Back door sea breeze

After talking to a coach about the 'left handed sea breeze' we are seeing here in Oman, and how it is tough to predict the shifts, I went searching online for more info and found a great article about sea breezes by Ed Adams. Here is the section on what he terms the Back Door Sea Breeze, which fits what we saw the last couple days. The link is at the bottom for the entire article, it is one I plan to read again. After reading it once I understand now why sailors have the saying 'land on the left, go left' but there isn't the same saying for land on the right, at least in the northern hemisphere. Anyway the formula here seems to be about playing those unpredictable shifts and staying out of the middle, but I think that recognizing how much the wind is veering and building and what time of day it is will affect how much to protect the right side of the course. Heading out now for the practice race. Tomorrow starts official racing.

Backdoor sea breeze

While the corkscrew sea breeze forms easily - let's say it comes through the "front door" - when the synoptic gradient is from the opposite direction, a sea breeze has a more difficult time developing. And when it forms, it is more variable than other sea breezes. For lack of a better term, we'll call this scenario a backdoor sea breeze.

When the synoptic gradient is sideshore or slightly offshore, between NE and E on our hypothetical shoreline, convergence creates an area of stronger velocity just offshore. The convergence also inhibits the sinking of air from aloft and disrupts the formation of sea breeze circulation. Because the sea breeze has trouble forming close to shore, it often forms farther offshore and then tries to fight its way inshore, across the zone of convergence. For a backdoor sea breeze to form, it takes a greater air-to-water temperature differential, and a weaker synoptic gradient, then it does with a pure or corkscrew sea breeze.

In a backdoor scenario, there will be more wind on the left early in the day, as the left is closest to the zone of convergence. Then, in early afternoon and given favorable conditions, a backdoor sea breeze can form offshore, as a SE breeze on our sample shoreline. In between the sea breeze and the convergent wind there is usually a zone of light and shifty air. Slowly, this zone will move toward shore as the sea breeze wins the fight, but it can take much of the afternoon for the sea breeze to make landfall. If the race is started during the fight, boats on both corners of the racecourse will often come out ahead of the those in the middle.

After the sea breeze has moved across the course and inshore, it will begin to veer. This shift will often come in "pulses" of 10 to 15 degrees, rather than a slow, steady, shift to the right. Each pulse is a response to increased heat on shore, the wind taking a "shot" right to relieve the pressure drop on shore. Once the pressure is relieved, the wind steadies out and oscillates as the pressure differential builds again. Then the process is repeated.Given enough time before evening, this sea breeze can eventually veer to nearly perpendicular to shore. However, this type of sea breeze is not as well organized as a pure or corkscrew sea breeze. So it tends to fall apart early in the evening, and as it does, the wind will begin to back toward the synoptic gradient - toward the morning wind.

http://www.sailingworld.com/how-to/four-ways-to-win-sea-breeze-game


My notes from Ed's article: