Deadly heat bakes the Midwest and East Coast, floods leave millions homeless in Asia, and a tinder-dry Los Angeles city waits for wildfires.

All of this global weather mayhem and more comes courtesy of La Nina.

A cooling of the ocean surface off the western coast of South America, occurring periodically every 4 to 12 years and affecting Pacific and other weather patterns, which forecasters said Thursday is certain to rebound this winter after showing hopeful signs of weakening during the spring.

For Southern California and the world, that means another year of climate chaos, including a second dry and dangerous fire season for Los Angeles and a host of hurricanes to batter the Atlantic coast.

"La Nina may be temporarily down, but she's definitely not out,'' said Bill Patzert, a research oceanographer with the Jet Propulsion Laboratory.

The weather phenomenon, marked by cooler-than-normal temperatures in the eastern Pacific Ocean, appeared to be ebbing in the spring. But new satellite photographs show it regaining strength that should carry it until the end of the year, if not beyond.

La Nina's return to Southern California has good and bad repercussions:

"The good news is it's milder and cooler,'' a local summer effect of La Nina, Patzert said. "The bad news is we could always use the rainfall. When we go into our second year of below-normal rainfall it's not good news for the people who have to fight the brush fires.''

Despite the droughts, floods, hurricanes and other weather-related mayhem, the world's climate isn't out of whack, any more than the doomsayers predicting another ice age in the 1970s were correct.

Comment: We know better now, don't we?

"We go through cycles where it's more one way or another,'' said Joseph D'Aleo, chief meteorologist with the Maryland-based Weather Services International. "As you look back in history you see periods of extreme conditions. But long term, there's not a lot of evidence we're much more extreme.''

For example, 1954, 1955, 1964, 1975 and 1988 were all La Nina drought years, he said.

La Nina and EL Nino do their work by pushing around the jet stream, the high-level, high-speed current of air that flows across the United States. Normally it carries cold air from Canada through the Midwest, where it zooms far enough south to gather some warm, moist air from the Gulf of Mexico.

But La Nina has pushed the jet stream north, so it can't reach the rain-making warm air from the Gulf. The result - a choking drought that has scorched the Midwest and Northeast.

In Delaware, Gov. Thomas Carper on Thursday declared a drought emergency and mandatory water restrictions for two-thirds of the state's estimated 724,000 residents. Maryland announced statewide emergency restrictions Wednesday. And other states have enacted similar rules, following drought conditions.

Other parts of the United States and world get a soaking under La Nina's watch. Forecasters predict it will create a busier-than-normal hurricane season this year for the Atlantic seaboard.

When the jet stream is flowing farther south, like during an El Nino year, it stirs up the air over the Atlantic and knocks the tops off forming hurricanes, Patzert said. But in a La Nina year, like this, the jet stream is out of the area and the hurricanes have relatively calm air in which to form and strengthen, he said.

La Nina has already been battering Asia with fearsome storms, which it has spawned by other means, said Klaus Weickmann, meteorologist with the Climate Diagnostic Center, a National Oceanic and Atmospheric Administration lab in Boulder, Colo.

Weather systems that generate monsoon rains and cyclones in Asia shy away from La Nina's cool water, he said. They remain in the warmer waters of the western Pacific, cozying up against the land in Asia. Then they batter it with more rain than during a normal year, when some of the storms can dissipate offshore.

This week a monsoon in North Korea killed 42 people, while at least 71 died in the Philippines after landslides, flooding and four days of rain. In South Korea, 29 inches of rain fell from Saturday to Tuesday, submerging entire villages and leaving 3,000 homeless. Scores more were killed in Vietnam, Thailand and Cambodia.

And in China, flooding from storms throughout the summer has killed 725 people.

The bountiful rain from El Nino sprouted more vegetation on area hillsides. But all that greenery dried out in the arid La Nina winter last year, leaving hillsides covered with kindling.

Another dry La Nina winter, which forecasters expect this year, would increase the wildfire danger even more throughout Southern California.

"That's the way Mother Nature works,'' Patzert said. "She spanks you, and then she rewards you.''