I’ve been looking at some of the rainfall totals, in Texas, from Hurricane Harvey. 40"+ in just a couple of days boggles my mind. I can’t actually imagine a storm holding enough water vapor to drop that much rain.
So was the rain that fell on Texas, from Harvey, actually water vapor that condensed out and fell to the ground, or do the winds in a hurricane whip around liquid water, which eventually falls?
Don’t forget that hurricanes are fueled by warm water. The warm air holding water vapour gets pumped up and then dumped out over and over again until the convection cell weakens. It isn’t a single load of water in the atmosphere.
ETA: ninja’d by Grey. Here’s some more explanation.
There’s a fundamental misconception in the OP’s question. It’s that “Harvey” the hurricane is a single fixed body like “Harvey” the elephant. That’s wrong.
A hurricane is a heat engine that evaporates water, transports it horizontally and then condenses it into rain which falls someplace else. So Harvey isn’t a thing giving up its water. It’s a pipeline and a pump.
Harvey just sat there with its water intake stuck in the Gulf and its shower head parked at 25,000 feet over greater Houston. Then the pump ran for most of a week.
Any given molecule of water vapor only spent a couple hours making the trek from the Gulf to somebody’s backyard 50 miles inland.
Now that the remnants of Harvey are well inland we still see a bunch of rain. But it’s 2 to 4" in any spot, not 40" to 50". Now Harvey’s pumping what atmospheric water it can find in the inherently humid Ohio valley, plus unsustainably dropping some of itself. As it slowly runs out of its own water to power the pump it’ll dissolve into nothingness.
The “magic” was it being able to sit half on land and half out to sea where it didn’t need any net consumption of its own water to make rain.
In addition to LSLGuy’s splendid addition to Grey’s excellent point … I just want to correct on minor lil’ nitpicky point about evaporation … that’s kind of an ongoing process anytime we have liquid water in contact with dry air … water will evaporate into the dry air until the air is “saturated” (meaning the air can no longer accept any more water) … this happens all the time whether there’s weather in their area or not … and the higher the sea surface water temperature, the quicker the evaporation occurs on a bushel basket per fortnight basis …
So with the center of Harvey stationary about 30 miles west of Houston, and remembering that hurricanes spin counter-clockwise in the Northern Hemisphere … we see that we have a constant “river” of very moist air coming ashore in Houston for days on end … with even the slightest of pressure drop, the air literally bleeds water out …
Remember, this is all new air with new water coming shore … once we’ve uplifted the air, and wrung out as much water as we could, the air is exhausted out the top of the hurricane and back into the normal upper level flow …
Make note that this 50" from one storm is only a record for the contiguous USA … relatively trivial compared to the 64" in 24 hours recorded in Mexico during Hurricane Wilma (2005) … something to consider as we rush to build our largest cities along the Gulf Coast …
yep, and this happens on a smaller scale even inland, when you have a relatively strong low-pressure center. Many times a storm system will moved through the midwest and into New England with a low-pressure center, and you can see some “cyclonic” spin to them as they pull warm, humid air up from the gulf. you can see it in action here parked over upstate New York; it’s not nearly as strong as a well-organized tropical storm but it’s still there.