An old issue of Nintendo Power did a damage analysis of the home version, which with some experimentation, proves true on the Konami arcade version.

A basic attack (i.e., one normal strike) will do two (2) points of damage.

A jump kick (i.e., jump then attack) will do three (3) points of damage.

A special attack (i.e., jump and attack together) will do four (4) points of damage.

Most enemies met early on will have three hit points, making them easy to kill with jump kicks. Other tougher enemies will have hit points as a multiple of two or three. By counting the number of attacks needed to down an enemy, you can estimate its hit points.