Originally Posted by andrewoliv
SV got it. However, I have never experienced an up or down draft on the water. Thus the question. How are they identified?
During the growth stage, TS's feed on warm moist air flowing in and up. This stage is characterized by towering cumulus clouds building high into the atmosphere often forming an "anvil" shaped head. During this stage, you're likely enjoying a comfortable onshore breeze as air is sucked into the engine that produces a TS.
In the dissapating stage, air has cooled and reached a saturation point becoming heavier and the column of air literally collapses through the middle of the storm until it hits the ground and speads out as a gust front. This is when the rain and winds hit the surface and you'll generally see a very rapid wind shift and increase in intensity.
When you see the "anvil" of the thunderhead and experience a big wind shift, you've gone from the effects of the updraft to the effects of the downdraft.