This is my four week outlook using the JMA from the Japanese Met Agency from September 21st to October 18th. This is not a forecast but a general outlook. I have added the images together, rotated them and add a redline so you can see the UK. Blue colours is low pressure troughs and Oranges is high pressure ridges.
Week 1 21st September to 27th.
This period is showing low pressure across the Atlantic and over the UK with high pressure to the South of the UK.
During this period we will see some unsettled conditions bringing some wet and sometimes windy weather. West and Northern UK will see the wettest weather with Southern England seeing the least rainfall.
Week 2 28th September to 4th October.
During this period, low pressure will be over the Northern parts of the UK with High pressure building from the South moving towards central parts of the UK.
We will see some showery conditions, with Northern UK seeing some wet weather. This period could be quite changeable.
Week 3-4 4th October to 18th.
This period will see high pressure ridge building in the Atlantic close to the West coast UK. It will become drier but temperatures will be on the cool side.