Water Temperature by Month: Cancún, San Diego, Myrtle Beach & 49 More Beaches

Quick answer: The Caribbean stays warm all year: Cancún, Punta Cana, Aruba and the other island beaches here average 79–82 °F from January to March and 83–86 °F from August to October, above the 70–78 °F NOAA calls comfortable for many swimmers. The Gulf coast swings more: Galveston averages 58 °F in January and 87 °F in August.

How to use it

Pick a beach (the Riviera Maya, the Caribbean islands, the Bahamas, Florida and Texas; Santa Monica to San Diego, Hawaii, Cabo and Puerto Vallarta; the US Gulf coast from Corpus Christi to Destin and the Atlantic from Tybee Island to Cape Cod) and the month you travel; the month you are in is filled in. The answer is the sea’s average that month and where it sits against NOAA’s comfortable range, with most days’ range and the beach’s warmest and coolest months. Below it: the beach’s twelve months as bars, every beach ranked for your month, and, when NOAA has it, the latest day’s reading. Switch to °C if you like.

Where the numbers come from

NOAA’s Optimum Interpolation Sea Surface Temperature (OISST, version 2.1) blends satellite, ship and buoy readings into one daily map on a quarter-degree grid. For each beach the tool takes the nearest grid cell over open water (the beach’s own cell is often land), a few miles offshore, and reads every 4th day from 2006 to 2025: about 150 days for each calendar month, averaged, with the middle 80% as “most days”. It is the sea surface offshore, not the water at your feet. NOAA’s Coastal Water Temperature Guide says “There’s no real optimal temperature, but many people feel “comfortable” swimming in water that is 70° to 78° Fahrenheit”, and warns that “even in the summer, prolonged immersion in water temperatures below 70° Fahrenheit can produce hypothermia.”

In °F, each month’s average from 2006 to 2025. The Mexican Caribbean, the islands and Belize vary by four to six degrees through the year; Holbox, on the Gulf side of the Yucatán, runs cooler, and the Gulf coast beaches of Florida and Texas swing by more than 20 °F between winter and summer.

The other coasts are their own story. Waikiki and Kaanapali barely move, 76–81 °F all year. San Diego stays cool, 59 °F in winter and 71 °F in August, under NOAA’s comfortable range for most of the year. Cabo San Lucas stays in the 70s until June, reaches 80 °F in July and 84 °F from August to October; Puerto Vallarta warms sooner, 80 °F in May and 86–87 °F from July to October. Up the Atlantic coast the swing grows with every mile north: Myrtle Beach goes from 54 °F in February to 83 °F in August, and Virginia Beach from 43 °F to 78 °F.

North of Virginia the sea stays cold into June. Ocean City, Maryland averages 41 °F in February and 76 °F in August; Long Beach Island, New Jersey 40 °F and 75 °F; Cape Cod’s Nantucket Sound side 37 °F and 71 °F, and only July and August reach NOAA’s comfortable range there. Southern California is cooler than San Diego: off Santa Monica the sea never averages 70 °F (69 °F in August and September), and Newport and Huntington Beach reach 70 °F in August only. On the Gulf, Corpus Christi’s Mustang Island goes from 62 °F in February to 85 °F in August and September. A few beaches sit so close that NOAA’s quarter-degree grid gives them one cell, so their numbers are the same and the answer says so: La Jolla and San Diego’s Mission Beach, Newport Beach and Huntington Beach, Orange Beach and Gulf Shores.

Worked examples

Cancún in January. The sea averages 80 °F; most January days 79–81 °F. Its warmest month, September, averages 85 °F.

Punta Cana in March. The coolest month of the year there, and still 80 °F on average, above NOAA’s 70–78 °F comfortable range.

Nassau in February. The sea averages 76 °F, inside NOAA’s comfortable range; by August it is 85 °F.

Galveston in January. The sea averages 58 °F, below the 70 °F under which NOAA warns prolonged immersion can bring on hypothermia; in August it is 87 °F.

San Diego in August. The sea averages 71 °F, its warmest month and just inside NOAA’s comfortable range; in January and February it is 59 °F.

Myrtle Beach in June. The sea averages 79 °F, a degree over the comfortable range; in late spring it is still cooler, 72 °F in May.

Ocean City in July. The sea averages 75 °F, inside NOAA’s comfortable range; in February it is 41 °F, the coldest of the Atlantic beaches here after Long Beach Island and Cape Cod.

Key West in January. The sea averages 73 °F, inside the comfortable range; across the Gulf, Clearwater averages 63 °F.

Common mistakes

• Expecting “warmer” to mean “comfortable”. Above 78 °F the sea is warmer than the range NOAA says many people find comfortable.
• Reading today’s air temperature for the water. In January Galveston’s sea averages 58 °F, whatever the afternoon feels like.
• Treating Florida as the Caribbean. In January the Gulf off Clearwater and Pensacola is below 70 °F; the Keys and Miami stay in the 70s.
• Expecting Southern California to be warm in summer. Santa Monica’s sea never averages 70 °F, and San Diego’s reaches 71 °F in August only.
• Planning on a single day’s reading. Seas move: the middle 80% of days spans a few degrees each month.

Plan the rest of the trip

Read why Caribbean water is so clear and blue, which Caribbean island has the best weather, which side of Florida has warmer water, Punta Cana or Las Terrenas, Antigua or the Bahamas and swimming in the ocean in Key Largo. Before you book the same beaches, check the Sargassum Season Checker for seaweed and the hurricane season for storms; on a Florida beach today, Florida Beach Conditions has the water’s reading at the nearest NOAA station.