'Godzilla' El Niño to soak SoCal this winter?
Anomalous zonal wind speeds, averaged between 5S and 5N across the equatorial Pacific. Reds are westerly wind anomalies. Note the 4 main westerly wind bursts between 140E and 180 (the date line).
By now you've heard it: We're going to get a monster - some say 'godzilla' - El Niño this year that will rival the beast from 1997-98. While some of the hyperbole is probably unwarranted, it is true, all the ingredients for a strong El Niño to persist through the northern hemisphere winter are present.
First, a quick El Niño recap: El Niño occurs when the ocean waters of the Eastern Pacific, which are normally much cooler than the waters to the west, warm up. The 1997-98 El Niño saw Eastern Pacific ocean temperatures spike to 2+ degrees Celsius above normal during the peak. These anomalously warm water temperatures sparked all sorts of changes to weather patterns across the globe.
New research has shown that "westerly wind bursts" may be the main driver of initiating and sustaining an El Niño. So what is a "westerly wind burst"? Well, a WWB (scientists love acronyms!) occurs when the normally westward-blowing (from east to west) winds of the central and western Pacific reverse course and blow from west to east (westerly). Sometimes, these bursts can be quite strong. So far this year (2015) we have had 4 major WWBS (see the figure at the left). The first was in March, the second in May, the third in early July and now the fourth in early August. The current WWB may be the strongest yet.
These WWBs force warm ocean water from the western Pacific to move eastward in the form of what we climate scientists call a "Kelvin Wave". As the Kelvin wave propagates eastward it warms up the cooler Eastern Pacific and voila! - El Niño is born!
But now, you're probably wondering, why is this year's El Niño going to be so strong? The answer is: we don't really know, but, we do know that a number of atmospheric factors have colluded, and that all the models are now forecasting a strong/very strong El Niño to persist through the northern hemisphere spring. Whether or not it will be record-breaking, or 'Godzilla' remains to be seen.
What does this mean for California, though?
Here's where things get tricky. We only really have two good analogs for this type of event: 1997-98 and 1982-83. These were the two strongest El Niños on record, and both brought about 2x the normal winter rainfall to the Golden State! All good, right? Not so fast.
1. Because the sample size is so small, we don't have a good handle on what this year's El Niño might bring. All signs point to a super wet winter, but only time will tell if that will bear out.
2. Even if we *do* get 2x the normal rainfall, our drought is so bad, that we would need 2.5-3x the normal rainfall - and that, most likely, AINT HAPPENING.
Looking at the "Standardized precipitation index" (figure on the right) for the past 48 months we notice that most of California is between 1.5 and 3 standard deviations away from normal! This is an incredible deficit to try and make up in one year!
Even a strong El Niño (very likely to happen) that brings soaking rains (somewhat likely to happen) is UNLIKELY to completely eliminate the drought.
*waa waa*
The 48-month standardized precipitation index, which is the number of standard deviations that the observed value would deviate from the long-term mean, after a transformation.
All that being said, for us weather weenies, the coincidence of a strong El Niño and a wet winter in California will be a welcome reprieve from the past 3 years of 90+ degree days in January and lame winter storms. Already this summer the weather has been unusually exciting, and we're all hoping for that to continue through the winter, when we need it the most!
A map of sea surface temperature anomalies for the past month showing a strong El Niño taking hold in the Eastern Pacific. Some areas are experiencing temperatures more than 3 degrees Celsius above the mean.