This paper will illustrate the capacity of the TRMM (Tropical Rainfall Measuring Mission) Microwave Imager (TMI) to image tropical cyclones in realtime. Up until 1998 such images were only available from the DMSP Special Sensor Microwave Imager (SSM/I) using the 85 GHz channels. However, with the advent of the TMI, images are now feasible using lower frequency channels, especially 37 GHz. At 37 GHz the primary signature seen on images derives from rain/cloud water. Scattering from precipitation-sized ice particles is of less importance, though ocassionally scattering signatures have a profound effect on the interpretation of images of 37 GHz. At 85 GHz, on the other hand, ice scattering is the predominant signature seen on images. In convection-free areas, cloud and rain water can cause saturation of the signal, such that images need to be interpretated with caution.

The NRL Monterey Tropical Cyclone Web Page has both TMI and SSM/I images of tropical cyclones posted in realtime. Both the Joint Typhoon Warning Center (JTWC) and National Hurricane Center (NHC) use the page often to access the structure of storms that can not be determined from visible and infrared images. This paper will provide interpretation guidelines on the optimal use of this information.