The U.S. Geological Survey raised Kilauea's volcano alert level from Advisory to Watch and its aviation color code from Yellow to Orange after lava began slowly overflowing the north vent inside Halemaumau crater. The Hawaiian Volcano Observatory issued the change at 1:00 p.m. Hawaii Standard Time on Monday, September 7, and placed the start of the overflow at roughly 12:45 p.m. HST the same day.

That overflow is what volcanologists call precursory activity. It is not the main event. The observatory forecasts that lava fountaining episode 55 will begin between September 7 and September 10, and it has committed to issuing a separate aviation notice at the moment fountaining actually starts. As of the most recent notice reviewed for this report, no such notice had been published, and fountaining had not begun.

For residents of the Big Island, the practical change is smaller than the alert language suggests but not zero. All eruptive vents and lava flows remain confined to Halemaumau crater within a closed area of Hawaii Volcanoes National Park, and that has not changed. What has changed is wind direction. The observatory reported light winds from the south with the potential to carry volcanic fumes, and possibly tephra once fountaining begins, northward past the rim of Kaluapele, the summit caldera.

Inside the Precursory Signal the Observatory Is Tracking

The signal driving this forecast is ground tilt. When magma refills the shallow summit reservoir, the ground inflates measurably, and the observatory tracks that recovery on a tiltmeter at Uekahuna, designated UWD.

Episode 54, which ended on the evening of August 25 after about nine hours of fountaining, drained 12.7 microradians of tilt from the summit. Refilling since then has been irregular, interrupted by several deflations of varying size and duration. Rapid inflation resumed around 10 a.m. HST on Saturday, September 5. By Monday morning, tilt had gained more than nine microradians since Saturday, which the observatory reported had returned the summit to the level recorded before episode 54 began.

Then it stalled. In its Monday morning daily update, issued at 8:58 a.m. HST, the observatory noted that tilt had leveled off around 6:30 a.m. and was nearly flat, and said precursory activity would be expected later that day or the next if inflation resumed. Roughly six hours later, the overflow started, and the alert level went up.

The same update recorded moderate to strong glow from the north vent overnight, with weaker periodic glow from the west and south vents tied to gas piston activity. It was the first time glow had been observed from the south vent since episode 54 ended. The observatory read that as a sign magma had risen high in the vent conduits.

Vog and Tephra Are Aimed Toward the North Rim

Direction matters more than volume for most households. In several recent episodes, trade winds pushed the plume southwest over the Kau Desert, and tephra fall stayed largely inside the closed park area, with only trace reports of Pele's hair reaching the Kau district.

The current setup is different. Light and southerly winds push emissions toward the north and northeast rims, where public overlooks sit and where more people gather. Even between episodes, sulfur dioxide output from the summit typically runs between 1,000 and 5,000 tonnes per day, and that gas reacts in the atmosphere to form vog. Emission rates climb during an actual fountaining episode.

Exposure is not evenly distributed. People with asthma, chronic obstructive pulmonary disease or other respiratory conditions, along with older adults, young children and pregnant women, face the greatest risk from vog. Outdoor workers downwind and park visitors at north-side overlooks are next. Households far upwind of the summit may notice nothing at all. The Hawaii Volcanoes National Park website carries current closure and visitor information, and the International Volcanic Health Hazard Network maintains guidance on vog exposure.

The Gap Between Precursor and Fountains Has Varied Widely

This is where the forecast window earns its width, and it is the part most coverage skips.

Precursory activity has preceded every recent fountaining episode, but the lag between the two has been inconsistent. Aviation notices archived by the observatory show the gap ran about four hours before episode 54, which began at 10:30 a.m. HST on August 25 after precursory activity started around 6:16 a.m. Before episode 53, the gap was roughly four and a half hours, and before episode 52 it was closer to nine. It stretched past a day before episode 50 and to more than two days before episode 45 in April.

That spread is the reason the observatory publishes a multi-day window rather than a time. A reader who sees that precursory activity has begun should not assume fountains within the hour, and should equally not assume there is a comfortable margin. The eruption episode timeline maintained by the observatory documents each episode since the eruption began on December 23, 2024.

Several summit monitoring stations also remain offline following earlier storm and power-related outages, which the observatory has disclosed in its updates. That is a real limitation on the data behind the current forecast, though the observatory describes its network as mostly recovered.

Guidance for Residents, Visitors and Air Travelers

The observatory's own framing is the useful one. It states that low-level precursory activity "can continue for hours to days" before the lava fountaining episode begins.

Practical steps are modest. Residents downwind can check air quality before outdoor exercise and keep respiratory medication accessible. Visitors planning a trip to the summit should confirm closures with the park before driving, because viewing areas can change on short notice. Aviation color code Orange is a signal to pilots and dispatchers rather than to the general public, but travelers with flights routing near the island may want to monitor carrier advisories, since past episodes have sent plumes to roughly 17,000 feet above sea level and higher.

Nobody should attempt to reach a closed viewing area. The caldera rim around Halemaumau has been closed to the public since late 2007 because of wall instability, ground cracking and rockfalls, and tephra on the crater rim is prone to cracking and slumping that can expose hot and molten material. Residents should follow instructions from the Hawaii County Civil Defense Agency, which the observatory says it is in contact with, and from park officials.

Developing Story Timeline

September 7, 1:00 p.m. HST: The observatory issues a volcanic activity notice raising Kilauea to Watch and Orange after a sluggish overflow from the north vent beginning around 12:45 p.m. HST. Fountaining is forecast for September 7 through 10.

September 7, 8:58 a.m. HST: The morning daily update reports summit tilt has recovered the amount lost during episode 54 but has stalled since about 6:30 a.m., with glow observed overnight from the north, west, and south vents.

September 5, about 10:00 a.m. HST: Rapid summit inflation begins after several days of stop-start deflation.

August 25, 7:33 p.m. HST: Episode 54 ends after about nine hours of continuous fountaining, with maximum north vent fountain heights near 500 feet and a plume to roughly 17,000 feet above sea level.

The next scheduled information is the observatory's daily update, with an unscheduled aviation notice due whenever fountaining begins. Current status is posted on the Kilauea volcano updates page, and definitions for each tier appear in the USGS alert level system reference. What remains unknown is straightforward: whether inflation resumes, whether fountaining begins inside the forecast window or slips past it, which vents participate, and how high fountains reach.

What Readers Want to Know

What actually changed at Kilauea? The U.S. Geological Survey raised the volcano alert level from Advisory to Watch and the aviation color code from Yellow to Orange after lava began overflowing the north vent inside Halemaumau crater on Monday afternoon, Hawaii Standard Time.

Does Watch mean an eruption is happening right now? Lava is erupting at a low level, but the lava fountaining episode had not begun as of the most recent notice reviewed. Watch indicates escalating unrest with increased potential for a hazardous event, or a confirmed eruption with limited hazards.

Which areas could see volcanic haze or ash? Light south winds were pushing emissions toward the north and northeast rims of the summit caldera. That direction differs from recent episodes, which sent material southwest over the Kau Desert.

Who faces the greatest health risk from vog? People with asthma, chronic obstructive pulmonary disease or other respiratory conditions, older adults, young children, pregnant women and outdoor workers downwind of the summit.

Is any community being evacuated? No. All vents and lava flows remain confined to a closed area of Hawaii Volcanoes National Park, and no evacuation orders have been issued.

When will the next update be released? The Hawaiian Volcano Observatory issues daily updates for Kilauea and has said it will publish a separate aviation notice as soon as effusive episode 55 begins.

Should travelers change flight plans? Aviation color code Orange is directed at pilots and dispatchers, not passengers. Travelers routing near the island can monitor carrier advisories, since past episodes have lofted plumes to about 17,000 feet and higher.