Updated 19th September
Covering the period 26th September - 18th October
Warm and changeable until early October, then dry, with variable amounts of cloud, but some regions notably sunny
Mean temperatures will be about 1C above the 1981-2010 long-term average across most of the country, with significant positive anomalies early in the period, but some colder nights later in the period under high pressure and with lighter winds.
Rainfall totals will be below normal everywhere, but only slightly below normal in the west of Scotland and in Northern Ireland. Some eastern, southern and south-western areas may only record about half of the normal rainfall, though exceptionally low rainfall totals are unlikely, with the high pressure likely to be intermittent rather than consistently dominant.
Sunshine totals will be close to normal in Northern Ireland, but mostly above normal elsewhere, especially in Wales and western parts of England.
Monday 26th September - Sunday 2nd October
Changeable west to south-westerlies will dominate during this week but with a growing tendency for high pressure to ridge into the east and south, keeping weather systems more confined to north-western Britain.
Strong west to south-westerly winds will dominate between the 26th and 28th September. The 26th will be a cloudy and humid day, with heavy persistent rain over much of Scotland, Northern Ireland and north-west England. Most of the rest of England, together with central and southern Wales, will have a mostly dry day but rain will spread from the north-west late in the day. Rain is expected to linger over southern and central England and south Wales on the 27th, with cooler brighter showery weather further north, the majority of the showers over and to the west of high ground. The 28th will be similar to the 26th, with cloudy but mostly dry weather in the south and rain affecting central and western Scotland, north-west England, north Wales and Northern Ireland. Winds may reach gale force in many exposed parts of Scotland. Temperatures will mostly be near normal by day and above normal by night.
However, between the 29th September and the 2nd October, high pressure will frequently ridge into the southern half of Britain bringing much more settled conditions. There is uncertainty over the exact timings of weather systems, but Scotland and Northern Ireland will be affected by rain belts at times, but with the high pressure ridging right up to the north of Scotland in between the systems, bringing interludes of dry bright weather. For England and Wales, although there will be some cloudier intervals associated with tropical maritime air masses, it will generally be sunnier as well as drier than average for the time of year. Temperatures will mostly be close to the seasonal norm, with warm days offset by cool nights, but the tropical maritime incursions will bring above-average night time temperatures.
Mean temperatures will typically be about 2C above the 1981-2010 long-term average, due to the warmth of the tropical maritime south-westerly incursions, and mostly near normal at other times.
Rainfall totals will generally be above normal in western Scotland and close to normal over much of Northern Ireland, central and eastern Scotland and north-western England, but it will be drier than average over most of England and Wales.
Sunshine totals will tend to be below normal early in the week but then becoming more plentiful later in the week. Overall, most parts of the UK will have close to average sunshine but Wales and the west and south of England will be rather sunny, while Northern Ireland will be duller than normal.
Monday 3rd October - Sunday 9th October
This will be a generally anticyclonic week but with low pressure systems occasionally bringing frontal systems mainly to the north, especially around midweek (6th/7th). High pressure will usually be centred over or just to the south of the British Isles. Again, some imports of moist tropical maritime air will bring cloudier conditions at times, but for the majority of the time it will be quite sunny for most of the country. Winds will predominantly be westerly in the north, and variable in the south, closer to the centre of the high pressure.
Temperatures will be closer to normal this week due to some cool nights, with the mean temperature generally 0 to 1C above the 1981-2010 average, though more than 1C above in eastern Scotland, and fractionally below average in parts of the south-west. Rainfall totals are expected to be below normal everywhere, though probably not exceptionally so, due to a relatively unsettled interlude midweek. Sunshine totals will generally be above average; even in the north and west of Scotland there will be significant drier brighter intervals in between the rain belts.
Rest of the month
Monday 10th October - Tuesday 18th October
Prevailing signals for this period suggest that high pressure will remain dominant for most of the time, with a greater continental influence than earlier, with winds often blowing from a southerly or easterly direction, especially across southern Britain. Temperatures are expected to be very close to the long-term normal, though rather above in northern Scotland, with rainfall totals below normal, especially so in western Britain. It will generally be sunnier than average in the west but sunshine anomalies are more uncertain in the east, due to the potential for cloud to head in off the North Sea at times. Overall close to average sunshine is most likely in the east.