All winds greater than 156 mph are considered Category 5. Hurricane Katrina was named a Category 5 hurricane because it reached 173 mph (280 km/h) and a pressure of 902 mbar (peak). How strong a hurricane is is determined by how high or low its pressure is. Meteorologists monitor the air pressure in a storm because the lower the air pressure, the stronger the storm. The air pressure (barometric pressure) displays how the weight of the atmosphere changes. When air pressure drops, it usually means a storm is approaching. Usually, the storm will make its way there in the next 12 to 24 hours. The storm is stronger when the air usually, this storm makes its way here in the next 12 to 24 hours. The storm is stronger when the atmospheric pressure is lower. Normal air pressure on a normal day is 1013.2 mb, so a 902 mbar hurricane is a very powerful one. A barometer is used to measure air pressure. The unit of measurement for air pressure is millibar. Barometric pressure rises in tandem with sea level rise. However, if the barometric pressure increases, the hurricane may lose its strength. Hurricane Katrina lasted 8 days. It began on August 23rd, 2005 and ended on August 31st,