( El Niño has already arrived. )
~by Taigne Hammock
This year’s El Niño is helping to drive the rain that has flooded parts of Texas and Oklahoma, and has delivered a couple of unusual storm systems to Southern California as well. The Houston area was hit particularly hard over the Memorial Day weekend, ending a five-year drought and flooding local reservoirs and rivers. Some parts of Texas have received more than 20” for the month of May, making this the wettest month ever on record for the state.
2015-05-26: efore & after photos of flooding in Houston, Texas
Images courtesy David “Pfish” Terry
And with Pacific sea-surface temperatures still rising, and El Niño conditions continuing to strengthen, more rain is on the way for the southeastern United States. Although it’s still a little soon to make very accurate long-term predictions, the NOAA models are already predicting a 90% chance the current El Niño will continue through the summer of 2015, and a better than 80% chance that it will continue through the end of the year.
An El Niño event represents a tremendous amount of heat energy that gets released from the ocean into the global atmosphere. In general, this tends to generate warmer temperatures on a global scale. And, with the recent news that 2014 was the warmest year since 1880, that could mean 2015 will be even warmer still. Parts of southern India are already suffering a terrible heat wave, where temperatures have soared above 120°F (49°C) in some areas. And South Africa is experiencing their worst drought in more than twenty years with predictions of it becoming more dire in the coming months.
So while the rain forecast is a welcome relief for drought-stricken parts of the United States, it definitely comes at a price: huge amounts of rainfall in dry areas can produce flooding, mudslides and other chaotic scenarios, while the cooler ocean temperatures in the western Pacific Ocean tend to dry-out regions in Africa, Australia Southeast Asia, creating heat waves in the northern hemisphere and drought and fires south of the equator. Additionally, the abrupt change in weather can wreak havoc on regional and global agriculture commodities and even mining.
Although we’re just at the earliest outset of the full duration of this months-long weather event, Texas has already received record amounts of rain, as will the southeast and west coast in coming months. Coastal areas of Ecuador and Peru in South America will also be hit with heavy rain later this year. On the other side of the world, drought has already gripped South Africa. Dry conditions are forecast to persist for months there, in Australia and in Southeast Asia as heat waves are already claiming thousands of lives in India. And as the El Niño releases all of this heat energy stored in the Pacific, global climate models predict that 2015 could follow 2014 as the warmest year on record.
El Niño generally describes a weather pattern that forms every two-to-seven years along the equatorial waters of the Pacific Ocean. In neutral years when there is no El Niño formation, low pressure dominates the region near Indonesia, which draws the surrounding air in and creates a flow of trade winds that moves from east (South America) to west (Indonesia) known as a Walker Circulation cycle. These trade winds push the surface water west, bringing huge amounts of energy and moisture along for the ride, which helps drive the monsoon seasons in Southeast Asia and Australia. On the other side of the ocean, as warm surface waters are swept west by trade winds, sea surface temperatures in the eastern equatorial Pacific Ocean are moderated, and deep colder water rises closer to the surface.
During El Niño years, the scenario reverses and high pressure develops over the equator near Indonesia. The change disrupts the east-to-west windflow, and can sometimes reverse it. Once the exchange of energy from east to west is disrupted, warm waters accumulate along the equator in the eastern Pacific Ocean. The warm sea-surface temperatures evaporate huge amounts of water into the atmosphere, where wind patterns then move the clouds over land, terminating the supply of energy (heat). Rainfall occurs over western Peru and Ecuador in South America, and a much larger area over North America ranging from Baja and Northern Mexico in the south, to Northern California and stretching across the southeastern United States to Florida.
Nino Regions. Image source NOAA.
Pacific wind speed, direction and sea-surface temperatures (SST) are measured across the equatorial Pacific by roughly seventy moored buoys maintained by the Tropical Atmosphere Ocean project. The Pacific is divided into four “Niño” zones, which represent the overall conditions within those regions. Scientists look to the area between zones three and four, aka Niño 3.4, to give an indication of the larger picture and what might be expected in the coming months. The Oceanic Niño Index (ONI) is a three-month temperature average of sea-surface temperature (SST) within these regions. When the ONI is 0.5°C above average temperature in Niño 3.4 for five months in-a-row, El Niño conditions officially exist. That condition occurred at the end of March 2015, which means the El Niño pattern has been in effect for more than 6 months at this point:
Source: NOAA/National Weather Service
With the warm waters in-place, the latest graphics from NOAA reveal prevailing winds are also shifting, demonstrating the flow of trade winds that usually move from east-to-west is changing and reversing in the eastern Pacific:
Image source NOAA
Warm Pacific sea-surface temperatures (SST) along the southern Mexico coast are supplying moisture into the upper atmosphere, helping to fuel the recent torrential rains in the United States:
And sea-surface temperature (SST) anomalies are beginning to resemble a classic El Niño pattern. Here’s a map showing SSTA for 2015-05-26:
…and a map showing the anomalies from September 1997: