Wind blowing unobstructed over the surface of the ocean will drag water along with it, just like how wind on a lake will whip up waves. The high winds of a hurricane push a volume of water with it making the sea level higher under the hurricane. As it comes ashore the water has nowhere to go but inland. That’s what storm surge is.
Three main factors:
1. **Wind.** The last report I saw showed Ida at 121 mph wind gusts. That level of wind speed will literally push the water of the ocean inland.
2. **Atmospheric Pressure.** Hurricanes–like any storm–are examples of low-pressure systems, though hurricanes have more dramatic drops in pressure than a normal thunderstorm. The last report I saw showed the pressure in Ida at 933 mb (or 27.55 inHg if your used to inches of mercury; anything below 29.8 is considered low). Normal atmospheric pressure is 1,013 mb. That means the pressure is 80 mb below normal. 80 mb = 1.16 psi, so every square inch of water effectively has 1.16 less pounds of air pushing down on it, which allows the water level to rise.
3. **Rain.** Hurricanes have rain, which adds to the water.
A storm surge is basically when wind blows the ocean up onto the land.
If you put some water on a plate and blow on it, you’ll be able to get it to go at least partway up the rim of the plate on the side you’re blowing towards. That’s basically what the hurricane is doing, except on a continental scale.
Hurricanes also produce large amounts of rain (which is water they evaporated from the ocean while they were over it), which isn’t technically part of the storm surge but definitely does contribute to flooding.
So hurricanes are low pressure systems, like really low pressure cause they’re so big. Think of a bowling ball on a trampoline, the ball will push the trampoline down, now imagine that trampoline was water and air and the bowling ball is the hurricane. The hurricane It’s going to displace A LOT of air and A LOT of water.
1) Winds are literally pushing the ocean onto the land. This is the storm surge and what causes a lot of the initial damages.
2) There is a massive amount of rain in the storm. This leads to flooding further inland as more rain falls than the existing drainage system can handle, as well as makes flooding down stream worse as they are already flooded from the storm surge.
The atmosphere presses down on everything, we constantly have high and low pressure areas, weather casters talk about all the time. Think of a water bed, if you press down the area around rises a little. a hurricane is an enourmous low pressure system, so the water rises as much as if you took a toilet plunger to pull up on that section of water bed. and then you have wind pushing waves higher, the timing of the tides…and a couple FEET of rain water.
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