The Meteorological autumn arrives on Sunday and the GEFS is showing it will arrive on time.
This graph shows the temperature at 1,500 metre 850 hpa. We use this height because it does not really matter if its daytime or night time and there is little effect from reflective surfaces from the earth. The thick black line is the average 30 year temperature. The bottom of the graph is rainfall. All the thin different colour lines are what the members think will happen. The closer the lines are the closer the agreement is with the members that make up the gefs.
So looking at this graph you can see the temperature will take a sharp drop on the first of September. I expect the temperature to fall to around a daytime maximum of just 16 centigrade. It looks like there will be a brief recovery round the 3rd of September for two or three day’s. Precipitation wise it looks like there will be showers. Temperatures looks like they will increase a little from the 8th onwards but confidence is low most members soon bring the temperatures down again.
This is the air pressure graph from the GEFS. Overall the air pressure looks like it will be high with just a brief sharp drop the very start of the month recovering to above 1020 hpa. This tells me that the centre of the high pressure will be off the North Western side of the UK and this will bring our wind direction from a north-westerly direction hence the reason for cooler temperature and some showers.
Early September will be cool with below average temperatures and showers.