What causes these periodic high-pressure blobs along the west coast of South America?

Question

I was looking through the Weatherbug atmospheric pressure map around 8:30 am ET on Oct 26 2021, and noticed this chain of small high pressure blobs along the west coast of South America. It was also present around a few days prior, around 8 am ET on Oct 23 2021.

I looked up the geography and major winds in the region and noticed

1. This is a region with mountains nearly along the coast
2. There are northbound trade winds that roughly hug the coast

I then looked for a similar effect in other places with similar conditions and found this other high pressure chain along the southwest edge of Indonesia (screenshot from around 12 pm ET on Oct 26 2021):

There's a coast-hugging wind along this region (this one eastbound), and as far as I can tell the mountains here are lower than the ones in South America. I've noticed the high pressure blobs seem smaller and have a lower maximum pressure, though this may be due to it being night there when I checked.

With all that background information, my questions are: what, physically, causes this effect? Are these high-pressure chains semi-permanent, and if so, do the individual blobs tend to stay in the same place or shift around a bit?

My background's in physics rather than meteorology so I'd love an answer that describes the physical phenomena or "follows the wind" as it encounters mountains and valleys. Bonus points for descriptions of how e.g. mountain spacing, mountain height, wind speed, etc may affect blob spacing and pressure magnitude.

Answer 1

It's really not clear from their website what data source those maps are showing. They could be derived purely from surface observations, purely from model output, some atmospheric analysis combination of the two, or something else.

When I see such neat bullseyes like that, it's normally a warning sign that someone is trying to do too much with a sparse dataset by interpolating low numbers of data points over large distances. I looked into quite a few of the blobs on your maps and they were all located in remote, sparsely populated regions such as mountains, national parks or extensive forests, often with an airfield or research station nearby where there could be an isolated weather station. There are similar oddities in their wind speed maps, which mainly show blobs centered on towns and cities where weather stations are likely to be located:

Note that over the US the wind speed map is broadly in line with the ECMWF analysis, albeit with lots of artificial blobbiness because of whatever sampling and interpolating they're doing.

I suspect that the surface pressure maps are made even worse because they're surface pressure rather than sea level pressure, so the sparse samples can reflect altitude more than transient weather. That would lead to the major features that you've highlighted being persistent in time.

The bottom line is that I think the features that you're seeing are artifacts of a bad methodology rather than a physical phenomenon.