On May 2, residents in Leilani Estates noticed cracks in the roads:
This was a warning sign… but of what?
Following the April 30 collapse of Pu’u O’o, a swarm of earthquakes indicated that its magma was slowly moving downrift towards inhabited areas 11 miles away in the Puna District. The HVO had issued a “volcano activity notice” on May 1, warning that lava might break out along the Lower East Rift Zone. They issued further alerts indicating magma was moving underground into Puna District and under Highway 130.
Acting on their information, Civil Defense officials began planning for an eruption and warned lower Puna residents on May 2 to prepare to evacuate, since “Should an eruption occur, residents along the East Rift Zone may have little warning.”
The caption on the USGS website for the above May 2 photo is revealing:
“Puna residents reported to HVO geologists the recent appearance of ground cracks on a couple of roads in and around Leilani Estates. No steaming or heat were observed to originate from the cracks, and the cracks are currently still small (no more than several inches across). These cracks result from deformation of the ground surface due to the underlying intrusion of magma. Earthquake activity remains elevated in this area due to the ongoing intrusion.”
USGS scientists expected heat and steam in advance of lava rising towards the surface, based on past incidents like the 1955 Puna eruption, which also had earthquakes ramp up dramatically before lava outbreaks. So, although scientists had started warning Lower Puna residents on May 1, 2018 to get ready for an eruption, they were still looking for signals of exactly where the lava was going to break out until the day it actually did.
That said, there were news articles from most major news outlets (here’s an example from the San Francisco Chronicle) on May 2 and early May 3 saying the mayor’s office (here’s its May 2 notice) and civil defense were preparing for an eruption in the East Rift Zone/lower Puna area, and that residents should get ready to evacuate at a moment’s notice.