I received an email recently asking: When the El Nino pattern ends how long before we experience the reverse pattern, La Nino in addition does this mean a return to normal rain and temperatures?
I want to first explain briefly what the two weather patterns are, keep in mind this definition is very brief and I am not an expert on the subject. But do find it interesting and it reminds me of how fragile the line between sustainable weather and destructive weather can be. El Nino is a large body of warmer than normal water in the Eastern Pacific. This area is about 1 1/2 times the size of the United States. Yes, much larger than what is generally understood. It begins when every three to five years the Tropical Trade winds abate and warm water normally found near Australia spreads outward along the equator in the Pacific. Sometimes when the El Nino is strong the warm water reaches as far as Ecuador and Peru.
On the other side La Nina, which is typically stronger during our Winter season, is also much less understood. I always found it easier to have a basic undertanding for El Nino & La Nina, is that having any other weather pattern than normal will bring extremes to what is normal weather for that area.
El Nino increases rain producing clouds for most but also increase the Tropical Trade Winds along the Atlantic Ocean suppressing the formation of Hurricanes.
La Nina weather pattern typically last one to two years. you might remember the 1988 Mid-West Drought. Also the lighter winds are more favorable for Hurricane formation in the Atlantic. 1992 researchers says that a strong El Nino was present. That year in August Hurricane Andrew made landfall first in South Florida then here in Acadiana. Andrew….an A storm in August yes, fewer storms but it only takes one to make the season devastating. Interesting to know also that Hurricane Andrew before making landfall in South Florida almost weakened to just rain. As it moved a little north and out of the hostile winds it strengthened to the record Category 5 storm.
What generally follows El Nino is the return to normal water temperatures and weather pattern. Not always going from La Nina to El Nino. Yes, we do have normal weather patterns. The research is getting much better now so telling one pattern from the other is closer than ever. In the past 20 years the have been just three La Nina’s and seven El Nino weather patterns.
During an El Nino the energy from the warmer water is pressed high in the atmosphere and directed with pressure eastward where it settles over the Tropical Atlantic and the release of energy tends to choke the formation of Tropical Storms which are very weak in the beginning stage.
The Earth is always trying to balance and for that we get the movement of storms and transfers of energy.
My understanding was that El Nino generally meant wetter and warmer than average winter weather. Seems quite cold this winter. Can you explain?
Justin Fontenot
31 Jan 10 at 9:06 am
Justin, typically after it all averages out from December through February during El Nino years we will indeed see wetter than normal conditions and generally milder conditions. Usually highs will be cooler than normal with the cloud cover associated with wet weather patterns while overnight lows are milder due to the clouds. December was certainly wet and colder than normal, January was near normal all around, while so far it’s been wet and colder than normal this February. This winter is just hilights the variability of weather and that larger scale patterns can overcome a significant El Nino pattern. Plus El Nino may indeed be fading to a degree…and that has opened the door for more in the way of arctic intrusions. If you look at the broad picture so far this winter…December in Acadiana looked like El Nino…but the rest of this year has been plain old-school winter!
Rob Perillo
10 Feb 10 at 8:07 pm