The extended range forecast, which includes the monthly and seasonal forecasts, can at times provide an insight into weather patterns in the months ahead. However, they should not be used for specific planning purposes as they have generally low skill compared with the 10-day forecast. This is because forecasts beyond one week become increasingly uncertain due to the chaotic nature of the atmosphere. Further information can be found here Monthly and seasonal forecast explained.
Images: Shutterstock/gabriel12. Met Éireann HQ during Storm Emma 2018
MONTHLY FORECAST, ISSUED FRIDAY 29 AUGUST 2025
Week 1 (Monday 01 September to Sunday 07 September)
Low pressure is set to continue dominating our weather, bringing in unsettled conditions from the Atlantic. It will be wetter than average across the country for the time of year, with the most rainfall forecast for the southwest, west and northwest. Temperatures will be average for the time of year.
Week 2 (Monday 08 September to Sunday 14 September)
With confidence becoming lower for week 2, there is a small signal for mean sea level pressure to increase. Rainfall amounts are forecast to be below average for the time of year, while temperatures are forecast to be close to average or slightly above.
Week 3 (Monday 15 September to Sunday 21 September)
While uncertainty is increasing in the forecast for week 3, it’s a similar story to the previous week with a slight signal for high pressure to have more of an influence. Rainfall amounts are expected to be average for the time of year, although possibly slightly below average in the west, northwest and north. Temperatures are forecast to be average or very slightly above for the time of year.
Week 4 (Monday 22 September to Sunday 28 September)
While forecast confidence is low for week 4, there is a slight signal for low pressure to dominate. Rainfall amounts are forecast to be slightly higher than average while temperatures are forecast to be average or very slightly above.
Seasonal Outlook for September October November (SON)
The signal from the C3S seasonal models for Ireland during the September October November (SON) period is for above average temperatures, with average rainfall overall.
Mean temperatures during SON are signalled to be above average overall. Temperatures are likely to trend between 0.5 and 1.0°C above average over the three-month period.
The rainfall forecast is less certain, with the potential for both wetter and drier periods through the Autumn season. There is however a higher signal for drier periods in October at times.
The sea surface temperatures around Irish coasts are expected to be above average during SON, trending 0.5 to 2.0°C higher than normal.