Pool season · New Hampshire
Portsmouth Pool Season: the Year on One Bar
Last updated: July 25, 2026 · dates · water temp
Portsmouth's whole pool calendar, condensed: when the water warms, when it cools, and where today falls between those edges. Use the opening guide and closing guide for the step-by-step work; keep this page for the dates.
Portsmouth, NH — 39 swim days a yearThe bar compresses Portsmouth's whole pool year into one lane rope: gray floats for the off-season, hollow teal for the May 15–June 5 opening window, solid teal for swim weeks, hollow amber for the closing stretch that ends September 27. Wherever the today marker sits, the nearest color change is your next appointment.
The Portsmouth pool calendar
Opening — target May 22
Open by May 22 — a two-week head start on the June 5 crossing keeps startup chemistry small and beats the local service rush.
Closing — deadline September 27
The window opens September 17 once water leaves the algae zone; the model deadline is September 27, a week ahead of the October 8 freeze normal.
Estimated water temperature by month
Monthly averages of the site's water model run on Portsmouth's own normals — the shape of a typical year, not a forecast. The widget above shows where the current year actually sits.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 26° | 25° | 31° | 40° | 51° | 60° | 69° | 70° | 66° | 56° | 45° | 34° |
The curve peaks near 70°F — comfortable-water months here usually involve a heater or a solar cover.
Every station tells its own story: compare this curve with Nashua's pool season and Dover's — neighboring normals stations can shift the windows by a week or more. The full ranking lives on the New Hampshire season index.
Portsmouth pool season FAQ
When should I open my pool in Portsmouth, NH?
The site model recommends opening by May 22 — about two weeks before Portsmouth's 7-day mean temperature crosses 61°F, while the water is still too cold for algae. The step-by-step sequence is in the Portsmouth opening guide.
When should I close my pool in Portsmouth?
Winterize by September 27. The model holds the deadline a week ahead of Portsmouth's NOAA 50% first-freeze date, so the plumbing is protected before the first hard night. The full sequence is in the Portsmouth closing guide.
How long is the swim season in Portsmouth?
Portsmouth averages 39 days a year with normal highs of 80°F or better — right on the statewide median. The New Hampshire season index ranks all 4 covered cities by the same metric.
How warm does pool water get in Portsmouth?
An unheated pool near Portsmouth typically peaks around 70°F in high summer and bottoms out near 24°F in winter, never quite reaching the 78°F comfort line without a heater or solar cover. The month-by-month curve above shows the whole cycle; the methodology page explains the ±5°F error bars.
Email me when Portsmouth hits the closing window
Data: NOAA 1991–2020 climate normals via Greenland (3.4 mi); live outlook by Open-Meteo. Attribution: sources · assumptions: methodology.