Jun 9, 2016

June 2016 ENSO discussion: The new neutral

Kiribati
by
Emily Becker
,
NOAA Climate.gov
Equatorial Pacific sea surface temperature, 2015-2016 (left) compared to 1997-1998 (right). Each row in this type of image is the departure from average at that time. Weekly data is shown starting in January 2015 and 1997 (top). Data ends at the end of May 2016 (left) and end of June 1998 (right). Image: Climate.gov, CPC data
Equatorial Pacific sea surface temperature, 2015-2016 (left) compared to 1997-1998 (right). Each row in this type of image is the departure from average at that time. Weekly data is shown starting in January 2015 and 1997 (top). Data ends at the end of May 2016 (left) and end of June 1998 (right). Image: Climate.gov, CPC data

We’re sticking a fork in this El Niño and calling it done. After spending more than a year above average, sea surface temperatures in the central and eastern equatorial Pacific had mostly returned to near average by the end of May. Forecasters don’t think we’ll remain in neutral territory for long, though. There’s an approximately 65% chance that sea surface temperatures will drop into the La Niña realm (more than 0.5 degrees below normal) by the July – September period. This chance increases to around 75% by the fall.

I’ll get into what’s behind these numbers in a bit, but first, let’s bid a fond farewell to the big 2015-2016 El Niño.

The king is dead!

As we’ve reiterated many times in this blog, the El Niño/La Niña (ENSO) cycle is characterized by the changes in tropical Pacific temperatures and the corresponding response of the atmosphere. During El Niño, atmospheric changes include weaker trade winds and upper-level winds, more convection and rainfall in the central or eastern Pacific, and drier conditions over the far western Pacific and Indonesia. Over the past few months, the tropical Pacific has cooled off rapidly, and all these atmospheric indicators returned to average conditions during May.