Weather Around The World, 4/21: El Niño Strengthens; No Cyclones In The Tropics; Record Rain In Atlanta

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Home / Weather Around The World, 4/21: El Niño Strengthens; No Cyclones In The Tropics; Record Rain In Atlanta
2015 El Niño

Water temperatures across the equatorial Pacific are above normal: El Niño Eggplant. Analysis courtesy of NOAA.

Since Edward Lorenz did his seminal work on chaos theory in 1961, it has been known that tiny changes in the weather in one place can affect the weather in far off locations.

Lorenz called it the butterfly effect, because a disturbance as small as a butterfly unexpectedly flapping its wings somewhere could set off a chain of events leading to fair or foul weather on the other side of the globe.

So it should not be a surprise that a fairly substantial change in one part of the ocean-atmosphere system can create changes in the weather on a global scale.

El Niño Eggplant Is Getting Stronger

Water temperatures in the tropical Pacific Ocean have risen in the past few weeks; this and other indicators suggest that the El Niño will get stronger. NOAA puts the probability that El Niño Eggplant will continue through the summer at 70%, and the chance of its going through fall at 60%. Decoded Science rates the odds to be somewhat higher, with a better-than-even chance that El Niño conditions will last through the winter.

The latest temperature anomaly analysis shows above-normal sea surface temperatures across the entire equatorial Pacific. In addition, subsurface temperatures have increased in response to a downwelling phase of a Kelvin wave.

Kelvin waves propagate along the equator, trapped there by the change in sign of the Coriolis force from northern to southern hemisphere (a subject for another day). Kelvin waves are associated with the wind patterns in the central and western Pacific, which have now become more westerly than normal, another sign of a strengthening El Niño.

NOAA's precipitation forecast for September, October, November shows a greater than 50-50 chance of above normal precipitation in southern California. Forecast curtesy of NOAA.

NOAA’s precipitation forecast for September, October, November shows a greater than 50-50 chance of above normal precipitation in southern California. Forecast courtesy of NOAA.

El Niño Eggplant is still at minimal strength by NOAA’s criteria. But the recent evolution leads Decoded Science to predict that Eggplant will be a significant player in worldwide weather into next winter.

There are already signs that the persistent drought pattern in the western United States is breaking down; some rain is likely in southern California this week. Since summer is the dry season there, any rain would be welcome in the next six months. But next winter could see a return to average or above average rainfall, and though one rainy season will not eliminate the drought, it would be a start.

No News Is Good News: Tropics Unusually Quiet

The weather doesn’t normally make headlines when there isn’t any, but today’s tropical weather is notable for a complete absence of any disturbed weather that might lead to cyclonic activity.

The southern hemisphere’s tropical cyclone season is waning; but the northern hemisphere’s will soon ramp up.

El Niño And The Atlantic Hurricane Season

The connection between El Niño and rain in California is well-established. The warm water initiates a low-latitude jet stream which carries moisture from the deep Pacific to the US west coast. Since it appears as though there is a direct pipeline from Hawaii to California, this is often referred to as the Pineapple Express.

El Niño is also correlated with weaker than normal hurricane activity in the Atlantic — but the relationship is not as strong as with the Pineapple Express. If the low-latitude jet stream persists across the southern US and into the Gulf of Mexico and Atlantic Ocean, it can inhibit hurricane formation. However, there are many more factors. Last season was rather quiet because of dry African air that invaded much of the Atlantic Ocean.

Water temperatures in the southwest Atlantic and the Gulf of Mexico are above average. Graphic courtesy of NOAA.

Water temperatures in the southwest Atlantic and the Gulf of Mexico are above average. Graphic courtesy of NOAA.

The water temperatures are currently above normal over much of the Atlantic, and particularly the Gulf of Mexico, a factor normally associated with above-average hurricane activity.

As a result of the conflicting signals, Decoded Science will not make a prediction for the Atlantic hurricane season until there is more evidence on the table.

Parts Of The Soggy South Finally Dry Out

Two weeks ago, Decoded Science named Severe Weather Outbreak Jon, which at its peak brought an EF4 tornado to Illinois. We suggested that a second outbreak was possible in a week (which would have been last week). As it turned out, that weather system was more rain than violent weather, though there were some severe thunderstorms and a few relatively weak tornadoes.

The rain continued for five days, with accompanying flooding. The pattern that brought that rain has been more or less in place since January, as humid air has repeatedly surged into the Gulf states and beyond. Atlanta has now had its rainiest first four months of the year since meteorologists first began keeping accurate records — 54 rainy days.

The winter weather pattern which brought so much snow to the northeast, but only occasionally impacted the south, will push drier air into the Atlanta area today and there will finally be a couple of nice spring days. However, another wave in the jet stream will begin to impact the southern plains today as moisture once again streams north, and the rain will return to all of the south during the week, possibly accompanied by severe weather.

Changing Weather In Europe And Asia Minor

The weather in Europe has turned decidedly colder in April (relative to normal). Moscow has had more days below normal this month than in the first three months of the year combined.

The Balkans and Turkey experienced a particularly rainy and snowy March. Precipitation records were broken in many Serbian cities, including Belgrade, as a persistent low pressure area refused to move. The change of pattern is bringing cooler and drier weather to the region.

Spring Brings Atmospheric Instability

As the surface of the northern hemisphere heats in response to the climbing elevation of the sun, some of that heat is transferred by conduction to the lower atmosphere. The upper levels of the atmosphere lag in warming, and the result is a steeper lapse rate (greater decrease of temperature with height), and thus a greater chance of instability. As humid air pushes north into the eastern US, waves in the jet stream provide the lifting that begins the process of severe weather formation.

What’s the weather like where you live? Let Decoded Science know if you see anything interesting.

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