28 May 2015

El Nino’s influence: more Pacific hurricanes likely this year

As I write this, the first tropical depression of the Pacific ocean hurricane season is lurking in the eastern Pacific.

While it’s not expected to become a monster storm, it marks the beginning of a hurricane season that is likely see a greater number of storms than normal – largely due to the presence of El Nino.

The Pacific ocean hurricane season runs from 15 May to 30 November each year, so even though the first storm of the season isn’t early, it shows that conditions in the region are now favourable for storm formation.


An active hurricane season expected

Yesterday, the National Hurricane Center issued its eastern Pacific hurricane outlook, saying that there’s a 70 per cent chance of an above-normal number of storms this year.

As expected, it highlights El Nino as the main climate factor that will enhance this year’s season – especially as El Nino is forecast to strengthen through the coming months.

El Nino’s presence will offer two influencing factors that will favour a more active hurricane season: warmer than normal sea surface temperatures and less wind vertical wind shear.

Conditions favourable for storm formation

Warmer than normal sea surface temperatures add extra heat energy to the atmosphere above, which means that storms have more energy to draw on and thrive.

Vertical wind shear is a measure of how wind direction and speed changes with height in the atmosphere.

global_sst_NOAA_wpIf wind shear is strong, storms experience a tug of war effect, as winds blowing in different directions mean that storms are torn apart before they can develop significantly.

However, less vertical wind shear, as is expected to be the case this year, means that this effect is reduced, making conditions more favourable for storm formation.

El Nino: this year’s weather buzzword

You’ll be hearing a lot about El Nino this year, as its effects on global weather patterns reach far and wide across the globe.

One of the biggest influences it is likely to have is increasing global annual temperatures – probably leading to our planet equalling or surpassing its warmest year on record.

monsoon_rain_g_wpIn India, the presence of El Nino often causes monsoon rainfall to be below average, which the Indian Meteorological Department thinks will happen this year.

For a country that relies heavily on these rains for agriculture, this is worrying. If agriculture is negatively affected, this has the potential to affect food supplies and prices around the globe.

There are also fears that rainfall patterns in equatorial Africa will be hit, threatening drought to areas that have little water at their disposal in the first place.

I’ll be keeping a close eye on El Nino in the coming months, with updates here on my blog and on Twitter – @liamdutton

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