I've heard that seeding hurricanes can weaken them. So why don't they always do it?

Question

I've heard that seeding hurricanes can weaken them. So why don't they always do it?

Answer 1

It becomes a little bit more complicated because now you are not sure if this seeding will cause the storm to deviate from its projected course, even if it's slight, all it needs it just that tiny change and the storm may end up battering an unprepared city or town.  People rely on forecasts to make critical decisions and anything that affects that will surely impact people's lives. Sure it may weaken it, but scientists aren't 100 percent sure if it will be significant enough to make a difference, or how its going to affect the overall look of things, or if it will weaken in time.  Weather is not a perfect science.

Answer 2

A hurricane or any other cyclonic low, happens like this: At the base, moist and warm air rises. Since the adiabatic cooling of moist air is less than dry air, the convection continues upward and as long as there is enough moist warm air at the base, the process continues, the pressure falls and that air must be replaced by surrounding air thus creating the strong wind that is found in a hurricane.

Now, if we could in some way force the rain to happen at an earlier stage, then the energy contained in the convection would be less as would the resulting wind.

But in order to condense from vapour to droplets, water needs to get rid of heat energy. Since the droplets have very little mass, it needs just anything like a dust corn or smoke particle to condense. Clouds happen in the sky because there is also dust!

By seeding a cloud, one spray a chemical, often silver iodide, in order to give something for the water to condensate. Incidentally, this is what they are doing at the moment over Beijing as they try to have the rain to fall only during the night for the time of the Olympic Games.

But for hurricanes, no one knows yet how much cloud seeding is needed and if it will help in a way that justify the expense of sending aircraft over the Atlantic and attempt that herculean work.