The Big Island runs two weather calendars at once, so the right month depends on which coast you will be standing on. The Hilo side averages 120 to 127 inches of rain a year and has no dry month. The leeward shoreline gauges near Kailua Kona and Kawaihae average under ten. Whales, swell and hurricane season each have their own window. Here is what the year actually looks like, coast by coast.
There is no single best month, because the island does not have one season. It has a windward season and a leeward season running at the same time. On the east side, Hilo's driest month is June at about 7.4 inches and its wettest is November at about 15.5 inches, out of an annual total of roughly 120 to 127 inches depending on the gauge. On the leeward shoreline, the 1991-2020 normals for the Kailua Kona gauge and the Puʻukoholā Heiau gauge near Kawaihae are 9.9 and 9.0 inches for the entire year.
So pick by what you came for. Humpback whales are in Hawaiian waters November through April. North Pacific swell lands on the north and west facing shores in the state's winter season, November through April. Southern Hemisphere swell reaches the south facing Kaʻū coast in the summer season, May through October. Central Pacific hurricane season runs June 1 to November 30. The month-by-month weather guide breaks the numbers down by side.
Humpback whales are in Hawaiian waters November through April, and the sheltered Kona and Kohala coasts on the west side are the easiest place to look for them from shore.
Winter is also the state's high-surf season for north and west facing shores. Hāpuna, Kaunaʻoa, Kua Bay and Pololū are the beaches that change most. Hilo is wet in these months: about 9.3 inches in January, 9.6 in February and 13.4 in March. Kona is at its driest, with February averaging about 1.6 inches, and December and January are its least cloudy months at under 50 percent cover.
Trade winds are least dependable now, blowing 50 to 80 percent of the time from October through April against 80 to 95 percent from May through September. Snowstorms drop a foot or more on the upper slopes of Mauna Kea and Mauna Loa several times a year on average, almost always between October and May.
The last whales trail off through April. Hilo is still wet in April at about 11.5 inches, then drops to about 8.1 in May. On the Kona side the trend runs the other way: April through June are the cloudiest months of the year there, at roughly 70 percent cloud cover, as the afternoon shower cycle sets in.
One scheduling note for the east side. The Merrie Monarch Festival is a week-long hula festival in Hilo; the 2026 festival ran April 5 to 11 and the 2027 festival is scheduled for March 28 to April 3. If you want to be in Hilo that week, book well ahead.
Summer flips the Kona coast. Unlike the rest of the state, the leeward Kona side is wetter in summer than in winter: at Nāpoʻopoʻo the average monthly rainfall is 2.80 inches in winter against 3.70 in summer. In Kailua-Kona the wettest months are July and September at about 2.9 inches each, which is still less than Hilo's driest month.
Mornings are the usable part on that coast. Kona skies are clearest from 8 to 10 a.m. and reach roughly 80 percent cloud cover by 2 p.m. Meanwhile Hilo has its driest month in June at about 7.4 inches, then climbs back to about 10.8 in July.
The south facing Kaʻū coast, including Punaluʻu and the Honuʻapo area, gets its surf now: the state lists large swells arriving frequently on south shores in the May through October season. Central Pacific hurricane season runs June 1 to November 30, and NOAA's 2026 outlook gave a 70 percent chance of an above-normal season with 5 to 13 tropical cyclones. That is a seasonal probability, not a forecast of anything hitting the island.
October still reads like summer on the east side, with Hilo highs near 83°F and about 9.8 inches of rain. The exception on the west side is Ironman week. The 2026 Ironman World Championship returns to Kailua-Kona with the men's and women's races on the same day, scheduled for Saturday, October 10. The town is busy for days around it.
November is the wettest month in Hilo, averaging about 15.5 inches. On the leeward side it is one of the two driest months at about 1.7 inches. November is also when humpback whales start arriving in Hawaiian waters.
Kīlauea has been intermittently active within Halemaʻumaʻu crater at the summit since December 23, 2024, in lava fountaining episodes that have mostly continued for a day or less. Whether you see lava is not a matter of picking the right month. Check the USGS Hawaiian Volcano Observatory updates a day or two before you go, and check the park's own alerts.
Vog is the other one. It is the hazy air pollution caused by volcanic emissions from Kīlauea, and under trade winds the far downwind area is primarily the west side of Hawaiʻi Island, while communities closer to the vents, from Ocean View to Hilo, get both sulfur dioxide gas and fine particles. The park warns that hazardous volcanic gases can be a danger to sensitive groups and tells visitors to check air quality frequently during a visit.
Hawaiʻi Volcanoes National Park is open 24 hours a day, 7 days a week, including holidays, though the Kahuku Unit is open only Thursday through Sunday, 8 a.m. to 4 p.m. Entry is $30 per vehicle for seven days, $25 per motorcycle, $15 per person on foot or bike, and the park does not accept cash. Remaining 2026 fee-free days are August 25, September 17, October 27 and November 11. Expect closures and delays from a two-year construction project repairing damaged buildings and infrastructure at the summit.
Match the month to the coast you care about. Whales and north-shore surf mean November through April on the Kohala and Kona side. South swell on the Kaʻū coast means May through October. If Hilo, Puna and the volcano are the trip, June is the driest month over there at about 7.4 inches and November is the wettest at about 15.5.
Then check the day itself rather than the season. Conditions on this island change by coast and by hour. Start with today's beach conditions and the surf-season guide so you are on the coast that is out of season for swell.