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Q&A: Relative humidity too imprecise for weather forecasters

The relative humidity doesn’t always accurately describe how it may feel outside.


The relative humidity doesn’t always accurately describe how it may feel outside.

Relative humidity too imprecise

Humidity is no longer provided in the weather forecasts. Why?

We turned to our TV partners, Bay News 9, for this answer. Chief meteorologist Mike Clay writes:

"Giving the 'relative humidity' has little value. It is always 'relative' to the temperature.

"For example, the RH is almost always 100 percent in the morning. The temperature could be 40 and the dew point 39, making the relative humidity 96 percent, but the air is dry.

"On a summer afternoon, the temperature could be 93, the dew point 68, making the relative humidity 42 percent, but it is uncomfortable.

"It is impossible to give one humidity value for the day since it changes hourly based on the temperature. On TV, we often show the dew points. This is what meteorologists use to judge the amount of moisture in the air. The dew point is a constant value.

"When we write the weather story, we try to point out very humid/muggy weather or very dry air. We might say something like: 'It will be a hot and humid day today, but drier air arrives tomorrow to make it feel more comfortable.' This is more valuable than showing the relative humidity at 100 percent every morning and 40 percent every afternoon."

Cat 5 hurricane hit Keys in 1935

I know that the only hurricane to hit this area was 1921. The Times edition about hurricanes stated that in 1935 a hurricane hit the bay area. To settle an argument, what was the name?

The decision to name hurricanes was made in 1953 by the National Hurricane Center. Before then storms were simply numbered as they occurred. The NHC's reasoning was that a name allowed it and the public to better identify individual systems. The NHC used female names only until 1979, when it began alternating men's and women's names.

The storm names, which are now maintained and updated by an international committee of the United Nations' World Meteorological Organization, are assigned for a six-year cycle, then the cycle is repeated unless a storm name is retired.

This season's names are Alex, Bonnie, Colin, Danielle, Earl, Fiona, Gaston, Hermine, Igor, Julia, Karl, Lisa, Matthew, Nicole, Otto, Paula, Richard, Shary, Tomas, Virginie and Walter.

The 1921 storm was the only major one to directly hit the Tampa Bay area. But many other storms have come close enough to have an impact in our area.

One of those was mentioned by Bay News 9 meteorologist Brian McClure in a story in the 2010 Hurricane Guide. The Labor Day 1935 storm (also known as Storm #2) hit the upper Keys as a Category 5 hurricane on Sept. 2 and then moved up the west coast of Florida before weakening and hitting land again Sept. 4 in the Cedar Key area. It caused some flooding and damage in our area.

Q&A: Relative humidity too imprecise for weather forecasters 06/20/10 [Last modified: Sunday, June 20, 2010 4:30am]
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