Sunday, March 23, 2014

"A super El Niño on the way? Subtle signs emerging"

As we said a few months ago, it won't arrive in time to modify the California fire season but may be good for some mudslides.
From the Washington Post:
Visualization of El Nino (NOAA)
Visualization of El Nino (NOAA)

Mashable’s Andrew Freedman has penned an intriguing and important piece suggesting the possible El Niño in the pipeline may be a doozy, comparable to the strongest ever recorded:
Since climate forecasters declared an “El Niño Watch” on March 6, the odds of such an event in the tropical Pacific Ocean have increased, and based on recent developments, some scientists think this event may even rival the record El Niño event of 1997-1998.
Recall an El Niño event is an episodic warming of the eastern tropical Pacific ocean, which often has worldwide weather implications.

Freedman interviews two scientists, Eric Blake from the National Hurricane Center and Paul Roundy from SUNY-Albany, who see early indicators reminiscent of the development stages of past whopper El Niño events.

One important possible indicator of the lead up to an El Niño is a reversal in the trade winds observed in the equatorial Pacific, from a prevailing easterly (from the east) to westerly (from the west) direction.  In recent weeks and months, there have been strong westerly “bursts”.
From Freedman’s piece:
“It’s something we haven’t really seen since the ’97 El Niño,” Blake said of the westerly wind bursts and ocean observations. Instead of having trade winds blowing from the east at five to 10 mph, some locations in the western Pacific have had winds from the west blowing at up to 30 miles per hour, Blake says. This is important because it has ripple effects on the sea and below the sea surface.
So impressed by the strong and persistent westerly winds, Roundy told Freedman he thinks there’s “around” an 80 percent chance of an unusually strong El Niño.

Separately, meteorologist Michael Ventrice from Weather Services International,  discusses a possible related harbinger of a big El Niño: a powerhouse eastward push of water, known as a Kelvin wave, under the sea surface.  This kind of underwater wave, triggered by the westerly wind bursts, is key for transporting warm water from the west Pacific to the east Pacific and getting an El Niño event underway.  But Ventrice stresses it needs some additional propulsion:
The current Kelvin wave in the Pacific Ocean has achieved the same strength as the one that preceded the 1997 Super El Niño event. This is an extremely rare feat but there still has to be a number of things to happen before we can say we are headed towards a strong El Niño. We need to see the continuation of strong westerly winds near the Equator over the Central Pacific to keep the momentum forward.
In Freedman’s piece, Blake and Roundy emphasize that a strong El Niño is no sure thing....MORE
Also via the WaPo: 
El Niño's effects on North America

Generally speaking El Niño brings:
  • cooler and wetter weather to the southern United States
  • warmer weather to western Canada and southern Alaska
  • drier weather to the Pacific Northwest
  • cooler weather to northern Canada
  • wetter weather to southern California
These effects are felt strongest in the winter after onset of the event. The Atlantic hurricane season is usually diminished during El Nino, while the tornado season is more active.
The following animations will show the temperature (in Celcius) and precipitation (in centimeters) departure from normal over the entire North American continent.
The time starts from the fall season after onset (OND) on through the following summer (JAS).

El Niño on North American temperature
El Niño effects on North American precipitation