There Goes El Nino, Here Comes La Nina

Forecasters Expect Nino's "Evil Twin Sister" To Bring More Hurricanes, More Drought

(AP)  Forecasters warned Tuesday that a La Nina weather pattern — the nasty flip side of El Nino — is brewing, bringing with it the threat of more hurricanes for the Atlantic.

Officials at the National Oceanic and Atmospheric Administration announced the official end of a brief and mild El Nino that started last year. That El Nino was credited with partially shutting down last summer's Atlantic hurricane activity in the midst of what was supposed to be a busy season.

"We're seeing a shift to the La Nina, it's clearly in the data," NOAA Administrator Conrad Lautenbacher said. La Nina, a cooling of the mid-Pacific equatorial region, has not officially begun because it's a process with several months with specific temperature thresholds, but the trend is obvious based on satellite and ocean measurement data, he said.

"It certainly won't be welcome news for those living off the coast right now," Lautenbacher said. But he said that doesn't mean Atlantic seaboard residents should sell their homes.

Forecasters don't know how strong this La Nina will be. However, it typically means more hurricanes in the Atlantic, fewer in the Pacific, less rain and more heat for the already drought-stricken South, and a milder spring and summer in the north, Lautenbacher said. The central plains of the United States tend be drier in the fall during La Ninas, while the Pacific Northwest tends to be wetter in the late fall and early winter.

Of special concern is west Texas which is already in a long-term drought, which during a La Nina will likely get worse, Lautenbacher said.

Historically, El Ninos and La Ninas are difficult to forecast, said National Center for Atmospheric Research senior scientist Michael Glantz, who studies how they effect humans.

"I don't see it as a useful forecast," Glantz said. "Every event since they've been looking at El Nino ... surprised scientists."

La Ninas tend to develop from March to June and reach peak intensity at the end of the year and into the next February, according to Vernon Kousky, NOAA's top El Nino/La Nina expert. La Nina winters tend to be warmer than normal in the Southeast and colder than normal in the Northwest.

Andrew Weaver, a meteorology professor at the University of Victoria in Canada, said NOAA's forecast looks good because the signs of a brewing La Nina are apparent just below the ocean's surface.

"La Nina is the evil twin sister of El Nino, so it's good or bad depending on where you live," Weaver said. However, in general La Ninas do not have as costly effects on humans as El Ninos do, he said.

The last lengthy La Nina, from 1998 to 2001, helped cause a serious drought in much of the West, according to NOAA drought specialist Douglas Lecomte.

"There are winners and losers, people tend to concentrate on the losers," Lautenbacher said.

[gramto7]

n normal, non-El Niqo conditions (top panel of schematic diagram), the trade winds blow towards the west across the tropical Pacific. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1/2 meter higher at Indonesia than at Ecuador.

The sea surface temperature is about 8 degrees C higher in the west, with cool temperatures off South America, due to an upwelling of cold water from deeper levels.

During El Niqo (bottom panel of the schematic diagram), the trade winds relax in the central and western Pacific leading to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. The result was a rise in sea surface temperature.

La Niqa events occur after some (but not all) El Niqos

http://www.pmel.noaa.gov/tao/elnino/la-nina-story.html

[pensacola8-2009]

I saw an episode on NOVA 15-20 years ago stating that the El Nino traces its' orgin off the Chilean coast with Sub-Marine volcanoes that exist off the coastline and release intense amounts of heat into the water. The warm water rises to the surface and gets carried westward by the currents across the Pacific Ocean. The El Nino weather pattern changes the Hadley Cell patterns. Has anyone got any updated material about this? Everything I was led to beleive is that we get either one pattern or the other-based on what the volcanoes off the Chilean Coastline are doing. It is like a light switch that turns a weather pattern off or on.