August 26, 2010 - Dewpoint Explained & Tropics Update

By: Mallory Brooke
By: Mallory Brooke

I received some questions on my last blog, so I'm answering them today! Read all about dewpoint along with a quick tropics update in today's blog

It's Thursday...that means one day closer to Friday (and a beautiful weekend)! Ok, back to business.

I received two great questions on my blog Tuesday.

First, I'll answer Ronnie's question: Could you explain what the dew point is?

The official definition from the American Meteorological Society is "The temperature to which a given air parcel must be cooled at constant pressure and constant water vapor content in order for saturation to occur."

A more simple way to think of it is the amount of moisture in the air for a given temperature. The higher the temperature, the moisture the air can hold. That's the reason we feel so much more moisture in the summer than in the winter. 

The closer the dewpoint is to the temperature, the more moisture is in the air and the closer the air is to saturation. With a temperature of 85 and a dewpoint of 75, it feels incredibly uncomfortable outside. A temperature of 85 and a dewpoint of 55 is comfortable. However, in the winter, a temperature of 35 and a dewpoint of 30 doesn't feel humid. Winter time comes down to "which day feels more dry" and "how many bottles of lotion do I need today"?

I hope that answered your question Ronnie!

Onto Eddie's question: Also does the dew point determine humidity or does humidity determine the dew point?

Eddie, dewpoint determines humidity. We consider this a "relative" humidity, because it's "relative" to the temperature. Given a temperature and dewpoint, we can calculate the humidity using an equation called the Clausius-Clapeyron equation. I won't go through the whole equation here (it still hurts my head and brings me back to dynamics class), unless someone *really* wants me to.

Please feel free to ask any questions about my blog or on blog topics in the comments section. I'll answer them as soon as I can in the next blog.

Finally a tropics update for us. At 11am Thursday morning, Hurricane Danielle remains a Category 2 storm with a heading to the east of Bermuda. This leaves Bermuda in good (relatively) spot because the most intense portion of hurricane is on the eastern side. Tropical Storm Earl continues on a westerly path with winds of 45 mph. He's expected to strengthen to hurricane status by the weekend.

I'll have another update on the tropics Friday. Blogs will be on hold for a bit as I go on vacation next week, but will be back on Labor Day!



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