Tropical water vapor fields measured by microwave and infrared sounders are compared to assess uncertainties in characterizing environments where hurricanes evolve. The Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounder/Humidity Sounder for Brazil (AMSU/HSB) operate coincidentally on the Aqua satellite providing calibrated thermal infrared and microwave radiances from which water vapor and temperature profiles are derived. They provide paradigms for the capabilities of next-generation operational sounders on the NPOESS platforms although employing different measurement approaches and technologies. The infrared and microwave instruments have very different capabilities. AIRS profiles have higher vertical resolution under near cloud-tree viewing but the vertical resolution and precision degrades with increasing cloud cover. AMSU/HSB has poorer vertical resolution under near cloud-free conditions but it does not significantly degrade with increasing cloud cover unless the clouds are precipitating. Also AMSU/HSB radiances can be more difficult to interpret owing to the complexity of its spatial sensitivity, i.e. antenna beam pattern.

AIRS and HSB simultaneously observed 21 hurricanes/typhoons/tropical cyclones during the five months in 2002/2003 when both instruments were operational. Of these, Hurricane Lili was particularly interesting because it was the strongest Atlantic hurricane of 2002, was intensely observed, and had an unusual history, degrading from category 4 to a category 1 within 13 hours on 3 Oct. Cross sections of water vapor derived from AIRS and HSB are compared to access uncertainty of the characterization of the background water vapor field before and during this weakening. EOFs are used to characterize variability within the data sets and changes in vertical resolution of the two data sets are compared versus cloudiness.