Ireland is about to see a sudden change in weather conditions over the coming days especially this weekend when a very strong and powerful jet stream strengthens with areas of low pressure developing in the north Atlantic and been steered towards west and northwest Europe close to Ireland and the UK.

An area of low pressure will pass of the northwest of Ireland and to the south of Iceland on Friday night and Saturday and bring heavy rainfall and strong winds.

HEAVY RAINFALL AND STORM FORCE WINDS ON FRIDAY NIGHT AND SATURDAY

As the Atlantic low passes between Ireland and Iceland it will see bands of rainfall sweep west to east across Ireland on Friday night and Saturday morning with very heavy fall in places with the risk of thunder which will lead to some spot or localised flooding along with the risk of river flooding especially due to how saturated the ground is at present with all the rain so far this week. There could be a further 30mm to 40mm of rainfall across some southwestern, western and northwestern counties between Friday night and Saturday morning. Weather warnings will be possibly issued for some counties for this time period for rainfall.

The latest model runs from the ECMWF suggest we may even see this Atlantic low be given a storm name but that will depend on the current model runs over the next 24 hours,

On Friday night southwest winds will strengthen across Atlantic coastal counties and become gusty to strong. After midnight into Saturday morning winds will be strong across much of Ireland winds gusting between 90 and 110km/h.

Stronger winds may occur across Donegal, Mayo, Galway, Clare, Limerick and Kerry for a time on Saturday morning with winds gusting between 100 and 120km/h. A Orange warning may be issued for strong winds but at present this warning would be under the lower end of the scale for a Orange warning. Strongest winds in these areas will be across exposed coastal parts and over high ground

Strong wind combined with high tides could also lead to some coastal or tidal flooding in places with sea walls been over toppled.

Southwesterly winds will ease for many areas on Saturday afternoon and evening and become gusty, however across Atlantic coastal counties winds will remain strong especially across coastal areas.

Sunday will be showery day across west Ulster, Connacht and west Munster where there will be some heavy showers but drier across eastern areas where the best of any sunshine will be with gusty westerly winds.

A RISK OF A VERY STRONG ATLANTIC LOW NEXT WEEK WHICH COULD BREAK RECORDS

At present in the tropical Atlantic we have Hurricane Epsilon which rapidly intensify this afternoon and is now a category 3 hurricane on the Saffir-Simpson Hurricane Wind Scale. Hurricane Epsilon was located over the central Atlantic Ocean about 340 miles (545 km) east-southeast of Bermuda.

Hurricane Epsilon is Currently moving towards the northwest but on Friday will take a turn to the east and start moving northeast across the Atlantic over the weekend and get caught up in the strong Atlantic jet stream. By Monday Epsilon will undergo the transition from a Hurricane into a post tropical storm but will undergo rapid cyclogenesis with a very dramatic pressure drop within a 24 hour period on Tuesday with some high resolution models suggesting the low central pressure falling as low as 915hPa as can be seen on the chart below.

The below chart is something in the weather world we call a ensemble forecast or chart which helps us forecast where there is uncertainty within the forecast. An ensemble weather forecast is a set of forecasts that present the range of future weather possibilities. Multiple simulations are run, each with a slight variation of its initial conditions and with slightly perturbed weather models. These variations represent the inevitable uncertainty in the initial conditions and approximations in the models. They produce a range of possible weather conditions.

By generating a range of possible outcomes, the method can show how likely different scenarios are in the days ahead, and how long into the future the forecasts are useful. The smaller the range of predicted outcomes, the ‘sharper’ the forecast is said to be. Good ensemble forecasts are not just as sharp as possible but also reliable. If a reliable forecast says that there is a 70% chance of top temperatures rising above a certain threshold, then in 70% of cases when such a forecast is made temperatures will indeed rise above that threshold.

Above you will see the ensemble chart from the ECMWF for the possible outcome for the next week and what the chances of Ireland seen a impact from then which will be a ex Hurricane Epsilon which will have become a very powerful Atlantic storm. above shows the ensemble spread showing the storm passing close or even near Ireland but a better understanding of the system will be known over this weekend.

Possible time frame and effects Ireland may feel from this powerful low will be Tuesday the 27th October.

Hurricane Epsilon will also bring the risk of very high seas and coastal flooding next week and combined with strong winds it will add to the dangers and risks with the very deep low creating a large swell as it moves eastwards across the Atlantic.

The large swell can be seen on the image below

Just to put this storm in comparison the lowest area of pressure ever recorded in the north Atlantic was on the 2nd December 1929 at Stórhöfði peninsula, Heimaey southwest Iceland 920 hPa. The Ecmwf model has next weeks storm as low as 915 hPa but its early days and will have to be watched.

If a storm with such a low central pressure was to move close or over Ireland it would causes devastating damage. The closer you are to the center of the low pressure the tighter the isobars and stronger and more severe winds will be. As mentioned above the latest model runs thankfully keep the storm well out sea but further changes are likely by next week.

I will have further updates over the end of this week and this weekend on the two storm risks with the first storm on Saturday and then next week around Tuesday possibly into Wednesday.

Kenneth Mc Donagh from the Donegal Weather Channel

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