| Mile Beach | Maine | James Bay | 15.2°C(59.4°F) | July, August, September, October | Live SST → |
| Mile Rock Beach | California | Coastal Waters | 14.5°C(58.1°F) | July, August, September, October | Live SST → |
| Millard Beach | Illinois | James Bay | 20.1°C(68.2°F) | July, August, September, October | Live SST → |
| Miller Place Beach | New York | James Bay | 21.4°C(70.5°F) | June, July, August, September | Live SST → |
| Millway Beach | Massachusetts | James Bay | 19.6°C(67.3°F) | June, July, August, September | Live SST → |
| Mino-kwe jiigibiik | Michigan | James Bay | 15°C(59°F) | July, August, September, October | Live SST → |
| Miramar Beach | California | Gulf of California | 14.9°C(58.8°F) | July, August, September, October | Live SST → |
| Misquamicut Fire District Beach | Rhode Island | James Bay | 19.7°C(67.5°F) | July, August, September, October | Live SST → |
| Misquamicut State Beach | Rhode Island | James Bay | 19.7°C(67.5°F) | July, August, September, October | Live SST → |
| Mitchell Bluff | Maryland | Coastal Waters | 24.1°C(75.4°F) | July, August, September | Live SST → |
| Mokapu Beach | Hawaii | Coastal Waters | 26.8°C(80.2°F) | January, February, March, April, May, June, July, August, September, October, November, December | Live SST → |
| Mokolii View Point | Hawaii | Coastal Waters | 26.7°C(80.1°F) | January, February, March, April, May, June, July, August, September, October, November, December | Live SST → |
| Moku‘Auia Beach | Hawaii | Coastal Waters | 26.7°C(80.1°F) | January, February, March, April, May, June, July, August, September, October, November, December | Live SST → |
| Momauguin Beach | Connecticut | James Bay | 22.1°C(71.8°F) | July, August, September | Live SST → |
| Monastery Beach | California | Gulf of California | 14.9°C(58.8°F) | August, September, October, November | Live SST → |
| Money Beach | Connecticut | James Bay | 22.3°C(72.1°F) | July, August, September | Live SST → |
| Monhegan Bluffs Beach | United States | James Bay | 19.9°C(67.8°F) | July, August, September, October | Live SST → |
| Monroe Landing | Washington | Coastal Waters | 11.4°C(52.5°F) | June, July, August, September | Live SST → |
| Monterey State Beach | California | Gulf of California | 14.9°C(58.8°F) | August, September, October, November | Live SST → |
| Monterey State Beach | California | Gulf of California | 14.9°C(58.8°F) | August, September, October, November | Live SST → |
| Montrose Beach | Illinois | James Bay | 20.2°C(68.4°F) | July, August, September, October | Live SST → |
| Monument Beach | Massachusetts | James Bay | 20.2°C(68.4°F) | June, July, August, September | Live SST → |
| Moody Beach | Maine | James Bay | 16.5°C(61.7°F) | June, July, August, September | Live SST → |
| Moonstone Beach | California | Gulf of California | 20.8°C(69.4°F) | July, August, September, October | Live SST → |
| Moran Lake Beach | California | Gulf of California | 14.9°C(58.8°F) | August, September, October, November | Live SST → |
| Morningside Beach | Connecticut | James Bay | 22.3°C(72.1°F) | July, August, September | Live SST → |
| Morro Rock Beach | California | Gulf of California | 15.4°C(59.7°F) | August, September, October, November | Live SST → |
| Morro Strand State Beach | California | Gulf of California | 15.4°C(59.7°F) | August, September, October, November | Live SST → |
| Moss Beach | California | Gulf of California | 14.9°C(58.8°F) | August, September, October, November | Live SST → |
| Mother's Beach | California | Gulf of California | 20.3°C(68.5°F) | July, August, September, October | Live SST → |
| Mothers Beach | Maine | James Bay | 16.5°C(61.7°F) | June, July, August, September | Live SST → |
| Muir Beach | California | Coastal Waters | 14.5°C(58.1°F) | July, August, September, October | Live SST → |
| Munson Beach | Illinois | James Bay | 20.3°C(68.5°F) | June, July, August, September | Live SST → |
| Myrtle Beach | South Carolina | Atlantic Ocean | 27.1°C(80.8°F) | Jun, Jul, Aug, Sep | Live SST → |
| Myrtle Island Beach | United States | Coastal Waters | 24.4°C(75.9°F) | July, August, September | Live SST → |
| Nahant Beach | Massachusetts | James Bay | 17.6°C(63.7°F) | June, July, August, September | Live SST → |
| Nākeikiapua | Hawaii | Coastal Waters | 26.7°C(80.1°F) | January, February, March, April, May, June, July, August, September, October, November, December | Live SST → |
| Nanny Goat Beach | Georgia | Gulf of Mexico | 28.2°C(82.8°F) | June, July, August, September, October | Live SST → |
| Napeague Beach | New York | James Bay | 20.5°C(68.9°F) | July, August, September, October | Live SST → |
| Naples | Florida | Gulf of Mexico | 30°C(86°F) | Apr, May, Jun, Jul, Aug, Sep, Oct, Nov | Live SST → |
| Naples Beach | California | Gulf of California | 14.9°C(58.8°F) | July, August, September, October | Live SST → |
| Narragansett Town Beach | Rhode Island | James Bay | 19.6°C(67.3°F) | July, August, September, October | Live SST → |
| Narrow Place Beach | Maine | James Bay | 14.1°C(57.4°F) | July, August, September, October | Live SST → |
| Nauset Beach | Massachusetts | James Bay | 18.3°C(64.9°F) | June, July, August, September | Live SST → |
| Nauset Light Beach | Massachusetts | James Bay | 18.3°C(64.9°F) | June, July, August, September | Live SST → |
| Nauyaug Coast | Connecticut | James Bay | 19.7°C(67.5°F) | July, August, September, October | Live SST → |
| Navesink Beach | New Jersey | Coastal Waters | 21.9°C(71.4°F) | June, July, August, September | Live SST → |
| Neals Beach | Virginia | Coastal Waters | 24.9°C(76.8°F) | July, August, September | Live SST → |
| Needle Rock Beach | California | Coastal Waters | 12.5°C(54.5°F) | August, September, October, November | Live SST → |
| Nejecho Beach | New Jersey | Coastal Waters | 21.9°C(71.4°F) | June, July, August, September | Live SST → |