Best Time to Dive New Hampshire
Across 6 New Hampshire dive sites with multi-year conditions history, July historically shows the most favorable days — 92% of sampled days in the good band. The next-highest months are August (90%), June (90%) and September (85%). March historically shows the fewest favorable days (53% of sampled days). Average water temperature in the sample runs from about 4°C in February to 18°C in August. Typical seas range from 0.8 m to 1.5 m of significant wave height through the year. These figures are historical climatology computed from measured conditions — patterns, not a forecast or a guarantee.
Computed from our own conditions climatology — measured history, not brochure copy.
Which months are historically most favorable in New Hampshire?
| Month | Historically favorable days | Water temp | Typical seas |
|---|---|---|---|
| Jan | 63% | 6°C | 1.3 m |
| Feb | 57% | 4°C | 1.3 m |
| Mar | 53% | 4°C | 1.5 m |
| Apr | 69% | 6°C | 1.2 m |
| May | 77% | 11°C | 1.1 m |
| Jun | 90% | 15°C | 0.8 m |
| Jul | 92% | 17°C | 0.8 m |
| Aug | 90% | 18°C | 0.8 m |
| Sep | 85% | 18°C | 1.1 m |
| Oct | 74% | 14°C | 1.2 m |
| Nov | 65% | 11°C | 1.1 m |
| Dec | 60% | 8°C | 1.3 m |
% = share of sampled days scoring in the favorable band, median across 6 dive sites with at least two years of history. Ringed = historical peak.
How does this compare worldwide? The Most Reliable Diving Months on Earth ranks 61 countries by the same measure.
Marine life seasons
Sighting patterns across the wider US & Canada — Atlantic coast region — not site-specific promises.
- Scalloped hammerheadAugust
- Great white sharkAug–Sep
- Giant oceanic manta rayJul–Sep
- OrcaMay–Aug
- Humpback whaleJun–Aug
Bars are Jan–Dec — months when sightings historically concentrate (GBIF occurrence records). Wildlife is never guaranteed.
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