El Niño outlook 2015-16 Eric Boldt Warning Coordination Meteorologist Hello, this is Eric Boldt from the National Weather Service in Oxnard, CA. Here is a quick look at the El Nino status and predictions for the upcoming 2015-16 winter season for southwest California. Eric Boldt Warning Coordination Meteorologist National Weather Service Los Angeles/Oxnard August 20, 2015

Latest ENSO* Information El Niño Advisory in effect August 2015 El Niño Advisory in effect Ocean continues to reflect sustained and strengthening El Niño conditions Greater than 90% chance of an El Niño this winter Forecasters unanimously favor a “strong” category El Nino advisory is in effect. * ENSO stands for El Niño Southern Oscillation

Normal Pacific Pattern Let’s talk about what normal conditions look like across the equatorial Pacific Ocean. Trade winds push warmer water to the western Pacific closer to Australia, which in turn fuels the atmosphere resulting in more storm activity. Cooler water and subsiding air across the eastern Pacific do not bring as much storminess to that region.

El Niño Pattern During an El Nino, trade winds often weaken or reverse direction which allows the warmer water to move eastward toward the eastern Pacific coast of South America. This fuels storm systems across the eastern Pacific especially during the winter months and results in drier conditions over the western Pacific.

Global Satellite on August 12, 2015 Clouds A recent global satellite image confirms that more cloud cover and storminess are already occurring across the eastern Pacific as outlined by the red oval above. The attached graphic is a measurement of solar radiation in the last four weeks, with blue shading showing where there was cloud cover and orange shading a lack of cloud cover.

Sea Surface Temperature Anomalies Last Four Weeks Sea surface temp anomalies in the last four weeks remain above average across most areas east of the dateline. This is where we want to see this occurring and is a positive sign for El Nino.

Latest weekly (Aug. 17) value of Niño 3.4 region Sea Surface Temperature (SST) Anomalies – One Year This chart shows sea surface temps across different areas of the Pacific going back to last year at this time on the left side of the diagram versus current time on the right. After March, all areas saw increasing water temperatures and the latest numbers remain high. The Nino 3.4 region is an area monitored closely for El Nino and was last reporting 1.9 degrees Celsius above normal. El Nino conditions start at 0.5 degrees with a strong category beginning at 1.5 degrees. Latest weekly (Aug. 17) value of Niño 3.4 region is +2.0° C

Sub-Surface Temperatures in the Equatorial Pacific (0-300m) Another important measurement for El Nino is the “sub-surface” temperature anomalies in the equatorial Pacific Ocean. The top chart shows the upper ocean started to warm rapidly after mid-January and has remained above normal through the summer months. The lower chart indicates that warming down several hundred meters deep continues east of the dateline (180W).

Comparison of SSH - 1997, 2015 There have been comparisons made with the current sea surface height anomalies to those from 1997, which was the last strong El Nino and was well remembered for the impacts it had across southern California. The red shading shows the above normal sea heights (reflective of warming temperatures) across the eastern Pacific Ocean near the equator for August 1997 (left) and August 2015 (right). Note the differences in the eastern North Pacific Ocean region where sea surface temperatures are much warmer than in 1997. This could be a sign of the Pacific Decadal Oscillation shifting to a warm phase.

Pacific Decadal Oscillation Another sign that often helps El Nino in the rain department is the Pacific Decadal Oscillation or PDO. The PDO has been in a cold phase since the last strong El Nino back in 1997-98. However, in the past year the PDO has shifted toward a warm phase which is associated with the warmer sea surface temps we have experienced along the California coast. PDO working in conjunction with El Nino is a good sign for southern CA precipitation during the winter. - Warm phase past year - Cool phase since 1997

ENSO Model Predictions Strong Weak to Moderate Neutral Computer models are predicting that this winter’s El Nino could range from a moderate to a strong event. The unanimous forecaster consensus is above 1.5 degrees Celsius and near the 2.5 degree Celsius level or into a “strong” category El Nino this winter. Summer Winter

Classic El Niño Winter Impacts The classic El Nino winter impacts looks like this. When the warmer ocean water shifts eastward, the jet stream elongates and interacts with the eastern Pacific Ocean storms that then track across the southern sections of the country. More northern latitudes are typically warmer and drier than normal during an El Nino.

average 93-94

With El Nino predicted through the upcoming winter season, here is the precipitation outlook for the rainy season months of December through February. There is a greater than 40% chance of being wetter than normal across southwest California. Normal annual rainfall ranges from about 15 to 25 inches across the area.

The temperature outlook for the December through February time frame calls for having equal chances of being below, above, or normal temperatures for the season. A warmer temperature signal is shown across northern California.

Conclusions El Niño tilts the odds of above normal rainfall for southwest California this winter The strength of this El Niño is the most difficult prediction; favors a strong event One El Niño winter season will not end the drought (over 30” rainfall deficit in 4-years) Prior to the rainy season, we should be prepared for a dangerous wildfire season

805-988-6623 eric.boldt@noaa.gov weather.gov/losangeles Thank You! 805-988-6623 eric.boldt@noaa.gov weather.gov/losangeles @NWSLosAngeles weather.gov/losangeles NWSLosAngeles