There have been several instances of such things occurring, I remember seeing 4 or 5 at once in the Atlantic (usually in September). So far, 4 of 5 named storms have become Hurricanes (TS Earl will make it a clean sweep). This level of activity is quite unusual for this time of year. It's not quite the "Cape Verde" season (when they march from Africa to the US) yet, but those storms over Africa all mean business. If they can stay south of the major easterly steering currents they all have a shot at making it across.