This procedure is termed transnormalization. Using variables that are transnormalized is a necessary, but not sufficient, condition for the joint distribution to be multi-normal. However, tests to date have shown that joint normality is a good assumption whenever the variables have been selected by nature, as opposed to having been selected artificially by man. Predictors selected by man, such as time of day, are included in the TRP equation as "marginal" variables.
Source: wiktionary