"I say El Niño years in the winter are good tourist weather but bad weather for the permanent residents," said Jim Weyman, area manager and meteorologist in charge of the weather service forecast office in Honolulu. "It impacts water supplies, ranching and farming and catchment systems on the Big Island."

The recurring climate phenomenon occurs every few years and yesterday the weather service predicted a weak-to-moderate El Niño from mid-December through March of next year.

El Niño winters hit Hawai'i from 2004 to 2005 and from 2002 to 2003. Both were weak to moderate. The strongest El Niño in recent memory was from 1997 to 1998.

But the current conditions will come at the end of a curious year for weather in Hawai'i, where residents experienced record-breaking rainfall in March and drier than normal conditions in the summer.

The heavy spring rains may have flooded locations across the state but rain gauges recorded below normal levels over the summer and drought conditions developed on upcountry Maui, Moloka'i and in Waimanalo, the weather service said.

The El Niño conditions start with warmer than normal sea surface temperatures at the equatorial Pacific. Just a single degree of added warmth can affect weather patterns around the world.

As the pattern develops in the fall months, it increases the chances of tropical depressions, tropical storms and hurricanes caused by unusually persistent low-level west winds in the tropical central Pacific, the weather service said.

When Hurricane Iwa battered Hawai'i in November 1982, it came at the start of an El Niño year, Weyman said.

As an El Niño matures in Hawai'i in December, it creates dry, cloudless days over the course of the next few months. During the strong El Niño of 1997-98, the Ko'olau Mountains were often cloud free, Weyman said.

"You have slightly warmer days and slightly cooler nights," he said. "Without the cloud cover you heat up more during the day and at night without the cloud cover, you radiate more heat into the atmosphere and it's cooler."

Conditions also will be ripe for extended periods of light to southerly winds — the kind of sticky weather that weather service meteorologist Nezette Rydell yesterday summed up with a single word: "Blech."

"When we have light and variable winds we have those pollutant clogged days," Rydell said. "The trades don't move the exhaust from the cars. If the winds are from the southeast, we get vog mixed in."

How many muggy episodes? Anywhere from two to 12, she said.

The dry El Niño weather can severely affect leeward areas, which count on wet winters, said Kevin Kodama, senior service hydrologist for the Honolulu forecast office.

"For a lot of areas, particularly leeward areas, that's when they would want to get a lot of rain," he said. "When the tap turns off, it makes the impact more significant."

Crop failure is possible for areas without another source of irrigation water. Livestock suffers, too. And out-of-season wildfires are a possibility, he said.

If there's an up side to an El Niño, it's the surf. It produces powerful storms northwest of Hawai'i. The weather service said there could be 20 additional swells where wave faces can reach 15 feet to 25 feet.

Meteorologist aren't expecting this winter's waves to match those of the 1997-98 El Niño, when the swell trains came one after the other and Jan. 28, 1998 — Big Wednesday — was cemented into surfing legend.

That's the day surfer Ken Bradshaw caught the biggest wave ever ridden on O'ahu's north shore. Its giant blue face was as tall as an eight-story building. Onlookers from the hillsides of Pupukea that day — according to Honolulu Advertiser archives — estimated the wave to be at least 45 feet with a face 80 feet high.

Reach Mike Gordon at mgordon@honoluluadvertiser.com.