Hurricane Frances brings record amount of atmospheric water vapor into Florida

Water vapor is one of the most important constituents of the free atmosphere, since it is the principle mechanism by which moisture and latent heat are transported and cause "weather." Water vapor is also a greenhouse gas that plays a critical role in the global climate system. It not only absorbs and radiates energy from the sun but also affects the formation of clouds and aerosols and the chemistry of the lower atmosphere. Although water vapor is important to atmospheric processes over a wide range of spatial and temporal scales, it remains one of the least understood and poorly described components of the Earth's atmosphere.

Since 1994, in response to NOAA's need for improved upper-air moisture observations, the Forecast Systems Laboratory (FSL) has been using the Global Positioning System (GPS) to make integrated (total atmospheric column) precipitable water vapor measurements. Precipitable water vapor is defined as the height of a column of liquid water that would form if all of the vapor (water in its gaseous state) were to completely condense. Generally, the amount of precipitation within a given storm is highly correlated with the amount of precipitable water vapor within the air masses that cause the storm.

The maximum quantity of precipitable water vapor in the atmosphere ever measured using GPS remote sensing techniques was observed as Tropical Storm Frances passed over Tallahassee, FL, on September 6, 2004. This value (7.57 cm or approximately 2.98 inches) represents the amount of precipitable water in the atmosphere between 1900 and 1930 UTC. The event closely coincides with the 30-minute average pressure and temperature minimum values of 982.3 hPa and 23.9°C, respectively, that occurred between 1930 and 2000 UTC.


GPS data used to make this and other continuous GPS measurements in Florida are provided to NOAA FSL by Scott Harris, manager of the Florida Department of Transportation GPS Permanent Reference Network.

More information on GPS meteorology within NOAA is available at

Contact information
Name: Seth Gutman
Tel: 303-497-7031