Dry weather in the weeks before summer has helped spread wildfires over thousands of acres and threatened neighborhoods from Waianae to Kailua.

Fire departments and law enforcement leaders from city, state and federal agencies gathered Wednesday to urge the public to be careful and vigilant.

Capt. Terry Seelig, Honolulu Fire Department spokesman, said the agencies wanted to hold a wildfire season news conference several weeks ago "but we’ve been so busy fighting fires that we couldn’t get this rolled out."

At the end of May, the Honolulu Fire Department had recorded 132 wildfires this year, 43 of them in May alone, compared with 15 in May 2011, a much wetter period than the same 31 days this year. The average for May over the past eight years has been 46.

The tally does not include several fires that recently occurred in West Oahu, including one that began in Lualualei Valley and spread to Waianae Valley. That one burned more than 1,200 acres, and firefighters from several jurisdictions worked several days to bring it under control.

Besides threatening homes, the fires have shut down roads and taxed the resources of several agencies, Seelig said.

This year, so far, has been "a little more active in terms of fire spread," he said. "It’s probably weather-driven."

Last summer was wetter than usual, which was beneficial in keeping wildfires fewer and smaller. But that may also be a reason why fires have tended to be larger and more easily spread this year, Seelig said.

"Fuel — the brushes, the grasses, the trees — had a year of not burning in a lot of areas and now they’re heavier and thicker," he said. "And now that it is getting to the dry season, going back to a more traditional pattern. We’re starting to see the fuels dry out and we’re starting to see the winds pick up. Those are the prime determinants."

U.S. Army Garrison Hawaii Fire Chief Scotty Freeman said moisture content had been on par with last year up until about a month ago.

"Our tradewinds, our warm weather, the lack of rain is dropping our moisture content, which is making our fuels out there a lot more volatile than they have been," he said.

Maj. Richard Robinson, head of the Honolulu police Criminal Investigation Division, said about 38 percent of more than 330 wildfires investigated last year were arson. So far this year, about 38 percent to 40 percent "have an arson element to them," he said.

HFD Chief Kenneth Silva urged the public to report fires and suspicious activity immediately, as well as hazardous conditions that may contribute to wildfires. He also urged people to protect homes by clearing out combustibles, creating firebreaks and cleaning roofs and gutters, and to create an evacuation plan to be used in the event of an emergency.