Why is Storm Ophelia an ex-hurricane and what is a sting jet?

16 Oct 2017

Image of hurricane over the Atlantic Ocean. Image: Allexxandar/Shutterstock

Despite its name, an ex-hurricane is anything but mild, as Ireland is realising the impact of Storm Ophelia.

With much of Ireland remaining indoors today (16 October) thanks to the arrival of Storm Ophelia, questions are being asked as to the nature of a storm unlike any seen in a number of decades.

While the word ‘hurricane’ has been mentioned quite often in Irish media, Met Éireann announced this morning that Ophelia has been downgraded to an ‘ex-hurricane’.

This does not mean that the danger has passed, not by any stretch of the imagination, but its strength has been somewhat diminished after travelling across the Atlantic Ocean.

The confirmation of Ophelia becoming an ex-hurricane was first revealed by the National Hurricane Center based in the US at around 3am IST.

It means that what we consider to be the core characteristics of a hurricane are not present in Ophelia. This includes the famous eye that, while appearing eerily calm to those within it, hides the brute force of the hurricane winds that surround it.

Unlike the warm waters off the Gulf of Mexico or off the south-east coast of the US, Ireland and the UK are in a much safer position as our seas are too cold to sustain hurricane-strength storms for very long.

For example, Ireland’s current average ocean temperature sits at just over 13C, which puts it far below the necessary minimum ocean temperature of 26C to sustain a hurricane.

Such downgrading of storms are not that uncommon, with Hurricane Irma earlier this year being one example.

Sting jet?

Ophelia is currently categorised as a category 1 storm having achieved its fastest wind speed of 176kph at Fastnet Rock, 6.5km off the coast of Cork. This enormous speed is likely an indicator of a ‘sting jet’, a highly dangerous phenomenon associated with rapidly developing mid-level storms.

As the UK Met Office highlighted the other day, the name originates from its scorpion tail-like shape seen in satellite imagery as it wraps around the centre of an area of low pressure.

As the rain falls into the descending air, it cools further, rapidly accelerating wind speeds.

All of these factors make it one of the strongest storms to have ever hit Ireland in around half a century.

To keep track of where the storm’s winds are strongest and any other meteorological data, you can check out some of these online resources we highlighted earlier.

Colm Gorey was a senior journalist with Silicon Republic