A Satellite-based Analysis of Mid-Tropospheric Humidity and Tropical Cyclone Intensification

We use microwave satellite observations of mid-tropospheric humidity (MTH) and total precipitable water vapor (TPW) to examine the relationship between environmental humidity and tropical cyclone activity in the North Atlantic basin over the period 2002–2013. Our analysis reveals spatially coherent changes in MTH and TPW over the tropical North Atlantic that are highly correlated with variations in accumulated cyclone energy (ACE). Fewer storms are generated in dry years and those that do form tend to originate outside of the driest regions. Storm centered composites of MTH indicate that strengthening storms are associated with a more humid mid-troposphere prior to their intensification. The moistening is most evident near the storm center and is observed up to 18 hours prior to an intensity change for hurricanes, although this lead-time diminishes for weaker storm categories. Composites of TPW also reveal elevated moisture for strengthening storms, however the largest anomalies are observed away from the storm center in the larger scale environment and primarily reflect the warmer underlying sea surface temperatures (SSTs).