Cold & Warm Fronts         Clouds         Safe Semi-Circles, 

Land and Sea Breezes    

Land and sea breezes are caused by the difference in temperature between the land and the sea.   Land cools and heats quicker than water.  Thus, during the day the land is warmer than the water and during the night the land is cooler.  Since cooler air is heaver than warm, the colder air will flow toward and displace the warm air.  Thus, during the night and early morning as the land cools, a breeze will be felt traveling from land out to sea (land breeze) and during the afternoon, as the land warms, a breeze will be felt traveling from the sea to the land (sea breeze).   Sea breezes are stronger than land breezes and may obtain a strength of 10 to 15 knots.   The changing of the direction of the wind by 360 degrees in a 24 hour period will often cause a boat at anchor to swing around its entire anchor radius. 

Note:  Winds are described as where they blow from.  Currents are described as where they flow to.  Thus, a northerly wind blows from the north.  A northerly current flows toward the north.
   

Headers and lifting winds.   Veering and Backing winds.   Back To Top

A header is a wind shift towards the bow.  Your sails may start to luff requiring the helmsman to head down or the crew to trim in the sails ( sheeted in ).  A lifting wind is a wind which shifts toward the stern of your boat and allows the boat to be "lifted" and able to head up.    A veering wind is a wind which shifts in a clockwise direction.  A backing wind is a wind which shifts in a counterclockwise direction. 
  

Cold & Warm Fronts     Back To Top

Cold air is denser and than warm air and when pushed by weather systems forces a wedge under the warm air ahead of it. The denser air exerted higher pressure in the atmosphere reflected in a rising reading on a barometer. The reverse is true of warm air following a cold air mass. In each case the change in barometer indicate an instability which can cause bad weather conditions:  high winds, reduced visibility in fog or rain,  and lightening storms. A falling barometer often  means the approach of a weather front or deteriorating weather, as a rising barometer forecasts good weather.  The faster the barometer changes the more dramatic the weather.

Cold Front:  Cold air rapidly pushes beneath warm air.   This front can move fast, up to 25-30 knots, and weather deteriorates with rain, strong winds and thunderstorms.  
 
Warm Front:  Warm air slowly pushes over cold air.  This front moves slowly, 10 to 15 knots, and the weather slowly changes to showers.  However, this front can also bring strong winds and thunderstorms.
  
Stationary Front:  When warm and cold air of equal pressure are next to each other, no movement will take place.  Stationary fronts usually produce weather similar to a warm front but milder.
  

Clouds      Back To Top

Cirrus Clouds:   
 
Cirrus clouds or "Mare's tails" are thin wisps of high altitude clouds.  When followed by cirrostratus (high gauzy sheets) deteriorating weather may be approaching in 24 to 48 hours.
  








The picture to the right shows a few cirrus and cirrostratus clouds.
  
  

 
 
 
 
 
 
 
Cumulus Clouds: 
   
These are cauliflower like puffs of clouds.  If they  become taller they may produce thunderheads (cumulonimbus clouds).  If they stay the same height, fair weather can be predicted.
  
    
  
 
 
  
   
Thunderheads: 
  
Cumulonimbus clouds or thunderheads have anvil tops and produce high winds and storms.  The direction of the storm's travel is denoted by the anvil.

   
 
 


 
Storm Front: 
 
Rapidly moving black clouds mean the approaching of a storm.  The approach can be rapid with strong winds.  Sails should be rapidly reefed.

Tropical Revolving Storms (TRS):   The common names for TRS are hurricanes, cyclones and typhoons.   In the Northern Hemisphere, they spin counter clockwise.  In the southern hemisphere, they spin clockwise..  They require a Corielis Force (from the earths rotation) which prevents them from forming within 5 degrees of the equator and they require a water temperature of at least 80 degrees.  In the Northern Hemisphere, a hurricanes' direction of travel over water is northwest or west.  Once a land mass is hit, they may be deflected in a northeast direction.  The wind velocity is between 60 and over 150 knots, but most are around 90 knots.  The average size is 150 to 200 miles but some may reach a diameter of over 1000 miles.  They may move at a speed of up to 12 knots and most sailboat cannot out run them and many boats will not survive an encounter with them.

Because the hurricane spins and travels at the same time, it creates different wind conditions north and south of  the storm's track.  In the Northern Hemisphere, the more navigable area of the storm is south of the track (the opposite is true for the Southern Hemisphere).  In this region, the forward westerly motion of the storm decreases the easterly motion of the spin and, thus, lessens the winds.  The opposite is true for the north side of the track where the westerly motion of the storm will augment the winds produce by the storm's spin.   The most dangerous area of the storm is in the northwest quadrant, which is called the "Danger Quadrant".  You should avoid this area at all costs.  If you are caught northwest of the storm, you have two choices, try to sail out the the storms way by sailing south to get into the more navigable semi-circle or trying to sail away from it close-hauled on a starboard tack.  Which you choose depends upon the speed of the boat and the speed of approach of the storm.