inquiries: Blue Hill Observatory & Science Center, Milton, Massachusetts — data@bluehill.org

By accessing, downloading, or using any Blue Hill Observatory data or services, you acknowledge that you have read, understood, and agree to be bound by this Policy.
Effective January 1, 2025 · Blue Hill Observatory & Science Center · Milton, Massachusetts
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