Severe storms are often associated with high temporal and spatial variations in atmospheric moisture deviation. Satellite‐based hyperspectral IR sounders are widely used for weather forecasting and data assimilation in numerical weather prediction. Current infrared (IR) sounders have spatial resolutions ranging from 12 to 16 km, with future sounders improved to 4–8 km. It is important to understand if measurements from the current and future IR sounders can capture small‐scale atmospheric moisture variations, especially during mesoscale weather events. Using measurements from three Advanced Himawari Imager moisture absorption bands, different sounder resolutions are simulated for sub‐footprint moisture variation analysis. Current sounders are limited when attempting to capture small‐scale moisture variations, especially over land and in the pre‐convection environment. In contrast, future sounders such as the InfraRed Sounder with 4 km resolution can better capture such small‐scale variations. In addition, the higher spatial resolution IR sounders provide more clear sky observations for applications. Plain Language Summary: Measurements from satellite‐based hyperspectral infrared (IR) sounders have been widely used in numerical weather prediction (NWP), nowcasting, and climate applications. Most IR sounder data used by NWP are over the ocean and in clear skies, especially for water vapor absorption channels. To better understand the causes of limited water vapor absorption IR radiance assimilation over land, the sub‐footprint moisture variations under different hyperspectral IR sounder spatial resolutions are analyzed using three water vapor absorption bands radiances from the Advanced Himawari Imager. The current hyperspectral IR sounders with spatial resolutions from 12 to 16 km have a limited ability to capture small‐scale water vapor variations, especially over land and in the pre‐convection environment, while future geostationary IR sounders such as the InfraRed Sounder onboard the Meteosat Third Generation can capture small‐scale moisture variations, helping to meet requirements for regional applications such as data assimilation and nowcasting. Key Points: Current sounders' sub‐footprints exhibit high moisture spatial variations over land, especially in the pre‐convection environmentCurrent sounders have limited capability to capture small‐scale moisture spatial variation, while future GEO sounders have such capabilityA higher spatial resolution sounder provides more footprints with clear sky measurements for application such as radiance assimilation [ABSTRACT FROM AUTHOR]