19 September 2018
I did a little research on just how incredibly uncomfortable the summer of 2018 has been in the Northeastern U.S. and the numbers are astounding. The graphs below show how many hours the dew point was above a certain level in different time periods. All months means total hours since Jan. 1st through Sept. 18th 2018.
For those who are shaky on what the dew point is, let me put it this way. Dew point is what you THINK the relative humidity is. Relative humidity is relatively worthless as a judge of how wet or muggy the air feels, but dew point is perfect. The higher the dew point the more water vapor in the air.
This is NOT true of relative humidity. Forget relative humidity unless you use a line to dry clothes, or farm a field! There are actually many ways we meteorologists measure atmospheric moisture and a good discussion about them is here.
If that’s too much for you, here’s a good scale:
Dew point below 45 is dry and crisp air in the fall.
Dew point below 20 is Las Vegas/desert dry.
Dew point over 60 is humid.
Dew point over 70 is muggy
Dew point over 75 is very muggy
A Dew point over 80 means you’re either in the Persian Gulf, Key West, or standing in the queue for Dumbo at Disney World in August (technically the hottest spot on Earth in my mind).
Now that we have that down, the graphs below will make sense, and make you sweat. Oh, when you add greenhouse gases to the atmosphere, the oceans warm and the amount of water vapor in the air goes up.
The high dew points have kept the nights very warm through September. Here in Maryland where I live, Salisbury’s minimum temperature average so far in September is hottest on record.
Why so humid? See the the ocean. The map below shows not temperature but how far above average the temperature is in the Atlantic. This had a direct impact on the catastrophe in North Carolina last week as well.
For those that are really ready for some cooler and drier fall weather, you may need to wait another ten days. Strong indications are that the pattern will change around the end of the month. I myself am taking no chances and am headed to the land of stormy skies and gales (London) in early October. Stormy skies and gales are just some of my favorite things!
FYI the first real fall storm in the Atlantic is headed to the UK and Ireland this morning. You can hear about it on the famous shipping forecast on BBC Radio 4. Tonight’s edition covering the big storm is here.