Pool season · New Hampshire
Portsmouth Pool Season: the Year on One Bar
Last updated: July 15, 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.
The 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.
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.