2015-06-11 - By Martin Hedberg

El Niño reduces the risk of hurricanes in the Atlantic

A prognosis shows 70% probability for lower hurricane activity than normal, mostly due to El Niño, writes Entropics meteorologist Martin Hedberg. However, the main source of risk is the number of hurricanes that make landfall.

The official hurricane season in the Atlantic runs from 1st June to 30th November. But this year’s season got off to an early start with “Ana” on 8th May. Ana was also the second earliest hurricane on record to make landfall in North America.

But despite this early start it looks as if there will be fewer hurricanes than usual in the Atlantic this year. This is according to NOAA. NOAA’s prognosis shows about a 70% probability for hurricane activity being lower than normal and only a 10% probability that it will be higher than normal. This applies to the North Atlantic, the Caribbean and the Mexican Gulf. This is also in line with the forecasts from many other weather institutes.

Hurricane paths in the Atlantic 1851-2012. Source Wikipedia

Hurricane paths in the Atlantic 1851-2012. Source Wikipedia

The main reason behind this prognosis is the ongoing El Niño (see earlier article for more information) that indirectly decreases a number of factors that support the development of hurricanes in the Atlantic. El Niño is expected to gain strength somewhat and to continue throughout the hurricane season.

Despite the fact that El Niño is primarily a phenomenon that affects sea temperatures in the Pacific Ocean it also affects air pressures, jet winds and bodies of air over large parts of the globe. Over the Atlantic it creates powerful westerly winds, increased wind shear (different wind velocities and directions at different altitudes) and subsidence air. These factors counteract the formation of tropical hurricanes.

But El Niño does not take away the basis for tropical hurricanes – a layer of warm seawater far enough north of south relative to the equator. This means that we must still count on some storm activity. The prognosis from NOAA looks as follows (normal values in brackets):

  • 6-11 named storms (12)
  • 3-6 hurricanes (6)
  • 0-2 large hurricanes (3)
  • 40-85% ACE Accumulated Cyclone Energy

But it should be noted that it is not the total number of hurricanes that is the main cause of risk, it is the number that make landfall. A clear example that one should not assume zero activity was seen in 1992 where there were only seven named storms. However, the first of these was “Andrew” a category-5 hurricane that destroyed much of Southern Florida.

While several institutes anticipate reduced hurricane activity in the Atlantic, prognoses also show an increased likelihood for tropical hurricanes in the Pacific Ocean. This too is connected to El Niño.

To summarise we can conclude that, although the effect may not even out, the phenomenon El Niño has moved the risk for tropical hurricanes from the Atlantic to the Pacific.

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Martin Hedberg

Martin Hedberg

Chief Meteorologist

Martin has 20 years’ experience from meteorology and previous officer in Swedish Armed Forces, civil career as meteorologist at Swedish Television and as CEO for a commercial weather company. He also works as a climate expert and advisor about extreme weather and how climate changes affects society, finance and energy markets. Martin holds a Bachelor of Science with a Major in Meteorology from Stockholm University.

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