Hello everyone my name is Brandon Brady and I am a meteorology student at Mississippi State University. My family and friends have asked me what’s EL NINO. They said to me they heard their local TV meteorologists say we are in a EL Nino weather pattern according to the NOAA. I will do my best to extrapolate and discuss information in what El Nino is and what impacts we can typically expect from El Nino, so everyone can understand. In historical, philosophical, and faith based terms EL NINO means “Christ Child”. In climate and weather terms EL Nino is part of a global atmospheric circulation pattern that affects the weather at great distances from Peru and Ecuador. In another words it is a large climate and weather teleconnection where a set of climate conditions in one place affects weather and climate all over the globe. What I am going to discuss is what typically happens with El Nino events, because no 2 or more El Ninos are alike. Why? Because El Ninos vary in strength and intensity, from weak, moderate, strong, to very strong or super. The last very strong or Super Nino we had was the 1997-1998 event, that saw tornadoes in Central Florida, incredibly powerful storms in California, Texas and the Desert south west during the winter. In the summer we witnessed an unusual high fire season across the Southeast and Florida.
- What is El Nino or ENSO?
El Nino or El Nino Southern Oscillation occurs when the Barometric Pressure or Pressure over the Eastern Pacific near South America and the Western Pacific near Australia flip flops or switch. In neutral conditions, the pressure in the Eastern Pacific near South America are relatively high and the Sea Surface Temperatures(SSTs) are relatively cool due to a cold ocean current, causing a lack of precipitation. In comparison the Pressure near Australia in the Western Pacific are relatively low with warm Sea Surface Temperatures(SSTs) causing an abundant amount of precipitation. The normal monsoon in the West Pacific is thriving in these neutral conditions. Furthermore, in neutral Pacific conditions trade winds, which blow from east to west near the equator go undisturbed. In an El Nino pattern, Pressures decrease in the Eastern Pacific near Peru and Ecuador and Pressures increase in Darwin Australia, thus disrupting the trade winds and a strong countercurrent of a warm pool of water is pushed to the Eastern Pacific near Peru and Ecuador. As stated above precipitation is enhanced in Peru and Ecuador where it is normally dry due to lower pressures and warmer SSTs. Conversely higher pressure and drought are experienced in Australia and SE Asia disrupting the monsoon season during El Nino.
2. Sea Surface Temperatures(SSTs)
Another signal of an El Nino teleconnection is Sea Surface Temperatures. Just a note, NOAA needs to observe 3 consecutive months of above normal SSTs and lower pressures in the Pacific Ocean Regions to be named El Nino. The strength of an El Nino is determined by pressure and SSTs. The Warmer the SSTs the stronger the El Nino event. The same applies with pressure, the lower the pressures the stronger the El Nino event. Typically from 0.0 – 1.0 degrees Celsius above normal is considered a weak el nino, 1.0 – 1.8 degrees Celsius above normal is considered moderate el nino, 1.8 – 2.2 degrees above normal is considered strong el nino, and above 2.2 degrees normal is considered very strong or super nino.
3. SOI (Southern Oscillation Index)
The SOI or Southern Oscillation index is a measure of Barometric Pressure in the Pacific Ocean Basin at 2 different locales, Darwin Australia and Tahiti. This numeric value is provided daily by a positive and a negative value. The negative number indicates the lower pressure and the positive number indicates a higher pressure. Negative numbers indicate El Nino conditions and Positive numbers indicate neutral or LA NINA conditions opposite of El Nino.
4. Weather Conditions in the United States during EL NINO years
I am going to write and discuss what occurs in the Winter and Summer in the United States during El Nino years and not so much globally because I will be here all day and I don’t have that much time. So typically speaking El Nino conditions from December to February in the U.S. are as follows:
A. Cooler and wetter than average in the Southern U.S., with severe weather, including supercells thunderstorms and tornadoes in the Southeast and Florida due to a strengthening Subtropical Jetstream.
B. Warmer than normal Temperatures in the Pacific Northwest and the Northeast as well as drier than normal precipitation in these areas. Normal to near normal temps and precip in the Ohio Valley and central plains.
C. Below normal temperatures and Above normal Precipitation in California and the Desert southwest including Texas. This is subject to change depending on strength and intensity of El Nino mentioned above.
Lastly I am going to discuss and evaluate 5 climate and weather patterns affected by EL NINO.
- Enhanced Rainfall over California – Historically moderate to strong El Nino events have increased precipitation over California and the Desert Southwest by 7-10 Percent. Given the water shortage emergencies in California this is welcomed news.
- A Below Normal Hurricane Season in the Atlantic – Due to a Pacific El Nino, this sets up higher vertical wind shear and stronger Atlantic trade winds as well as greater stability and higher pressures in the Atlantic.
- A milder than Normal Winter for the U.S. – During normal El Nino events the Polar jet stream is displaced or moved further north allowing a flow component from the south or southwest ushering in milder temperatures throughout the U.S., except for the Southern tier due to the strengthening sub tropical jet stream where it is damp, cloudy and cool relatively speaking.
- Reduced Tornado Numbers – During a moderate to strong El Nino tornado numbers are down up to 25 percent. You can clearly see that this year with tornadoes down 20-25%. This may there is an uptick in tornado numbers but the season in whole has been well below average.
- An Extremely Active Pacific Typhoon Season – Due to the fact this year the entire pacific ocean basin has been well above average some +4 degrees Fahrenheit in the Western Pacific this year and 3 degrees above normal in the Eastern Pacific we could see a blockbuster year. There has already been several super typhoons from Maysak to Dolphin. So the trend looks to continue.
The Current forecast computer models indicate a strong EL Nino but these teleconnections continue to evolve and change so all we can do is monitor it, and understand the weather and climate associated with it. So be safe, stay well and until next time be good.