Updated 28th July
Covering the period 4th August - 26th August
Changeable, but rather warm in central and eastern parts of the country, thanks to frequent southerly and south-westerly winds. Fine spells are most likely during the second week of August.
Due to southerly winds blowing more frequently than usual, temperatures will generally be above the 1981-2010 average, though there will be a west-east gradient, with positive anomalies of 0.5C or less in Northern Ireland, but possibly reaching 1.5 to 2.0C in East Anglia with eastern Britain generally more than 1.0C above.
Rainfall totals are likely to come out slightly above average in western parts of Britain and close to average in the east, but with significant local variations, especially in the east, due to localised heavy thundery downpours.
I expect sunshine totals to be slightly below average in western Scotland and Northern Ireland, but above average in eastern Scotland and in central and eastern England, with near-average totals elsewhere.
Monday Monday 4th August - Sunday 10th August
This will be a generally unsettled period but lowest pressure will often be centred to the west of the British Isles, and as a result, southerly winds will blow more frequently than usual, so it is likely to be warmer than average, particularly in eastern parts of the country, and as has been a common theme this summer, the jet stream is unlikely to be very strong so we are unlikely to be seeing a rapid succession of frontal systems heading eastwards across the country.
The weather is likely to be most unsettled between the 4th and 7th with low pressure dominant to the west of Scotland, bringing two or three belts of persistent frontal rain eastwards across the country, with brighter showery periods in between the rain belts, and some of the showers will be heavy and thundery. In general, temperatures will be near or slightly below average in Ireland and western Scotland but are likely to be slightly above average in eastern parts of Britain thanks to southerly and south-westerly winds. Between the 8th and 10th, high pressure is likely to build to the south and east of the British Isles with low pressure becoming displaced further to the west and this will result in longer warm sunny periods for eastern and southern parts of Britain. It will remain changeable for most of Scotland, Northern Ireland and north-western England, but even here some drier sunnier interludes are likely.
Temperatures will be slightly above the long-term normal in central, eastern and southern England and also in eastern Scotland, but will be near or slightly below in the west of Scotland and in Northern Ireland, closer to the centre of the low pressure. Rainfall totals are expected to be above normal in most parts of the country, but with significant local variations, especially in eastern Britain, because much of the rainfall is likely to be showery and thundery in nature. Sunshine totals may fall a little below normal in western Britain but are likely to be near or slightly above normal in eastern Britain.
Monday 11th August - Sunday 17th August
There remains a strong signal for cyclonic conditions but with lowest pressure centred to the west of the British Isles, meaning that southerly winds will continue to blow more frequently than usual, so it is likely to be warmer than average, particularly in the east of the country. Relatively settled weather is most likely early in the period (11th-14th) as some ridges of high pressure will head north-eastwards from the Azores and move across into central and western parts of Europe. There will thus be significant spells of warm dry sunny weather for central, eastern and southern England and also probably in eastern Scotland, but the west and north-west of the British Isles are more likely to hold onto changeable conditions with some bands of rain or showers, though there will be some drier sunnier interludes in these regions too. Changeable conditions are likely to become established more widely between the 15th and 17th as the main centre of low pressure heads eastwards towards the British Isles again, but eastern, central and southern England may hold onto relatively dry sunny conditions. The southerly winds may also bring thundery outbreaks northwards from continental Europe on occasion.
Temperatures are likely to rise more significantly above the seasonal norm in most eastern parts of Britain during this period, probably by a couple of degrees Celsius, but they are likely to be only slightly above normal in Northern Ireland, Wales and the west of Scotland. Rainfall is expected to be close to or slightly below normal, but again significant local variations are expected due to localised thundery downpours, especially in eastern parts of the country. Sunshine totals are likely to be close to normal in western parts of Britain but above normal in central and eastern England and in eastern Scotland.
Rest of the month
Monday 18th August - Tuesday August 26th
The frequency of cloudy, wet and breezy weather is likely to increase during this period, particularly in the west of the country, as we will start to see deeper low pressure systems heading in from the Atlantic, but there remains a signal for more frequent southerly winds than usual, so eastern parts of the country are likely to remain warmer than average for the time of year. Eastern counties are also the most likely to have significant drier brighter interludes in between the belts of rain or showers, as ridges of high pressure will occasionally head north-eastwards into central Europe, breaking off from the Azores High.
As a result this period is likely to be cloudier and wetter than average in the west of the British Isles, but with eastern parts having close to average sunshine and rainfall totals. Temperatures will be close to average in the western half of the country but are likely to be slightly above average in the eastern half of the country.