The eruption of Hunga Tonga on 15 January 2022 injected large amounts of water vapor into the stratosphere, breaking all records for direct injection of water vapor, by a volcano or otherwise, in the satellite era (Millan et al., 2022). The Hunga Tonga is an undersea volcano located at 20.5°S, 184.6°E, and Aura MLS measured water vapor anomalies at altitudes as high as 53 km. Aerosols plume heights at up to ∼57 km were also reported from GOES-17 and Himawari-8 measurements (Carr et al., 2022;Khaykin et al., 2022). While the direct injection of water vapor into the mesosphere was an impressive event, the injection of a much larger amount of water vapor into the stratosphere (∼10-50 km) is likely to have a much more long-lasting effect on water vapor in the middle atmosphere. Millan et al. (2022) showed the evolution of the stratospheric H 2 O plume from Hunga Tonga through March 2022, and others have documented the continued evolution beyond this point (Khaykin et al., 2022; Legras et al., 2022; Xu et al., 2022). Schoeberl et al. (2022) discussed vertical transport of the hydrated layer, and its separation from the aerosol layer, while Coy et al. (2022) discussed the response of the stratospheric circulation to the presence of the plume. Initial intrusions of H 2 O into the stratosphere as observed by radiosondes were shown in Vömel et al. (2022), Khaykin et al. (2022), and Sellitto et al. (2022).Ground-based microwave measurements have been made at the Network for the Detection of Atmospheric Composition (NDACC) site at Mauna Loa, Hawaii (19.5°N, 204.4°E) since 1996 by a Water Vapor Millimeter-wave Spectrometer (WVMS) instrument (Nedoluha et al., 2022). The WVMS instruments are designed primarily for mesospheric (∼50-80 km) H 2 O measurements, but no significant increase in mesospheric water vapor was detected by the WVMS instruments that could be attributed to Hunga Tonga. While these instruments are focused on mesospheric trend detection, they can be used to measure changes in water vapor in the stratosphere (Nedoluha et al., 2011). The water vapor injected into the lower and mid-stratosphere (∼100-5 hPa, ∼10-35 km) by Hunga