Average Ocean Temperatures for Hawaii
The water's warm enough to swim in at any time of the year on beaches in Hawaii. The Pacific islands' average ocean temperatures for each month are listed below in degrees Fahrenheit and degrees Celsius.
At Honolulu on Oahu, the ocean stays as warm as a heated swimming pool all year long. Ocean temperatures do differ by a few degrees throughout the Hawaiian Islands, though. The water off Honolulu, for instance, is typically 5 °F (3 °C) warmer than at Hilo on the Big Island.
Yet Hawaii's ocean temperatures don't vary much from month to month. The water fluctuates by only 5 °F over the year off Honolulu. At Hilo, the temperature stays even steadier, varying just 3 °F (2 °C) annually.
The Pacific Ocean at both cities reaches its highest temperature in September and October. By March, Hilo's water has dropped to its coldest of the year, at 71 °F (21.7 °C), on average. The water during winter at Honolulu's beaches typically maintains a steady 76 °F (24 °C) from January through to April.
National Oceanographic Data Center. NODC Coastal Water Temperature Guide (CWTG).