Thursday 18 October 2018

Explainer: 'Sting jets', 'ex-hurricane' and 'jet streams' - what they mean and how they're going to impact Ireland

Sandbags at the ready in Clontarf this morning for Storm Ophelia
Sandbags at the ready in Clontarf this morning for Storm Ophelia
Independent.ie Newsdesk

Independent.ie Newsdesk

The US National Hurricane Centre said Ophelia has now become an "ex-hurricane", but while this sounds less serious, the Florida-based centre has warned the storm is still on course to have a huge impact on Ireland.

Some of the hurricane terminology being used by weather forecasters will not have been heard by many Irish people before, so here they are explained.

What is an ex-hurricane?

Hurricanes and tropical storms that form in the Atlantic tend to not be considered hurricanes by the time they reach Ireland and the UK, having transitioned into what are known as post-tropical storms.

This means the traditional attributes of a hurricane — such as the eye containing a core of hurricane force winds — are very unlikely to be present.

How does a hurricane become an 'ex-hurricane'?

As the waters around Ireland and the UK are much too cold to sustain a tropical weather system, hurricanes are often downgraded by the time they reach here.

Ophelia was over sea surface temperatures of around 77 degrees over the past two days, which is barely warm enough for a tropical weather system. When it hits Ireland, it will be over water temperatures of around 60 degrees, which is too cold for a tropical system, according to the Met Office.

Does that mean it will cause less damage?

While an ex-hurricane may not be as powerful as a hurricane, they still cause "significant" damage.

Heavy rain will batter the country and strong wind gusts will hit the west coast of Ireland particularly hard.

It is "the strongest an Atlantic hurricane has been this far east this late in a calendar year on record," according to Phil Klotzbach, tropical weather expert at Colorado State University.

While the US National Hurricane Center lowered the storm's status to a Category 1, Met Éireann warned it is expected to be the most severe weather event to hit the island of Ireland in over 50 years and a status red alert wind warning has been issued for the entire country.

What's a 'sting jet'?

The Met Office describes a sting jet as a "meteorological phenomenon" that is responsible for causing some of the most damaging winds in extratropical cyclones.

Sting jets get their name from the hooked tail of clouds that spawn the fierce gusts and the clouds resemble a scorpion's tail, according to the Met Office.

Sting jets can accelerate to more than 100km/h if they hit over land.

What is a 'jet stream'?

The jet stream is an area of strong winds high in the sky that helps to guide storms and separate air masses.

Jet streams are found 9-16 km above the surface of the Earth, just below the tropopause, and can reach speeds of 200 km/hr.

How is Ophelia affecting you today? Send your comments and pictures to contact@independent.ie, if it is safe to do so.

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