Weather extremes

A super El Niño on the way? Subtle signs emerging

Washington Post,

20 March, 2014

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. They point out the westerly winds could relax halting the El Niño’s formation.  Tony Barnston,  a climate forecaster at the International Research Institute for Climate and Society (IRI), offers Freedman this cautious assessment:

Unless we continue to get westerly wind events in the coming weeks, there is no guarantee that it will be a big event, and there is a 40% or so chance we will not get an El Niño at all

Officially, NOAA says there is just over a 50 percent chance of an El Niño of any variety, weak, moderate or strong. (Note: the normal chance of an El Niño would be 33 percent, since its parent weather pattern known as the El Niño Southern Oscillation or ENSO, has three phases: El Niño, La Niña, and neutral).

Suppose a strong El Niño event does materialize later this summer or fall.  What might it mean?

• Large amounts of heat from the tropical Pacific ocean would be released into the atmosphere, likely raising global temperatures to record-setting levels
• Above normal rain would be favored in California.
• Hurricane activity would likely be suppressed in the Atlantic
• Washington, D.C. might see depressed snow next winter.  Our two least snowy winters on record (0.1 inches at Reagan National Airport) coincided with two of the three strongest El Nino events on record (1997-1998 and 1972-1973).
• Link: List of El Niño impacts on North America

The possible development of El Nino is literally a fluid situation. Keep your eyes on the Pacific.