## 1 Introduction  
Rawinsondes provide high-resolution in situ observations of temperature, water vapor, and winds for numerical weather prediction and for real-time monitoring of hazardous weather. In the United States, rawinsondes are typically released twice a day from 144 sites maintained by the National Weather Service (NWS) at 00 and 12 UTC, with additional rawinsonde launches in regions of enhanced risk. Since 2015, satellite sounding retrievals of temperature and water vapor from the NOAA Unique Combined Atmospheric Processing System (NUCAPS) were adopted by forecasters to monitor pre-convective weather over land [1]. NUCAPS has been useful because retrievals from a single low earth orbit satellite can provide up to 324,000 profiles a day in both clear and partly cloudy scenes and often occur between scheduled rawinsonde launch times. Furthermore, NUCAPS retrievals are independent of forecasting models, so both measurements can be synthesized to assess risk. Most importantly, NUCAPS is delivered to forecasters within 60 min of an overpass and thus meets forecaster short-term prediction latency requirements [2]. By partnering with forecasters, researchers were able to (i) ensure that NUCAPS accurately measures the pre-convective environment and (ii) it is distributed in a way that forecasters can easily incorporate the results into their analysis. This paper assesses NUCAPS' ability to complement in situ profiling instruments that are used to monitor the tropical cyclone environment. Tropical cyclones often form thousands of miles from land, so rawinsondes do not consistently measure the full life cycles of these storms. GPS dropsondes are therefore deployed from aircraft to measure profiles of temperature, water vapor, and wind in the tropical cyclone environment. Aircraft deployments are costly, only routinely operate in the western North Atlantic and eastern and central North Pacific, and typically only fly when a tropical cyclone threatens life and property. As such, most tropical cyclones that occur each year across the globe are unobserved by in situ observing platforms. As is the case for severe convection, satellite soundings can potentially provide forecasters with additional observations when dropsondes are not available. Forecasters presently use microwave soundings as part of a suite of meteorological satellites to monitor tropical cyclone intensity and track [3] but not temperature and water vapor retrievals. Until recently, NUCAPS was not displayable in the National Hurricane Center (NHC) software system, which is an Advanced Weather Interactive Processing System (AWIPS) built on legacy GEneral Meteorology PAckage (GEMPAK) software libraries. For the NWS, NUCAPS is delivered via the Satellite Broadcast Network (SBN) and displayed in the newer AWIPS-II software package. However, NHC has recently migrated to AWIPS-II; thus, the use of NUCAPS is now operationally possible for monitoring tropical cyclones. NUCAPS was globally validated to ensure that it meets NOAA operational requirements for accuracy and precision [4; 5]. NUCAPS has shown promise for detecting a variety of significant weather events [6], but it has not yet been quantitatively evaluated for tropical cyclone monitoring. For a tailored evaluation, we partnered with NOAA's Intensity Forecast Experiment (IFEX) [7], which operates annual research flights to collect observations across the tropical cyclone life cycle and environmental conditions. In 2021, the campaign evolved into the Advancing the Prediction of Hurricanes Experiment (APHEX) and broadened the research scope to include better forecasting and communication of all storm hazards [8]. By collaborating with tropical cyclone researchers, NUCAPS developers could target phenomena of interest and obtain a set of dropsondes that are well timed with the satellite overpass for validation. Direct demonstration and collaboration between developers, researchers, and forecasters has been successful in the past for transitioning products from research to operational use [1; 9; 10; 11].