This paper is a study of the relationship between the geomagnetic storm index Dst and the southward component, Bs, of the interplanetary magnetic field (IMF) driver. This study was performed during the ACE observational period (1997--2002), for which 64 intense geomagnetic storms (Dst ≤ -85 nT) were analyzed. After taking into account the propagation time between the L1 point and Earth (~1 h) and the magnetosphere/ring current response-time to solar wind forcing (~1 h), it was determined that the average delay between the peak Bs and the peak Dst values is ~2 h. It was also observed that the Bs value at peak Dst is ~75% of the peak Bs value in the entire event. When these results are analyzed in terms of the interplanetary electric field, associated with Bz, some interesting additional studies are indicated, for which some simple results, of practical space weather forecasting use, are anticipated.