2015 Hurricane Season Limited by El Niño


After a quiet spring, the United States was hit with four severe weather events in the last week: tornadoes and torrential rains in the Great Plains; 2 feet of snow in the upper Midwest; Tropical Storm Ana developing in the Southeast; and New York City sweltering in 87-degree weather. These unusual events may be evidence that El Niño’s high atmosphere “wind shear” is beginning to cause cyclical changes that will bring much cooler weather and more precipitation.

It has been 6 years since a weak El Niño formed in the equatorial Pacific Ocean west of South America, and 18 years since a strong one. The last moderate El Niño event occurred during the summer of 2009. Temperatures fell to below-average across most of the U.S. Total population-weighted Cooling Degree Days (CDDs) from May-September that year clocked in at 4% below average.

All hurricanes start out as “named” tropical storms, with winds from 39 to 74 mph. They become hurricanes when winds top 75 mph. Tropical storm systems developing during the month of May happen only about once every 6.5 years. Before Ana, the last seasons to have a May tropical storms were 2012 and 2008. But early storms do not have much impact on the average of 11.2 named tropical storms and 6.3 hurricanes.

The primary influence on the upcoming hurricane season will be the presence of El Niño. This “macro-scale weather pattern” is characterized by warmer-than-average sea surface temperatures across the equatorial Pacific Ocean west of South America. One of the many impacts of El Niño on worldwide weather patterns is an increase in “wind shear,” which changes wind direction at higher altitudes across the tropical Atlantic and tends to inhibit tropical cyclone formation.

Building up since October, average “sea surface temperature anomalies” across the Pacific reached the required five-month average +0.5 centigrade (C) above average for the NOAA’s Climate Prediction Center to issue an El Niño Advisory on March 5. Since March, ocean temperatures have continued to warm, with anomalies now approaching the three month +1.0C threshold of a “moderate” El Niño event. The Climate Prediction Center has assigned a 70% chance the El Niño will persist this summer.

The Pacific Ocean warming is also coupled with the presence of below-average sea surface temperatures across the “Main Development Region” in the tropical Atlantic and Caribbean Sea, where the majority of strong tropical cyclones develop to threaten the U.S. With El Niño’s unfavorable upper-air environment for storms and cool ocean water temperatures limiting the available fuel for Atlantic cyclones, forecasters expect below-average storm activity this year, despite Tropical Storm Ana’s early arrival.

Global warming “scientific experts” became climate change “scientific experts” when their models failed to predict a 15 year world global warming “pause.” These scientific experts developed new models for climate change that predict severe spikes in droughts and hurricanes, because “Extreme Weather Is a Product of Climate Change.”

But the highly respected Colorado State University forecast for the coming season looks for only 7 named tropical storms and only 3 hurricanes, about 40% less than average. Coupled with the expectations of global cooler weather and more precipitation from El Niño, climate change “scientific experts” may need to develop more new models.


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