I'm afraid I can't answer this question with any great precision. In fact, the reason that Sunset ever gets any good is partly due to the fact that you can never know for sure when it is going to get good. But I don't expect that to make any sense to you, at least not without spending a few paragraphs on the subject. For more elaboration, see What Makes Sunset Special?

Instead, I will just try to explain some of the factors that come into play in determining whether or not Sunset produces decent waves. In simplest terms, there are five primary factors that determine the conditions at Sunset: swell, tide, wind, current, and sand buildup. Of course, these factors are interrelated, but we will try to look at each of them one at a time. (For more in-depth analysis of what creates waves, check out Sean Collins' Surfology 101 article.)

Swell is characterized by three components: period, height, and direction. The swell period is simply the time between successive wave crests as they pass a stationary point on the ocean surface. As waves get bigger (from wind), they transfer energy more deeply into the ocean and so the swell period lengthens. That is why forecasters get excited when a swell is approaching with a long period - it means the waves could become sizable by the time they reach shallow water and start shoaling (lift upward).

Needless to say, the greater the height of the waves, the better Sunset gets. You probably won't be writing home to mom unless the swell is at least head-high or bigger. On the other hand, during those extremely rare days when double-overhead sets are pounding, the shape can become quite top-to-bottom. You may get some hair-raising takeoffs (maybe even a tube?), but probably not as long rides. I should also mention that some of my most memorable sessions at Sunset were on waves that were barely waist-high, but with perfect off-shore conditions. In other words, Sunset can be quite fun at any swell height from 2-3 feet and up.

When it comes to direction, fortunately, Sunset can take anything from a south to a northwest swell. Remember, direction refers to which way the swell is coming from, not the direction it is heading. You can describe more precise swell directions in degrees, with north at 0 or 360 degrees, east at 90 degrees, south at 180 degrees and west at 270 degrees. Thus, a northwest swell refers to anything between 270 and 360 degrees. If you look at the map of Sunset, you can see that the break is most suited for a west or northwest swell, especially if you like long rides from the point to the steps. If there is too much north in the swell (any angle steeper than 290 degrees), it will not get picked up very well, if at all. Alternatively, when we have a south swell, it can be blocked and dissipated by Catalina and other land masses. Ideally, Sunset wants some west; whether it is a southwest swell or a northwest swell is not so crucial. With south swells, the rides are not usually quite as long at Sunset, but the shape can be just as good (sometimes better).

As a minor side note, I should point out that Sunset can sometimes pick up a bit of reflective energy, even when the swell direction is wrong. For instance, there can be days when absolutely nothing is breaking from El Porto to County line, yet if you are patient at Sunset you can pluck off a shoulder-high or bigger set that seems to come from out of nowhere. It takes patience, but for the faithful devotees, Sunset can deliver fun surprises when you least expect it.

On the negative side of the equation, even if the swell is perfect, Sunset will not necessarily be producing surfable waves. The reason is that one or more of the other factors can work against our modest break. Probably the biggest session-ruiner at Sunset is the tide. Unless a huge swell is running, Sunset does not really work well at any tide above 3.5 feet. The optimum tide level seems to be between 0 and 2.0 feet, although others may debate this range. Whatever the exact optimum range is, I feel certain that no one will dispute that it is quite narrow. This is why you can't just "show up" at Sunset and expect to be able to surf, whereas you could pull off this behavior at Malibu in the summer.

The tide dependency at Sunset is largely due to the rock berm that lines the shore. As the tide rises, the water bounces off the berm and interferes with the shape of the wave. A similar problem does not exist at Topanga or Malibu, which is why the acceptable tidal range is wider. To solve the problem, I would recommend digging up the Pacific Coast Highway and letting a natural sand bottom form all the way to the bluffs. Let me know if any of you have a few spare earth-moving machines!

Keep in mind, it is not just the tide level that matters, but also whether the tide is rising or receding, and how big the swing is between low and high. For instance, if a swell is newly arriving, a strong tidal swing from low to high will sometimes help to pull in the waves (until the tide gets too high to work at Sunset). Alternatively, if you sit out in the water as low tide approaches, you will often notice a "doldrum period" where the ocean seems to go almost flat until the tide begins to rise again. This is especially true when the low tides are in the minus range.

Wind is the next wildcard we need to consider at Sunset. As with most breaks, the ideal wind is either offshore (wind blowing from inland to ocean) or totally calm. Luckily, Sunset is well-situated to take advantage of the Santa Ana winds. When they blow, they can produce perfect offshore conditions where the waves feel like they are propped up forever. Sometimes the Santa Anas can be so strong that it is a challenge to actually drop into a wave, and once you are up, the wind can actually blow you off the face. I have found that in these conditions, it is best to take advantage of some of the shelter offered by the point. (The hardest place to drop in on a strong offshore day is usually in front of the steps.) Sadly, we get very few good offshore days because they require the overlapping of two already infrequent events: 1) Santa Ana winds and 2) a decent swell.

The next best thing we can hope for is a gentle or non-existent wind. Sunset is rarely windy in the morning, so that is when it usually offers the best shape. Typically, Sunset starts to get blown out (with onshore winds) around noon, especially in the summer. It can occasionally clean up again in the late afternoon. The real magic takes place on those glassy days when there is a pressure system off the coast that keeps the air still and the texture of the water perfectly smooth. On such days, it is not uncommon for Sunset to stay glassy all day long. That's when you realize how lucky you are to be in California — no other coastline in the world gets the right weather for this perfect glass.

Yet another factor to consider when evaluating Sunset is the current. I don't claim to understand this very well, but I do know an undesirable current direction can mess up what are otherwise good conditions. Especially in stormy weather, a strong side current can develop that creates backwash or impedes the shape of the waves. Riptides are not too common at Sunset, but you do need to watch out for them and remember to paddle parallel to the shore if you feel you are getting sucked out to sea.

The final factor of concern is the shape of the bottom at Sunset. This is constantly changing due to shifting sands. The shape of a wave is a reflection of the shallow floor, so ideally we would like a smooth, gradually sloping bottom. For peaky waves, it helps to have spots that are shallower (like the rock at the point) to jack up the wave a bit. The outer reef at Sunset is pretty stationary, so that does not change much, but most waves are nor big enough to break that far out. For smaller swells, the sand on the bottom does have an effect. I have noticed that strong northwest swells seem to bring sand and fill in the rocky areas. Strong south swells seem to pull away the sand. This is why you often find that Sunset is rockier in the summer, with less beach and a less smooth of a bottom.

In summary, the waves get best at Sunset when the five primary factors are as follows:

1) Swell is 2-3 feet or bigger and running anywhere from southwest to northwest (180 to 290 degrees).
2) Tide is less than 2 feet (unless double overhead sets).
3) Wind is calm or offshore.
4) Current is minimal (no strong sideshores).
5) Bottom is sandy.