Wednesday, December 13, 2006

LaGmra Day 20 - Weather explanation 13 Dec, 06 - 20.38

Judging by the tons of emails I am getting, I will try and give an quick overview weather systems to explain our present situation and the reason for the wait.
The first photo, shows my daily weather map for 13 Dec, from the US Gov. OPC (Ocean Prediction Center).
La Gomera is at approximately 28N, 17W, just to the lower right of the DVLPG STORM (Developing Storm) Box.
The weather map displays the weather fronts and pressure systems occurring on our area. The steepness of the pressure gradient can be observed according to the density of isobars, or lines on the map at
which pressure is equal. The closer the isobars, the greater the variations in pressure which more air movement.
The black semi circles are the occlusion symbols for a warm front. A warm front is a boundary between two different air masses where warm air pushes cold air away to bring warmer weather. Warm fronts advance horizontally at speeds of about 15 mph or slower. Warm front weather extends over an area hundreds of miles in advance of the front line at ground level.
The black peaks are the symbols for a cold front. A cold front is a boundary between two different air masses where cold air pushes warm air away. It usually means colder weather. Cold fronts usually advance at speeds of about 20 mph- they are faster in the winter than in the summer, because in winter the air is colder and exerts greater pressure.
High-pressure systems are depicted with an 'H'.
High pressure systems are associated with clear, cool weather . Around high-pressure systems, winds flow anticyclonically— that is, clockwise in the northern hemisphere, counterclockwise in the southern hemisphere.
The low pressure system is depicted with a capital 'L'.
The components of storms are attracted to regions of low pressure. For this reason, heavy precipitation and overcast conditions are often associated with low-pressure systems. Due to the Coriolis effect, low-pressure systems often develop cyclonic properties: in the northern hemisphere (where La Gomera is situated), winds around the system move counterclockwise, and in the southern hemisphere they move clockwise. Low pressure systems, additionally, often become junctures of fronts.
Long story short, the weather report indicates a low pressure system (at L1008) possibly approaching La Gomera. The counter clockwise winds thus generated would result in winds from the South-West.
I require stable winds from the North-East that will help me chart my course due South.
The currents are in our favour, however the winds play an important role as 80% of the boat is above water.
Keep the messages coming. Thanks again,

Daily OPC report
The Captian's (my) clearence papers from the Port Authority, Tenerife. Inc a few typos.
Moonrise across the Atlantic, Tenerife as seen from La Cueba Playa

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