Storm Betty UK: yellow warnings issued across the UK as half a month of rain to fall today - how long will it last?

The south of England could see more than half a month's rain and thunderstorms as the weather on Friday (18 August) takes a turn to unsettled conditions. 

Storm Betty, named by Met Eireann, comes after just a few days of sunshine. 

The Met Office has issued a weather warning for the south of England, which could see around 30mm to 40mm of rain in just six hours. Over the entire month of August, the southeast usually sees 63mm. 

The Met's warning covers large parts of the South and West Midlands, as well as London and the Solent area. Birmingham will also feel the effects - all between 6am and midday on Friday (18 August). 

A second thunderstorm warning has been announced covering the East Midlands, the east and south-east of England and London will come into effect at 8pm on Friday and last until 5am on Saturday.

Heavy and thundery rain will spread across many parts of the UK on Friday night with the potential for some large hail, especially in East Anglia, Kent and East Sussex.

Significant rainfall is also expected in Northern Ireland as a weather warning will be in place from 9pm on Friday to 6am on Saturday. Around a months' worth of rain - 40mm-80mm - could fall in hilly areas and around 15mm-25mm elsewhere.

Storm Betty is also expected to bring strong wind gusts in excess of 60mph, and more widely around 40-50 mph have led to a yellow warning being issued in the northern and western coastal areas of Wales. 

Met Office meteorologist Aidan McGivern said: “There’s an area of low pressure to the west. This will orientate with the high pressure and will waft in some warmer air from the south in the next few days. 

“Another area of low-pressure heads towards the UK at the start of Friday. The instability in the atmosphere will create a line of showers or even some thunderstorms and there could be some heavy downpours moving through central parts of the UK, though there is some uncertainty on the distribution.

“Where we do get some breaks in the cloud on Friday, it will still be a fairly warm day, though temperatures won’t be exceptional, and it will feel quite humid because of this southerly airflow.”

Met Office deputy chief meteorologist Steven Keates added: “The main event arrives during Friday evening, with the potential for intense thunderstorms to break out over parts of England, bringing a lot of rain in a short period of time, along with the risk of hail and frequent lightning.

“At the same time heavy rain, initially arriving into the southwest, will fairly steadily move northeast, potentially bringing some substantial rainfall totals to parts of Northern Ireland and eastern Scotland in particular.”

Five day Met Office outlook

Friday: Bands of heavy and thundery rain will push northeastwards throughout today. Dry, bright and feeling warm either side of this. Further heavy rain moving into the southwest later. Increasingly windy.

Friday night: Remaining cloudy and rather windy tonight as outbreaks of heavy rain and thunderstorms push northeast. Turning drier from the southwest by dawn. Feeling very humid.

Saturday: A rather cloudy and blustery start with outbreaks of heavy rain continuing northeastwards. Sunshine and showers continuing in the northwest, becoming drier and brighter for many though. Feeling warm.

Outlook for Sunday to Tuesday: Less humid on Sunday with scattered showers becoming increasingly isolated to the northwest by Monday. Perhaps cloudier on Tuesday, although remaining dry for most. Feeling warm, especially in the southeast.