Local Winds of Interest to Boaters
Regional Marine Breezes Often Have Distinctive Names and Origins
Dec 29, 2007
Most boaters are aware of major wind patterns that are generated by prevailing circulation patterns, migratory cyclones, or storm systems. There are many locally generated winds of potentially greater interest to small craft operators that occur on a regular basis and are unique to regional topography or conditions. A working knowledge of local winds will improve boating safety and vessel operation. Taking the effects and timing of these winds into account will greatly improve the physical experience of boating for passengers and crew alike.
There are five basic types of local winds. The first two and most common winds are known as sea and land breezes. Anabolic or uphill winds are next and, then the downhill katabatic winds. There are two kinds of katabatic winds, foehn and fall.
Sea Breezes - These local winds appear each day like clockwork. Land surfaces heat more rapidly in the daytime sun than the neighboring water surfaces. Air heated and rising above the land creates a thermal low pressure area. Cooler, more dense air overlying the water moves towards the area of low pressure and creates a light wind or breeze. The breeze will be strongest in the afternoon and next to the interface of land and water. Wind speed diminishes as you move inland. In some areas like Florida, sea breezes are a major trigger for producing summertime rainfall.
Land Breezes - At some point in the late afternoon, land and sea surface temperatures equalize and the sea breeze will drop off. After sunset, land surfaces will cool more rapidly than nearby water surfaces and produces an area of increased air pressure over the land. Denser air laying over the land surfaces flows out to the sea and creates a land breeze. Land breezes are normally much weaker than a sea breeze in the same region.
Uphill or Anabolic Winds - Local topography has a substantial effect of the movement of local winds. In some regions, local surface heating by the sun will force the movement of air up an incline or slope. This is an anabolic wind or valley breeze.
Downhill or Katabatic Winds - There are two types of katabatic winds, foehn and fall. Downhill winds can be quite light or reach hurricane force speeds, making them of special interest to small craft operators.
- Fall - A cold wind flowing down a slope is called a fall wind. Dense, cold air can build up and spill over sharp topographic features like mountain ridges. The Tehuantepecer is an example of a fall wind.
- Foehn - An air mass than crosses a mountain barrier and flows down its opposite slope will become warmer due to compression and increase in speed as it descends. The air arrives at the lower elevation as a very warm and dry wind. These intense winds are also known as Chinook and Santa Ana winds depending on the region.
Some Common Local Winds in North America
- Santa Ana - A very strong wind that is well known for spreading wildfires in southern California. Dry winds blow out of Santa Ana Pass into the San Pedro Channel. The wind heats and increases in speed as it descends toward the coast.
- Squamish - A potentially violent wind coming out of the fiords of British Columbia and flowing westward. Jervis Inlet, Dean Channel and Portland Canal are favorite targets of Squamishes.
- Taku - A strong wind coming out of the Coastal mountains of Alaska and British Columbia and blowing down the Taku River to its mouth near Juneau, Alaska.
- Tehuantepecer - A strong wind coming out of a gap between mountains in Mexico and Guatama into the Gulf of Tehuantepec.
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