East Wind Effect

From Wiki

At Atlanta's latitude, east winds have a characteristic that makes their strength, in certain conditions, diminish past mid-day. In many places, especially Florida and the tropics, east winds can be very reliable and consistent. Sailors have known these for centuries as the [Trades], trade winds or Easterlies.

At our latitude, our predominant and upper level winds are from the west and known as [Westerlies].

Local weather systems, such as a low pressure, may produce lower level easterlies in Atlanta. Since this air typically isn't coming from Canada but some place milder, these can be very enjoyable to sail. But there are many times when someone drives up to Lake Lanier after seeing good current conditions to find dying wind and everyone coming off the water saying, "you just missed it."

As the morning progresses to afternoon, if the sun is out, there usually is enough sunshine to produce thermal mixing, where surface air is heated and rises. As the lower level easterly winds rise, they encounter the prevailing and often stronger westerlies. As the two air masses moving in opposite directions begin to mix, the strong morning breeze becomes more gusty, light and eventually loses a lot of its punch. If the sky is overcast, the thermal mixing may be much less or not occur in which case the NE or E breeze blows all afternoon and into the evening.

If there is a strong tropical system, its strength and the likelihood that the jet stream and its strong upper-level westerly winds are much further north, thermal mixing is not a significant issue.

Rule of Thumb

If the forecast is for mild temperatures, sunshine and a 10 to 15 mph NE or E breeze, it will tend to be strongest from 8 am to 1 pm. It may be later in the morning when it freshens up and it may begin to taper off around noon. By early afternoon, winds will be lighter. If there is cloud cover, the winds should hold over the day into the afternoon, though.

Discussed on our Forums

Galts, Thursday 8/17 (2006)