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Barometric Pressure and Hurricanes

Barometric Pressure and Hurricanes

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What is the difference between barometric pressure that effects our weather and millibars that are in a hurricane?

Jim M. **********************************************************

In the subject of this email Jim also asked what a millibar was so we'll cover that too. First of all, a millibar is just a unit we use to measure pressure just like inches of mercury. The millibar is a function of the bar, another unit of pressure related to Pascals or atmospheres. We usually use inches of mercury for most public weather forecasts but meteorologists work mostly in millibars, it's much easier the scale is simple to use when we contour our weather maps.

If you really want to get into the nitty gritty, inch of mercury equals 33.86 millibars. You can either have fun with calculations or run some tables to do it for you. Bottom line, millibar is a unit of pressure.

Hurricanes have very low pressures. The lower the pressure the more intense the storm is considered. The normal sea level pressure in the US is 1013.25 mb a hurricane's pressure drops much lower. The lowest hurricane pressure on record was not long ago, Hurricane Wilma in 2005 had a central pressure of 882 mb!!!! That is some serious low pressure. The max winds with Wilma were 175 mph. The Labor Day hurricane of 1935 had a low pressure of 892 mb and winds of 200 mph! While this hurricane had stronger winds, the lowest pressure wins out on the intensity scale.

Our lowest pressure here in SLC was the tax day storm in 2002, April 15th the pressure dropped to 29.00 inches of mercury. That equates to about 982 millibars! That's low. In the winter with big areas of high pressure we can have pressures as high as 1045 mb. The highest ever was about 1052.8 mb here in SLC.

If you want to brush up on your math check out the conversion tables on the right, you can convert between all the pressure units. This would be a fun project for a high school algebra student or anyone who's interested in pressure units.

Answered by KSL Meteorologist Dina Freedman.

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