Photo by Jairo Gonzalez on UnsplashHonolulu in September averages a high of 29.9°C (86°F) and a low of 23.1°C (74°F), with about 21.9 mm of rain spread across 7 days. That is a narrow temperature band and very little rain, so the three things that actually decide your comfort are sun protection, breathable fabrics that dry fast, and one warm layer for elevation and air conditioning. Nothing else on your list will matter as much as those three.
What the weather is actually like in September
The gap between the average high and the average low is under 7°C. That is the defining fact of a September trip. You will not experience the day-to-night temperature swing that drives packing decisions in most destinations. A shirt that works at 2pm still works at 9pm on a Waikiki sidewalk. This is why layering advice written for mainland travel does not transfer here.
The rain figure deserves a closer look. 21.9 mm across 7 days averages roughly 3 mm per rainy day — that is a passing shower, not a rain event. Hawaiian rain in September tends to arrive, soak the pavement, and clear within the time it takes to finish a coffee. Seven rainy days out of thirty also means you should expect rain on roughly one day in four, but "a rainy day" in these numbers rarely means a day you cannot go outside.
September is the tail end of the dry season and the peak of Pacific hurricane season, which runs June through November. Direct hurricane landfall on the islands is rare, but tropical systems passing to the south can bring several days of humidity, heavy surf, and shifting winds. This is worth watching in the week before you fly, not worth packing for.
The other September-specific factor is ocean temperature. Water around the islands is at or near its annual peak in late summer, typically the warmest water of the year. Combined with air in the mid-80s, this changes what you pack for the water more than what you pack for land.
What to wear — by layer
Base layer / everyday clothes. Linen, cotton-linen blends, rayon, and technical synthetics. Avoid heavy cotton t-shirts as your only option — at 86°F with high humidity, thick cotton absorbs sweat and stays wet against your skin for hours. Two or three lightweight button-down shirts will outperform five heavy tees. Plan on shorts and lightweight pants; you will wear shorts most of the trip.
Sun layer. This is the layer people skip and regret. Hawaii sits at roughly 21°N latitude, and the September sun is still high in the sky. A long-sleeve UPF shirt (rash guard style) does more work than any amount of sunscreen reapplication, especially for snorkelling, where your back is exposed and horizontal to the sun for an hour at a time. A wide-brim hat beats a baseball cap because it covers your ears and neck.
Warm layer. You need exactly one, and the reason is elevation, not season. If you are going up Haleakalā on Maui (10,023 ft) or Mauna Kea on the Big Island (13,803 ft) for sunrise or stargazing, temperatures at the summit can sit near or below freezing regardless of the month. The 86°F figure is a sea-level number. Haleakalā sunrise also requires a reservation booked in advance — check that before you pack for it. If you are staying on Oʻahu and not going to altitude, a light fleece or hoodie is enough, and its main job will be surviving over-air-conditioned restaurants, buses, and the flight itself.
Rain layer. A packable windbreaker or light shell, not a rain jacket. With 3 mm of rain on a typical wet day, you want something that handles a ten-minute shower and stuffs into a daypack. A waterproof hardshell is overkill and will make you miserably hot the moment the rain stops.
Feet. Sandals for most of the trip, plus one closed-toe option. Lava rock and dried lava fields cut sandals and feet, and many trails — including the popular ones on Kauaʻi and the Big Island — are wet, red, and slick. Water shoes matter more than hiking boots for most visitors; heavy boots are almost always a mistake unless you have a multi-day backcountry plan.
What most people get wrong for September specifically
Packing for the swing that never comes. The 74°F low is not cold. Travelers see "low 74" and pack sweaters, jeans, and evening layers for a temperature that is warmer than a summer afternoon in most of Europe. You will carry them unworn.
Underestimating humidity. September retains summer humidity. Clothes take longer to dry, and anything you rinse in a hotel sink overnight may still be damp in the morning. This argues for synthetics and linen over cotton, and for packing one more shirt than you think you need rather than planning to wash.
Bringing the wrong sunscreen. Hawaii law prohibits the sale of sunscreens containing oxybenzone and octinoxate. If you bring a bottle from home, check the label; if it contains either, you may not be able to use it responsibly on reefs and will need to buy a mineral (zinc oxide or titanium dioxide) replacement locally at resort prices. Buy mineral sunscreen before you fly.
Assuming beaches are calm because it is not winter. North Shore surf is at its lowest in summer, but late-summer swells from distant storms can appear with little visible warning. If you are relying on a specific beach for swimming, check conditions the day of rather than assuming September is safe by default.
Treating all islands as one climate. Hilo on the Big Island is one of the wettest cities in the United States; Kona on the same island's leeward side is dry. The 21.9 mm Honolulu figure describes Oʻahu's south shore. If your trip includes Hilo, Hana on Maui, or the north side of Kauaʻi, expect meaningfully more rain and pack the shell layer with more conviction.
What you can skip
- Jeans. Heavy, slow to dry, and hot at 86°F. If you want long pants for dinner, bring lightweight chinos or linen trousers.
- A heavy rain jacket. Covered above — the rainfall total does not justify it.
- Formal clothes. Hawaii's dress code is genuinely relaxed. An aloha shirt with a collar clears the bar at nearly every restaurant on the islands.
- A hair dryer. Essentially every hotel provides one, and the humidity will undo its work anyway.
- Beach towels. Hotels and rental condos supply them, and they eat luggage volume faster than anything else you could pack.
- Snorkel gear, unless you own a mask you love. Rentals are widely available and cheap. A personal mask is worth carrying if fit has been a problem for you; fins and a snorkel are not.
- Multiple pairs of shoes. Sandals plus one closed-toe pair covers everything most visitors do.
- A thick sweater or coat. One light fleece covers both air conditioning and, layered with your rain shell, a summit sunrise.
September Hawaii packing checklist
- 2–3 lightweight button-downs or linen shirts
- 3–4 quick-dry t-shirts or tanks
- 2–3 pairs of shorts
- 1 pair lightweight long pants (linen or chino)
- 1 long-sleeve UPF sun shirt / rash guard
- 2 swimsuits (one dries while you wear the other)
- 1 light fleece or hoodie
- 1 packable windbreaker or light shell
- Wide-brim hat
- Sunglasses with UV protection
- Reef-safe mineral sunscreen (zinc oxide or titanium dioxide), SPF 30+
- After-sun lotion or aloe
- Sandals or flip-flops
- Closed-toe shoes (trail runners or water shoes)
- Insect repellent — mosquitoes are active in wet, shaded areas year-round
- Dry bag or waterproof phone pouch
- Reusable water bottle
- Daypack
- Any prescription medication in original packaging
- Warm layer, gloves, and beanie only if Haleakalā or Mauna Kea summit is on your itinerary
Frequently Asked Questions
Is September a good time to visit Hawaii?
For weather, yes. September has some of the year's most stable conditions — 29.9°C highs, 23.1°C lows, and only 21.9 mm of rain in Honolulu across the month. The caveat is hurricane season, which runs through November. Direct impacts are uncommon but not impossible, and travel insurance is a more reasonable purchase in September than in, say, April. September is also a shoulder month after the summer family rush and before the winter surf and holiday season, which usually means lower crowds and better rates.
Do I need a jacket in Hawaii in September?
At sea level, no — not for warmth. Bring one light fleece and one packable shell, and expect to use them for air conditioning, early-morning boat trips, and short showers rather than for cold. The exception is altitude: Haleakalā and Mauna Kea summits can approach freezing at sunrise in any month, and if either is on your plan you need a real warm layer, plus gloves and a hat.
How much rain should I expect in September in Hawaii?
In Honolulu, about 21.9 mm total across roughly 7 days — a small amount spread thinly. Most of it falls as brief showers rather than sustained rain, and it often passes within minutes. This figure is specific to Oʻahu's leeward south shore. Windward and northern coasts, and especially the Hilo side of the Big Island, are consistently wetter than this, so adjust upward if your itinerary is not Honolulu-centered.
Build your own list: the TripPack generator checks the live forecast for your exact dates and adds voltage, visa and water-safety notes. See also the Hawaii packing list.