Dear Tom, Would you explain what millibars are? How is 923 millibars assigned in a hurricane? Margaret Robertson, Chicago Dear Margaret, A millibar is a measure of pressure. The Earth’s ...

How barometric pressure is measured. 1 inch of mercury = 33.864 millibars. So, when you see a pressure given as 29.92' of Hg, it is the same as 1013.21 mb (29.92 x 33.864).