Irish Sea shaped isobar

Gwynston

Checking the BBC Weather pages today, this predicted pressure map for Tuesday caught my eye:



The high pressure peak centered between Ireland and Britain seems to almost exactly match the outline of the Irish Sea!

Is it usual that pressure level boundaries follow coastlines? Or was this just some lazy BBC Weather (or Met Office?) intern who couldn't be bothered plotting the isobar line accurately and just followed the outline already in front of them?

Supercell

At a wild guess I'd speculate the cooler more dense air over the sea area in a slack airflow is enough to cause a slight pressure differential when compared to the nearby warmer landmasses of Britain and Ireland? Kind of like the Siberian high that forms every winter.

Gwynston

Yeah, looking at it again, there are a few isobars on that pic that follow coastlines pretty closely:

- The High that covers most of the North and Baltic Seas
- The north-west of Africa