A passing thunderstorm lit up O'ahu skies last night, dumping heavy rain over most of the island and causing minor flooding that forced the closure of several streets, including a portion of Kalakaua Avenue in Waikiki.

For nearly a half-hour last night, the island of Lana'i was under a tornado warning as a thunderstorm capable of producing a twister bore down on the island. The warning was in effect until 10 p.m. and fire officials in Lana'i City reported heavy rain at about 10:30, but no funnel clouds.

National Weather Service forecaster Norman Hui said computer radar showed a tornado was in the area.

"The radar showed a signature of a tornado," Hui said. "There's a certain pattern on the radar that points to the existence of a tornado. It's usually pretty accurate."

The last time a tornado warning was issued for Hawai'i was in January 2004 after a tornado touched down in Central O'ahu. There were no reports of damage or injuries in that incident.

"It's a little uncommon, but it does happen," Hui said of the warning. "It's not one of those things that we issue every day, compared to flash flooding."

The heavy rains caused minor flooding in Waikiki and along the south coast to portions of East Honolulu, including Kapahulu and 'Aina Haina. The Honolulu Fire Department responded to several flooding calls, but there were no reports of major damage, Capt. Kenison Tejada said.

A portion of Kalakaua Avenue was closed about 8:30 p.m. Police routed traffic onto Kuhio Avenue. There were reports of water entering some shops.

The state remains under a flash flood watch at least through tonight, Hui said. The forecast for this weekend is for scattered showers, he said.

"Right now we are not mentioning anything heavy, subject to change," Hui said last night. "Essentially the atmosphere is very unstable. We have a trough west of our area that's drawing all of this unstable, moist tropical air."

The question is: when will all this wet weather end?

"I hope it will end today," Hui said. "Unfortunately such is not the case."

The Kawailoa rain gauge on the North Shore recorded 3 inches of rain in the 24-hour period ending at 8 last night. Other areas with significant rainfall during that period were Wai'anae (2.70 inches), Wheeler Army Airfield (2.58 inches) and Maunawili (1.90 inches).

Reach Curtis Lum at culum@honoluluadvertiser.com.