Weather often changes for more than a year or more downwind of large volcanic eruptions

For example, an Iceland Volcano created the French Revolution because pyroclastic glass and shards blocked the sun from Iceland when they traveled over France. So, when people starved and only the aristocracy got food the poor invented the guillotine and chopped off the heads of any aristocrats that stayed in France. So, this wiped out the aristocracy of France in the 1790s then.

It would be difficult to see what changes happen from Mauna Loa or Mauna Kea eruptions because most of the prevailing winds might be out to sea in various directions but sometimes what they call the VOG (or Volcanic Fog) common when you are downwind of one of Hawaiis eruptions comes to where you are on one of the other islands or on the big Island of Hawaii where they usually generate.

But, When Mt. St. Helens blew up in 1980 on March 27th 1980 I was living in the Mt. Shasta area with my family and young children at that time and was buying 2 1/2 acres which I built a house on.And I noticed that the weather was 10 to 20 degrees cooler year around and that it rained and snowed a lot more for around 2 to 3 years after the eruption and this was true from Seattle to maybe Sacramento and San Francisco where the weather changed a lot for 2 to 3 years. The other strange thing was that there were very unusual sunsets with Orange and Purple and  Green and Blue a lot which I have never seen anywhere else again since those 2 to 3 years from 1980 to 1983 in Mt. Shasta caused by the Mt. St. Helens eruption in March of 1980.

However, most of the time the weather changes are a cooling of 10 to 20 degrees if it is a large eruption from a volcano. But I don't know how you would measure something like this on Hawaii because most of the time the VOG from the volcano is going out to sea and likely not going to the other islands.

However, you likely could monitor what it does to the Big island (Hawaii weather).