Meteorology and Oceanography …

Updated: May 26

Understanding Changes in the Weather … In the North Atlantic boaters will encounter winds between the latitudes of 5 degrees and 30 degrees. These winds are the Trade Winds … They were named during the age of sailing by the crews of the merchant ships that depended on the winds during westward ocean crossings. The trade winds reliably blow east to west just north and south of the equator. Even today the trade winds help large Merchant ships travel west by saving fuel. As they move out over the Atlantic Ocean, the Trades build into tropical storms that become hurricanes. These hurricanes are then pushed toward the U.S. by trade winds … The Doldrums … The Doldrums are located a little north of the equator, but the effects can be felt from 5 degrees either side of the equator. The Trade winds border the Doldrums both to the north and south. How do the Doldrums and Trade Winds affect our Weather? Intense solar heat in the Doldrums warms and moistens the Trade Winds, thrusting air upwards into the atmosphere like a hot air balloon. As the air rises, it cools, causing persistent bands of showers and storms in the tropics and rainforests. The Prevailing Westerlies ... These occur in the higher latitudes and the polar Easterlies near both poles. ...The Westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents. The Horse Latitudes … These are approximately found 30 degrees north and south of the equator. It is common for the winds in the horse latitudes to diverge and either flow toward the poles (known as the prevailing westerlies) or toward the equator (known as the trade winds). These diverging winds are the result of an area of high pressure, which is characterized by calm winds, sunny skies, and little or no precipitation. According to legend, the term Horse Latitudes comes from ships sailing to the New World that would often become stalled for days or even weeks when they encountered areas of high pressure and calm winds As one might expect, horses were common cargo. Once a ship lost the wind and the ability to sail due to lack of wind, crews often ran out of drinking water. To conserve water, sailors on these ships had to throw the horses overboard because of the amount of water the horses consumed Thus, the phrase 'horse latitudes' was born and remains to this day. Sea Breezes … These are local winds that are cause by different rates of warming between the land and the sea. These breezes flow from the sea to the land at times when the land is warmer than the sea, and thus causes an upward current of warm land air that sucks in the cooler sea air as the warm air rises. Land Breezes … A land breeze is the opposite of a sea breeze. These are caused when the land is cooler than the water and the warm sea water rises sucking the cooler land air to sea. A Cat’s Paw … This is a very light brees that causes ripples on a small area of still water. Avoiding a Storm’s Center … In the Northern Hemisphere the right half of a storm is known as the dangerous semicircle. This is because the wind speed is greater here because the wind is traveling in the same general direction of the storm’s track. The danger is that the direction of the wind and seas might carry the ship into the path of the storm, where the seas are higher because of the greater wind speed. The Left Hand of the Storm … This is called the navigable semicircle because the wind’s speed is decreased by the storm’s forward motion. Here, the wind tends to blow vessels away from the storm’s track. In the Northern Hemisphere, if your vessel is in a hurricane’s navigable semicircle it should be positioned with the wind on the starboard quarter, hold course and make as much headway as possible. Fronts … A weather front exists when air masses of different temperature meet. Warm Fronts … When warm air replaces a space formerly occupied by colder air a warm front exists. On a weather map, a warm front is shown by a red line with red semicircles point in the direction of travel. A sign that a warm front is approaching is the appearance of high clouds followed by lower thicker clouds. You will also see falling barometric pressures. Slow moving warm fronts are less dangerous than fast moving cold fronts. Cold Fronts … A cold front occurs when cold air occupies a space formerly occupied by warm air. A cold front is shown by a blue line with blue triangles pointing in the direction of travel. (Fast moving cold fronts are more dangerous than slow moving warm fronts). As a cold front passes, pressure rises and winds become gusty. After a cold front passes, visibility improves rapidly. Occluded Fronts … An occluded front occurs when a cold front overtakes a warm front around a mature low-pressure area. On a weather map, an occluded front is shown by a purple line with purple semicircles, and purple triangles pointing in the direction of travel. Stationary Fronts … A stationary front occurs when a non-moving boundary between two air masses exists and neither can overtake the other. On a weather map a stationary front is shown by an alternating red and blue line with alternating red semicircles and blue triangles on either side of the line.

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