I had to check that I wasn’t seeing things when I first looked at the ECMWF hi-res model for next weekend across IONA. For a moment I thought I’d downloaded the images from the wxcharts.com site in the wrong order, but on checking they were correct, and I assume wxcharts.com got it right at their end as well. A low comes in from the southwest approaches next Friday (982 hPa) deepening quickly as it tracks in a generally westerly direction towards London by 00 UTC on Saturday (963 hPa). The intense low, or should that be storm Aiden, because if this comes off it just has to be named, then turns sharply left and heads northward up the east coast of England (952 hPa), before turning left again and heading northwest across the outer Hebrides to finish back in the northwest Atlantic (964 hPa). The retrograde track of this low if it comes to pass is really quite unusual even more so given that the low is so intense.
I tried to find something about retrograde lows on the internet – if that’s what this low actually is – and found this article on Jeff Haby’s very intersting weather site:-
To retrograde means to move in the opposite direction of what is climatologically typical. In the middle latitudes, pressure systems tend to move generally from the west toward the east. This is the same general direction that the jet stream winds move. A retrograding low is most likely to occur when the upper level steering winds are weak (jet stream weak and displaced closer to the pole). This lack of steering can not only contribute to retrograde motion but it can also result in pressure systems that move slowly or stall for several days. When pressure systems stall or nearly stall it is referred to as a blocking pattern. Both high and low pressure systems can retrograde or stall.Jeff Haby
The ECMWF model is one of the most reliable and trusted NWP models around, but in the last month it has thrown a few curved balls and this could be just another one.