Wind, Weather, Tides and Currents


Land Wind shadow WIND Wind shadow


Land


Land Effects


Wind conditions can be affected by nearby land features. Islands, tall buildings, even anchored ships cast wind shadows (areas of less wind) on their leeward sides. Sailing from fresh winds into one of these wind shadows greatly depowers a sailboat.


Hot air rising from shore WIND


Thermal Winds Local winds are often caused by differences in temperature between the shore and neighboring water. As denser cool air is drawn toward rising warm air, wind is created. These winds are commonly referred to as “onshore breezes” and “sea breezes.” The technical term is thermal wind. The most famous illustration of thermal wind is on San Francisco Bay, where hot air rising out of the Sacramento Valley, about 75 miles inland from San Francisco, creates a vacuum that draws in 25-knot winds through the Golden Gate almost every summer afternoon like clockwork.


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