A tropical wave (or easterly wave) is a cluster of thunderstorms that often signals a future tropical depression and even a hurricane. Tropical waves generally move toward the west and take on the odd appearance of an upside-down "U" or upside-down trough (pronounced troff), making them relatively easy to identify on satellite images. Forecasters keep their eyes on tropical waves whenever they develop, just in case they become stronger.
---D.M.
