10 Jul 2015

El Nino’s warmth causing tropical trouble in the Pacific

As I write this, there are no less than six tropical disturbances in the Pacific Ocean basin – ranging from minor tropical depressions, to raging typhoons.

Whilst they all have different locations and strengths, the one common denominator that drives them all is the warm ocean water that sits beneath them.

Warm ocean waters are one of the most important factors in driving tropical storms – giving a source of warm, moist air with sea surface temperatures of 27C or more.

The supply of heat and moisture effectively act as fuel for any potential storms. This is why tropical cyclones die when they move over land, as their energy supply is cut off.

Six tropical disturbances

The most significant activity at the moment is in the north west Pacific Ocean, in the vicinity of China and Japan, where there is a dying tropical storm, Linfa, and two typhoons, Chan-hom and Nangka.

Typhoon Chan-hom and Nangka are pictured below (from left to right), with Chan-hom set to hit the east coast of China, close to Shanghai, on Saturday (local time), giving damaging winds, torrential rain and a coastal storm surge, bringing a risk of flooding.


Nangka, for now, is no threat to land, sitting out across open waters. However, it could affect Japan in around a week.

At the other side of the Pacific Ocean, three minor tropical depressions are eerily surrounding Hawaii – each represented by a swirl in the picture below.


None of them pose a huge threat to Hawaii, although the one to the north east of the islands could enhance rainfall into next week.

El Nino’s influence

El Nino is a naturally occurring ocean-atmosphere phenomenon that is characterised by unusually warm surface water temperatures in the central and eastern Pacific.

It is important because it has a significant impact on the climate in many parts of the world.

In the case of tropical storms in the Pacific Ocean, the presence of El Nino not only makes them more likely to form, but can also global_sst_NOAA_wpmake them stronger.

This is because 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.

In addition, the presence of storms can actually increase the strength of El Nino, as they reinforce westerly winds which pile up warmer water towards the coast of South America.

Yesterday, the US weather service NOAA said that there is a greater than 90 per cent chance that El Nino will continue through the northern hemisphere winter, with an 80 per cent chance that it will last into early spring 2016.

Not only is El Nino expected to persist for a significant amount of time, it is also likely to be a strong event, with its influence on the world’s weather being felt most strongly within the tropics.

For more updates on weather around the world and in the UK, you can follow me on Twitter – @liamdutton

Images: earth.nullschool.net, NOAA

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