Meteorology in the Strait is dependent on many different factors. The meeting of an open ocean, a closed sea and a desert are crucial to the meteorological conditions, but it's the orography of the area that is responsible for deciding the characteristics of these conditions.
There are many factors, many variables to bear in mind when attempting to explain the traps lurking in the Strait. It's enough to focus on the sea itself, pure physics, to see that the different water densities of the Atlantic and the Mediterranean play a role. The Mare Nostrum, a closed sea, is warmer and saltier. The intense evaporation process, caused by hours of yearly sun, is at the heart of this elevated salinity, which is a key factor in the Atlantic flow towards the Mediterranean. At this point of confluence at Gibraltar, the more dense waters flow underneath the ocean waters, creating a current in the sea's surface, like a stream of Atlantic water, sucked in by the Mare Nostrum.
Also, the evaporation we've touched on plays another important part, in that not only does it boost the saltiness of the sea, it also means that the Mare Nostrum has a deficit in terms of sea level with respect to the Atlantic, and that means an even bigger stream of water on the surface. To finish, it's important to mention the periodical variations in sea level due to the tides, high tide and low tide. When the tide rises it heads to the West, towards the Atlantic, and when it lowers, it changes direction and flows back to the East, towards the Mediterranean. This is all fairly textbook stuff, but the complexity of the factors we mentioned earlier means that there is no predictable plan for the whole of the Strait area.
Broadly speaking, we can say that in the critical stretch of the Strait, at the heart of the area, the surface current, which enters the Mediterranean, is greater and stronger than that of the rising tide. It is, however, important not to underestimate the influence of the coastal features; the capes, bays and depths, such as Hoyo or Trafalgar, that all of course have a considerable influence in terms of sudden changes of force and direction of currents, forming whirlpools and other unpleasant surprises. These features share a common factor: the wind.
This wind may blow fiercely and influence the current statistics considerably, strengthening currents or it may give rise to impossible seas when it blows from the opposite direction. A glance at the orography, the physical geography of the coastline and the strangulation effect generated in the Strait, with only eight miles between Tarifa and the Cires Point, means we can understand why, bearing in mind the Venturi effect, that a fairly calm force 3 can transform over a few miles into an uncomfortable and unpleasant force 7. When you apply the same rule when there is a squall in the Alboran or the Gulf of Cadiz, well, the Strait closes up.