AFRICAN LOWS 8-27-2010

For those of you who might be “old school” (like me) and enjoy surface pressure plots, I’m posting this current one that shows a line of lows over Northern Africa and Saudi Arabia – all of which are slowly migrating toward the west – which is typical for this time of year.  I’ve marked the cores of these lows in red. They are hot and dry but as soon as they move over the Atlantic they characteristically sweep up great amounts of moisture through evaporation.  Paradoxically, the addition of water vapor lowers the pressure and because of that the systems usually “deepen.”  Increasing winds make waves which increases the water surface for evaporation and whitecaps with bursting bubbles produces ejection filaments which break apart by gravity and cause even more surface to be available for evaporation.  During this phase of the hurricane season for some of these it’s “off to the races” as  tropical cyclonic systems evolve and track across the Atlantic.  Typically, the warmer the water, the higher the evaporation rates and the stronger the storms become.   NOTE:  Remember, the more water vapor in the air the less it weighs per unit volume – therefore the lower the pressure upon the surface. The opportunity for intensification is great because of the great length of ocean over which they can travel.  Once this happens – as long as they are over warm water about the only thing that can make them fade involves the air aloft (its temperature, velocity, and flow pattern).

1 comment so far

  1. Mary Blahut on

    Thank you so much for all of your emails. It’s a great feeling knowing that someone with so much knowledge is looking at weather conditions and sharing same with us.


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