Honolulu in August: Weather, Sea Temperature and How It Compares to July and September

HONOLULU · AUGUST · SOUTH SHORE

Honolulu’s August runs hot and dry at the airport gauge: an average high of 88.8°F, an average low of 75.6°F, and 0.84 inches of rain for the entire month. The sea off the south shore sits at 79.6°F. On August 15 the sun comes up at 6:09 a.m. and goes down at 7:02 p.m., which leaves 12 hours and 53 minutes of daylight to spend on the water.

What the month holds back is the night. The low normal never leaves the mid-70s, so an evening outdoors is warm rather than fresh, and the air conditioning does the cooling. If your dates are still open, the twelve-month view lives in the best time to visit Honolulu, and the month before this one is covered in Honolulu in July.

On this page

• Honolulu weather in August88.8°F days, 0.84 inches of rain
• Can you swim in August?The sea at 79.6°F
• How busy is August, and when to bookCrowds and booking ahead
• Things to do in AugustWaikīkī, Diamond Head, Hanauma Bay
• A two-day planTwo days, hour by hour
• August vs July and SeptemberHow the three months compare
• Is August a good time to visit?The verdict, for whom

Every figure here comes from one instrument: NOAA’s 1991-2020 normals for station USW00022521, at Honolulu International Airport on the leeward south shore. That gauge describes Waikīkī and the airport strip well. It never sees the windward side or the mountains behind town, which take several times the rain. Read 0.84 inches as a south-shore number, not an island one.

Honolulu weather in August: average highs, lows and rain days

The normals below are station normals rather than a grid-cell reanalysis: a real thermometer at the airport, averaged by NOAA NCEI over 1991-2020. August posts an average high of 88.8°F, an average low of 75.6°F, and 0.84 inches of precipitation across the month. Local times here are HST, ten hours behind UTC.

Measurable rain reaches the gauge on 1.2 days in an average August, roughly one day in twenty-five. Under an inch for a whole month is not a rain plan, it is a shower or two that crosses the south shore and moves on. Pack for sun and carry nothing heavier than a thin shell for the afternoon.

Day and night are 13.2°F apart, and the bottom of that range is 75.6°F. Nothing in it asks for a sweater. What it asks for is a second shirt for the afternoon, a hat for the hours either side of noon, and one light layer kept back for over-cooled restaurants and the flight home.

On August 15 sunrise falls at 6:09 a.m. and sunset at 7:02 p.m. HST, 12 hours and 53 minutes apart. The evening is the useful half of that. Dinner at seven still begins in daylight, and anything you plan to climb fits comfortably before the heat if you are moving at first light.

Can you swim in Honolulu in August? Sea temperature on the south shore

The sea off Honolulu averages 79.6°F in August in the Open-Meteo marine record, taken as the mean of daily maxima over 2015-2024. A daily maximum runs a shade warmer than a 24-hour mean, so treat 79.6°F as the top of the day’s range rather than the water you step into at dawn.

Nobody needs neoprene at that temperature, and nobody gasps going in. The water sits 9.2°F below the 88.8°F air, cool enough to feel like relief and warm enough that an hour in it is ordinary. Small children last as long as their parents do, which is the practical difference between a Hawaii beach day and a California one.

No monthly wind or swell series was available, so nothing here ranks August’s surf against other months. Read the lifeguard flags on the day and the National Weather Service Honolulu forecast before a long swim, and take 79.6°F for what it is: one stretch of water off one side of one island.

How busy is Honolulu in August? Waikīkī crowds and school holidays

August falls at the tail of the mainland school summer break, and that is a calendar fact rather than a price signal. We found no occupancy series and no monthly hotel rate curve, so we call no month the cheapest or the dearest. Anyone quoting you a twelve-month price curve for Waikīkī should be able to say where it came from.

Fix the flight and the room first, and put anything with timed entry on the list the same day. Diamond Head and Hanauma Bay each publish their own entry and reservation rules, and we could not verify their current fees or booking windows before publication. Read both operators’ pages the week you lock your dates, not the week you land.

Whatever lodging tax lines appear on a Honolulu hotel bill, we could not verify their current rates in time, so no percentage goes in this paragraph. Ask the property for the all-in nightly total with taxes and any resort or parking fee included, rather than the headline rate. Over seven August nights that gap is the size of a day’s car rental.

If one line of the budget moves the month, make it the distance between your bed and the water. With afternoons at 88.8°F and a sea 9.2°F cooler, a room you can walk back to at two o’clock buys you the second half of every day. A car left in a lot all week buys you nothing before dinner.

Things to do in Honolulu in August: Waikīkī, Diamond Head and Hanauma Bay

Of July, August and September, August carries the fewest days of measurable rain (1.2) and the highest afternoon normal (88.8°F). That combination is what the month hands you: water days with the lowest odds, among the three, of losing an afternoon to weather. It is a swimming month with a climb attached, not a hiking month with a beach attached.

Waikīkī Beach is the default and works with no car at all. Diamond Head State Monument holds the crater trail above it. Hanauma Bay Nature Preserve sits east along the coast for snorkeling, Ala Moana Regional Park gives a calmer swim with its own parking, and Pearl Harbor National Memorial is the half day inland. Fees, hours and reservation rules come from each operator, and we did not verify current figures.

The water barely shifts across the season: 79.3°F in July, 79.6°F in August, 80.5°F in September on the marine record. The air moves more, and the 9.2°F gap between an 88.8°F afternoon and 79.6°F water is what sets the order of a day. Climb the crater at first light, snorkel through the middle of the day, keep an indoor hour for the two after lunch.

No August event dates could be verified, so none are listed, and no free-admission day is claimed. What costs nothing in August costs nothing all year: the sand at Waikīkī, the shoreline walk toward Ala Moana, and a 7:02 p.m. sunset that lands late enough to follow a full day in the water.

Honolulu in August: a two-day itinerary

Day one starts at the 6:09 a.m. sunrise and goes straight up Diamond Head, back down before nine while the air is still short of its 88.8°F normal. Late morning belongs to Waikīkī, lunch to somewhere with a roof, and the flat part of the afternoon to 79.6°F water rather than to the sand beside it. Shower, eat early, walk out for the 7:02 sunset.

Day two takes Pearl Harbor first thing and the coast from lunch onward, with the swim at Hanauma Bay or Ala Moana and dinner while the light holds. If the sky turns, keep the scale in mind: 1.2 measurable-rain days and 0.84 inches for the whole month. Wait it out at the Bishop Museum or the Honolulu Museum of Art, hours checked the night before, then go back out.

Honolulu in August vs July and September

Across the three months the air barely argues: 88.1°F in July, 88.8°F in August, 88.4°F in September on the same NOAA normals. Rain separates them. July takes 0.52 inches over 1.3 days of measurable rain, August 0.84 inches over 1.2 days, September 0.88 inches over 2.2 days. The marine record puts the sea at 79.3°F, 79.6°F and 80.5°F in that order.

Shift four weeks forward and you gain 0.9°F of water and 0.8°F off the night low, and you pay one extra day of measurable rain. Shift four weeks back and July gives you the driest of the three at 0.52 inches, with water 0.3°F cooler and nights 0.5°F cooler. Nobody feels a third of a degree in the sea. The rain-day count is the only gap on that table you would notice from a beach towel.

Is August a good time to visit Honolulu?

Yes, if the trip is built around water and daylight. August delivers the highest afternoon normal of the three months at 88.8°F, the fewest measurable-rain days at 1.2, a sea at 79.6°F and 12 hours 53 minutes of light in mid-month. No, if you want a cool evening, because the low normal holds at 75.6°F, or if your dates are flexible and school holidays are not your constraint.

Move to September when warmer water is the point: 80.5°F on the marine record, with nights 0.8°F cooler. The cost is 2.2 days of measurable rain against August’s 1.2, and 0.88 inches instead of 0.84. Move back to July when dry is the point, since 0.52 inches is the driest of the three, and accept water at 79.3°F.

Neither neighbor puts 88.8°F afternoons together with just 1.2 days of measurable rain over water already at 79.6°F.

The last word

Book August for the water rather than for the forecast. The figure that really decides the month is not the 0.84 inches of total rain but the 0.2 days an average August records an inch or more, which works out to one August in five with a single soaking day and four with none. Climb at 6:09, swim through the middle of the day, and keep one indoor afternoon in reserve that you will probably never use.

Sources & data for this guide

• August normals (88.8°F / 75.6°F / 0.84 in) · NOAA NCEI monthly normals 1991-2020, station USW00022521, Honolulu International Airport · checked Sep 15, 2026
• Rain-day counts (1.2 days at 0.10 in or more, 0.2 days at 1 in or more) · NOAA NCEI 1991-2020, same station · checked Sep 15, 2026
• Sea surface 79.6°F, mean of daily maxima 2015-2024 · Open-Meteo Marine API · checked Sep 15, 2026
• July and September normals, and their sea figures (79.3°F, 80.5°F) · NOAA NCEI 1991-2020 for air, Open-Meteo Marine 2015-2024 for sea · checked Sep 15, 2026
• Sunrise 6:09 a.m. and sunset 7:02 p.m. on August 15 · sunrise-sunset.org, UTC values converted to HST · checked Sep 15, 2026
• Editorial note: the airport gauge sits on the leeward south shore and does not represent windward Oahu. Admission fees, reservation windows and lodging tax rates were not verified for this page, and no August event date could be confirmed, so none is cited · check operators when you book.