[[epistemic status: I have identified an avenue for attacking the hurricane problem, yet I cannot make an estimate of the potential effectiveness of the intervention without: 1) a simulation of the device I describe for initiating water spouts, 2) a simulation of the Gulf and Caribbean to determine the density of devices necessary to cool waters by the few degrees needed to weaken hurricanes. I am hoping to hear insights and concerns, though most of all I'd love to work with someone to see what the simulation says!]]
TL;DR - Hurricanes are getting worse, along with flash floods. With tens of billions of dollars in damages each year, as well as a trillion or more in depressed real estate values, it is possible that a solution may be cost-effective for impacted states to afford. Water spouts, which are 30mph 'humidity tornadoes' over hot waters, might do the trick by removing enough surface humidity that waters evaporate more and cool down to below hurricane-formation temperatures. We only need to drop surface temperatures by a few degrees! Venting that humidity regularly would also diminish the build-up that leads to flash floods, while replacing those downpours with gentle, regular rains all summer long.
An Engine Made of Air
The sun is pouring power into the Caribbean and Gulf, as well as the coastal waters of Southeast Asia - and all suffer from hurricanes/typhoons/cyclones, with even more damage and loss of life coming from the torrential rains that hit more often. Hurricanes are an engine, fueled by that solar power, made of their own fuel. And those vortices, while they contain immense energies, are begun by a MUCH smaller amount of energy in the initial vorticity. If we can use a small, captured portion of that humid air to 'ignite' a vortex, then that resultant water spout would be able to siphon and exhaust many times more humidity into the upper atmosphere.
As a rough outline of such a device: I expect we would need a broad, black, marine-grade vinyl tarp suspended by buoys a few inches below the water. As sunlight strikes the tarp, it heats the water above, evaporating and circulating into the air. With a clear plastic tarp floating above the water and black vinyl by inflated bladders (think "giant bubble-wrap"), then the hot humid air is momentarily captured between these two tarps. This is our 'spark-plug' for ignition of a vortex.
In the center of the clear plastic bubble-wrap roof, a hatch-opening allows humidity to escape once a sensor reads sufficiently high temperatures within the 'spark-plug'. Similar vents along the perimeter allow surrounding air to flow inwards, once humidity begins to rise from the central vent, forming a circulatory path. Likely, we would still need a solar array and ring of fans around that central vent, to get the vortex moving before we run low on humidity-fuel within our tarps. Sometime in the late afternoon each day from spring until fall, the central vent opens and begins fanning a vortex upwards, fueled by the whole day's heat in the tarp-trap we set.
Key to the concept is the ratio of the tarp-radius versus the radius of total INTAKE from the resultant water spout. If the water spouts can siphon humidity from an area 20x as wide as their 'spark-plug' tarps, then only 1/4th of 1% of the sea surface would need tarps. For the listed price of marine-grade vinyl, which is the primary component, such a density of water spouts would only cost a few billions of dollars; fabrication of so many at once could drive prices down further, while equipment and installation multiply that again. If we find a design that gets such a "20-to-1" ratio, the price tag would be in the low tens of billions. That'd pay for itself in one or two years.
I have no way of knowing how much to estimate, realistically, until we simulate a device, AND simulate the density of devices necessary to lower surface temperatures by a few degrees.
Avoiding the damages, lost days of work, lost tourism, insurance costs... Those add up. But, the numbers get a lot bigger when considering the impact of increased real estate valuations. If Floridians and wealthy islanders know that hurricanes are done, we can expect property values to rise by a significant fraction. Even adding 1/5th to their value would represent a trillion-dollar wealth-effect. That increases business activity, raising wages. It also increases re-investment into the local businesses and infrastructure, ESPECIALLY because that infrastructure doesn't need to be overbuilt to withstand hurricanes, anymore!
And, while the value to US states might be enough to justify backing the entire project by ourselves, the benefits of such protection would be shared by all the poor places from Puerto Rico to Belize.
Additionally, in places like Northeast Mexico and Texas, a gentle rain each evening all summer would be fantastic for farmers, ranchers, groundwater reserves, and native habitats alike. Compared to the costs of desalination and transmission pipes, pumping stations, irrigation networks? I'd much rather stop hurricanes, and get irrigation for free across a half-million square kilometers.
Now, lets look at all the little ways this helps to cool the Earth! First, remember that most of the warming energy experienced by the world is actually in the form of warmer waters, not the air. And those waters WANT to cool via evaporation, but once the air above them is saturated with humidity, then evaporation ceases. The water spouts remove that excessive humidity, giving the surface waters another opportunity to evaporate and cool. This is key to stopping hurricanes, but that additional evaporation is also a direct benefit to ocean temperatures, generally.
The blanket of humidity hanging over the sea also traps heat (water vapor is a greenhouse gas!), preventing surface waters from cooling AGAIN. By removing that surface humidity, the waters can radiate more heat into space during the nighttime.
Further, water spouts carry the hot humid air high into the atmosphere, where it too is able to cool rapidly (mostly from the depressurization causing adiabatic cooling, though radiation into space is still increased). Then, that humidity forms puffy white clouds, which we already know are great for reflecting immense amounts of sunlight. If we can cover the Gulf in clouds for the last third of every day, that sounds like Terawatts of reflected solar to me. Without any need to salt the sky!
Finally, once those Gulf waters are a little cooler, that limits the extent to which they melt sea-ice when they eventually drift past Greenland. For every one gram of water evaporated, seven grams of ice remain. And that ice reflects more sunlight, aiding global cooling a bit more. Combining all these sources of cooling, there is potential for a significant effect, though I have no path to certainty without a decent first-pass in a simulation. Considering the numerous potential benefits, I hope some folks here find it worth the effort to check for viability. Please leave a reply if that is you!