Two divers can book the same week in Hawaiʻi and come home with very different trips. One gets flat water and 100-foot visibility at every site. The other spends half the week watching surf from the boat ramp. Much of that is luck, but much of it is knowing how Hawaiʻi's ocean behaves and choosing the coast to match the day. Experienced local divers rarely ask "is it good today?" They ask "where is it good today?"
This page is the diver's version of that local knowledge. It is not a substitute for a briefing from your operator or a lifeguard's advice, both of which are based on what the water is doing right now.
- Surf & advisories
- NWS Honolulu
- Guarded beaches
- Hawaii Beach Safety
- Water quality
- DOH Clean Water Branch
- Box jellyfish dates
- Waikīkī Aquarium calendar
- Tsunami & sirens
- Hawaii EMA
- Emergency
- Call 911
Swell Seasons: Which Coast Works When
The most useful rule for planning dives in Hawaiʻi is that surf is seasonal and directional. From roughly October through April, storms in the North Pacific send long-period swell toward the islands, and north- and northwest-facing coasts take the hit. That is when Oʻahu's North Shore produces its famous big waves and when sites like Shark's Cove, Honolua Bay and Tunnels are usually off the table for divers. During the same months, south-facing coasts are often at their calmest.
In summer the pattern flips. Swell from storms in the Southern Hemisphere reaches south-facing shores, while the north side often goes flat enough to dive. The leeward Kona coast of Hawaiʻi Island sits in the shadow of large volcanoes and is sheltered for much of the year, which is one reason so much Big Island diving happens there.
Trade winds, which blow from the northeast much of the year, add another layer. They put chop on windward coasts and can make channel crossings, such as Maui to Molokini or Lānaʻi, bumpy by late morning. That is why many boats leave early.
| Coast | Typical winter (Oct–Apr) | Typical summer (May–Sep) |
|---|---|---|
| North / northwest-facing | Large surf; many sites closed | Often calm; prime season |
| South-facing | Often calm | South swells possible |
| Leeward (e.g. Kona) | Usually sheltered | Usually sheltered |
| Windward (east) | Trade-wind chop | Trade-wind chop |
These are tendencies, not promises. A winter south swell or a summer north swell can arrive at any time, which is why the daily forecast matters more than the calendar.
Reading the Official Forecast
The National Weather Service forecast office in Honolulu publishes surf forecasts for each shore and issues high surf advisories and warnings when waves reach dangerous levels. If an advisory covers the coast you planned to shore dive, change the plan. Boat operators usually move to a sheltered coast or cancel; take that seriously rather than looking for an operator who will still go.
For lifeguarded beaches, the Hawaii Beach Safety website, set up through the Hawaiʻi Lifeguard Association with the counties, the state Department of Health, the Hawaiʻi Tourism Authority and the University of Hawaiʻi, shows posted hazards such as high surf, strong currents, dangerous shorebreak and jellyfish. Check it the night before and again in the morning.
Currents, Surge and Shore Entries
Rip currents form where water piled up by waves drains back out to sea, often through gaps in the reef or along headlands. Snorkelers and shore divers meet them at the surface, on the way in or out. If you are caught, do not fight straight back toward the beach. Float, signal for help, and once the pull eases swim parallel to shore before heading in. The National Weather Service rip current page explains how to spot them from the beach.
Underwater, surge is the back-and-forth motion that swell creates near the bottom. Even a small surface swell can produce strong surge in shallow water, and it pushes divers into reef and rock. Stay deeper and farther off the structure when surge is present, and never enter an overhead environment such as a lava tube or cavern when the water is moving.
Many Hawaiʻi shore dives start from lava rock. Watch several sets before entering, choose your exit point before you go in, and get through the impact zone quickly between waves with your mask on and regulator in. If the exit looks worse at the end of the dive than it did at the start, it is often safer to swim to a calmer exit than to fight a bad one.
Water Quality After Rain
Heavy rain washes soil, debris and bacteria from streams and storm drains into nearshore water. When this happens the Hawaii Department of Health's Clean Water Branch issues brown-water advisories for affected areas. County ocean safety officials have advised people to stay out of the water during these advisories; reported guidance suggests waiting 48 to 72 hours after the rain stops. Murky water also cuts visibility to near zero, so there is little reason to dive it anyway. Freshwater streams and ponds carry a separate risk of leptospirosis after heavy rain.
Stinging Animals
Box jellyfish are known for arriving near south- and leeward-facing shores about 8 to 10 days after a full moon. Lifeguards post warning signs when they show up, and the Waikīkī Aquarium publishes a calendar of expected dates. Portuguese man-of-war, the blue "bluebottles," tend to blow onto windward beaches when the wind pushes them in. A thin full-length suit or rash guard is the best protection for snorkelers and divers alike. Our marine life guide covers other animals you may meet.
Boat Diving Habits That Matter Here
- Listen to the whole briefing, including entry, exit, current direction and the plan if you surface away from the boat.
- Carry a surface marker buoy and a whistle or other signaling device. Hawaiʻi's blue water makes a lone diver's head hard to spot.
- Watch your gas and your no-decompression limits, especially on deeper wrecks and walls where bottom time runs out quickly.
- Make a safety stop on every dive, and stay well clear of the boat's propellers on ascent.
- Hydrate and avoid alcohol before and between dives.
Altitude, Flying and Recompression
Hawaiʻi's roads climb quickly from the ocean to very high altitude: the summit of Haleakalā on Maui is about 10,000 feet, and Hawaiʻi Island's Saddle Road tops 6,600 feet. Treat a drive up these roads the same way you treat a flight. Divers Alert Network suggests at least 12 hours after a single no-decompression dive and 18 hours after repetitive or multi-day diving before flying, and many dive centers use 24 hours as a simple rule. Our certification guide explains more.
If you or a buddy show signs of decompression illness, call 911, give emergency oxygen if it is available, and tell responders about the dives. The University of Hawaiʻi Hyperbaric Treatment Center at Kuakini Medical Center in Honolulu provides recompression treatment and is designated by Divers Alert Network as a regional coordination center for the Pacific. Dive accident insurance is worth having.
Tsunami Sirens
Hawaiʻi tests its outdoor warning sirens on the first working day of each month at 11:45 a.m., with a steady tone of about a minute. If you hear sirens at any other time, get out of the water, move away from the shore, and follow official alerts from the Hawaii Emergency Management Agency and local broadcasters.
The best dive you can make on a big-surf day is the one you postpone. The reef will still be there tomorrow.