North Shore Oahu Weather by Month: Rain, Water and Surf

NOAA has no 1991 to 2020 normals for Haleiwa or Waialua town, so this guide uses two nearby stations: Kii-Kahuku, on the coast at the Kahuku end, and Waimea Valley. Figures are average daily highs and lows in °F (NOAA NCEI, pulled October 14, 2026).

Temperatures barely move. At Kahuku the average high runs from 76.5°F in February to 83.1°F in September. Waimea Valley swings wider, from 78.1°F to 86.4°F, and has the coolest nights, 62.2°F in February. NWS Honolulu says Hawaii’s warmest months are August and September and its coolest February and March (NWS).

Rain is where the stations differ. Kahuku averages 32.61 inches a year and Waimea Valley 52.02, against 20.65 in Waikīkī. A third station, the Poamoho Experimental Farm, sits inland, south of Haleiwa and Waialua at 220 feet, and logs 32.99. A rain day has at least 0.10 inch.

Winter is the wetter half. October through March brings 64% of Kahuku’s yearly rain (20.98 of 32.61 inches) and 58% of Waimea Valley’s, against 75% in Waikīkī. November is the wettest month at both coastal and valley stations, with 4.05 and 6.09 inches. Inland Poamoho is the most seasonal at 72%, with 1.09 to 1.79 inches a month from May through September, while Waimea Valley has 8.3 to 12.1 rain days every month.

Averages hide the storms. NWS Honolulu says relatively dry areas “may receive, within a day or a few hours, totals exceeding half of their average annual rainfall” (NWS). Our rainy day guide covers flood alerts.

Haleiwa and Waialua have no NOAA normals station of their own, so we do not print a Haleiwa figure. Use Kahuku for the coast, Waimea Valley for the valley and Poamoho for inland, then check the day. NWS Honolulu has a forecast box where you can enter Haleiwa, HI or Waialua, HI, and its surf zone forecast lists tide times for Haleiwa.

For the water we use NOAA buoy 51201, listed as Waimea Bay: a Waverider buoy owned by PacIOOS in 200 meters of water. We averaged its readings from 2015 through 2025 by calendar month (NDBC historical files; our own analysis of about 165,000 readings, with gaps in some years). Wave height is significant wave height.

The water is coolest in February and March, at 75.5°F on average, and warmest in September at 80.3°F. NWS Honolulu puts the seasonal range near Hawaii at about 6 degrees, from 73 or 74 in late February and March to near 80 in late September or early October (NWS). The buoy’s extremes were 70.0°F in March and 85.3°F in September.

Waves are the bigger swing. The average runs 7.9 feet in January against 3.5 in August, and the highest reading was 29.8 feet, in February. NDBC defines significant wave height as the average of the highest one-third of waves (NDBC), measured in open water, so it is not the surf at a beach. NWS surf forecasts use full face height, trough to crest (NWS).

Hawaii Ocean Safety describes Waimea Bay as often calm and clear in summer and, in winter, “consistently pummeled by high surf and powerful shorebreak.” It lists summer as May through October, with north shores “flat-to-small,” and winter as November through April, with “consistent huge and dangerous swells” on north shores. It says inexperienced surfers, and swimmers of any skill level, should avoid the water in high surf (Hawaii Ocean Safety). NWS Honolulu counts winter as October through April.

The same applies to the snorkel coves. The state’s Pupukea Marine Life Conservation District page says that from about May through October the water is generally calm, but surges are possible, and that in winter months conditions “become extremely dangerous in all areas” of the district (DLNR). Small waves hurt people too: the state says the average wave height when a spinal cord injury occurs is 3 feet (Hawaii Ocean Safety).

Wave conditions are localized, so check the beach you plan to use, on the day.

• Read the NWS surf zone forecast. The forecast gives Oahu surf in feet by shore. Find the north-facing row, and remember the numbers are full face height.
• Know the alert levels. NWS issues a High Surf Advisory for north-facing shores at 15 feet and a Warning at 25 feet (NWS criteria).
• Look at the buoy. The NDBC page for buoy 51201 shows the latest wave height, period and water temperature.
• Ask the lifeguard and read the signs. Our guide to whether it is safe to swim on Oahu today covers the flags and signs.
• Contests are a winter event. Surf contests run in the winter season; the World Surf League posts current dates.

NWS Honolulu says the high behind the northeasterly trade winds is “stronger and more persistent in summer than in winter.” In winter the trades “may be interrupted for days or weeks” by fronts and Kona storms (NWS). In summer, the State adds, northeast trade winds can raise surf on north and east facing shores.

NOAA says humpback whales are generally seen in Hawaii from November through April, with the peak from January through March (NOAA sanctuary). Our North Shore guide and what to do on the North Shore cover the rest, and the Oahu in November guide covers the month the season turns.

• A light rain layer. Kahuku has 4.2 to 7.6 rain days a month and Waimea Valley 8.3 to 12.1.
• One warm layer for winter evenings. Winter lows average 65.7°F at Kahuku in February and 62.2°F in Waimea Valley.
• Sunscreen without oxybenzone or octinoxate. Hawaii bans selling sunscreen with either without a prescription (HRS 342D-21). Check the label on anything you bring.