This post was written byĀ Emily BeckerĀ for the NOAA ENSO Blog
Forecasters estimate a 70% chance that our current El NiƱo will continue through the summer and a 55-60% chance it will extend into the fall.
Just a number
El NiƱo conditions were still evident across the tropical Pacific Ocean during April, as the sea surface temperature in the NiƱo3.4 region averaged about 0.7Ā°C warmer than the long-term average (via the ERSSTv5 database). Most computer models predict that the ocean surface will stay warmer than average in the NiƱo3.4 region, with the majority of predictions remaining above the El NiƱo threshold of 0.5Ā°C through next fall.
- The nerd’s version… NOAA El NiƱo Update: El NiƱo is Likely to Continue Through the Summer and Fall
However, there is a broad range of potential outcomes shown here, and weāre still within the spring predictability barrier, when forecast models have a tougher time making successful predictions, partly due to the tendency of ENSO to be in transition during the spring. Weāre starting to pass that barrier, but we still bear it in mind when looking at forecasts made in early May.
Blow out your candles
The atmosphere also continued to reflect El NiƱo in April, with more clouds and rain forming over the warmer-than-average waters of the central tropical Pacific, and drier conditions over the far western Pacific and Indonesia, although this pattern was somewhat weaker than during February or March.
The near-surface winds in the tropical Pacific, the trade winds, were near average in April. The trade winds usually blow from the east to the west, keeping warm water piled up in the far western Pacific. Changes in these winds are a critical component of the El NiƱo system. When they weaken in the central Pacific, surface waters can warm, and sometimes allow a downwelling Kelvin wave to form: a large blob of warmer-than-average water that moves from the west to the east under the surface of the Pacific.
After a couple of months of weaker-than-average trade winds (what we expect during El NiƱo conditions), they were near average overall during April. This slight weakening of the typical El NiƱo signal is in part due to a reawakening Madden-Julian Oscillation (MJO) in the second half of April.
The MJO is an area of active storms and convection (rising air) that travels from west to east along the equator. It can circle the globe in about 30-60 days. Weāve talked about the MJO quite a bit on the ENSO Blog and climate.gov since this pattern can affect US weather, and interact with El NiƱo and La NiƱa.
Near-surface air is drawn toward the MJO-related area of convection. So when the MJO is over the Indian Ocean, the trade winds in the west-central Pacific are stronger than average, because the inflow to the MJO reinforces them. But when the MJO moves into the central Pacific, the trade winds tend to be weaker, because the inflow to the MJO opposes them.
After going mostly quiet in mid-March, by mid-April the MJO was showing signs of re-development. The trade winds in the western Pacific during mid-late April were stronger than average (more east-to-west), consistent with what weād expect when the center of MJO convection is in the Indian Ocean. However, during the first week of May, as the MJO moved into the Pacific, the trade winds weakened substantially in the west-central Pacific.
Over the hill
Over the past year, subsurface waters (from the surface down to about 1,000 feet) have remained warmer-than-average overall, but with some substantial increases and decreases,Ā resembling a particularly brutal stage of the Tour de France. If the recent weakening in the trade winds does lead to a downwelling Kelvin wave and increases the subsurface anomalies, it could provide fuel to help this El NiƱo event to persist. Bikers beware, another uphill climb may be ahead of you.
Bon anniversaire
Lastly, happy 5th birthday to the ENSO Blog! Weāve learned a lot over the past 60 months, and we hope you have, too. Weāve reported on a slow-to-develop, but strong El NiƱo; consecutive weak La NiƱas; and the current, weak El NiƱo. Weāve built an extensive catalog of posts on ENSO (the whole El NiƱo/La NiƱa system), other climate patterns, and many other climate-related topics. Ā Check out our editorās handy index page for a stroll down memory lane. And, never forget Tomās three–post series on forecast verification.
The best part is that we have a long list of topics weāre looking forward to covering in future posts, and weāre happy to solicit suggestions in the comments section below on topics you would like us to cover. Thank you for reading usāweāve had well over 2 million unique page views so farāotherwise, weād just be yelling into the (trade) winds.