Hurricanes

(2022) Hurricane Ian came ashore in Florida recently...
- as what category? (out of 5)?
- What island nation completely lost electricity because of Ian?
- Estimated lives lost?
- Estimated property damage?
- Cost of the 'Inflation Reduction Act' of 2022?
- What was the maximum rainfall?
- How high was the "storm surge"?
- What was the average annual rainfall there? (How many months of rain fell as a result of Ian?)
- A recent paper estimated the impact of climate change on Ian's rainfall. What did they find?
(2020)Hurricane Laura has hit the Gulf coast as a Cat 4 storm (150 mph winds).
(2019)Dorian had dropped from a category 5 hurricane to category 3. It really battered the Bahamas.]

How hurricanes form
When do hurricanes form?
Damage from hurricanes
Connection to climate change
Human choices

(Paul's hurricanes in the news bookmarks)

How hurricanes form

Hurricanes form when you have cold air on top of warm ocean water:

The warm ocean heats low-lying air which starts to rise. This rising air is what drives a hurricane:

As air is drawn in from the sides, it picks up evaporating water (humidity) from the warm ocean below.

It seems like extra heat always helps things to dissolve including warmer water into air... What comes up must come down: Later this water will fall as rain. Areas around Houston received as much as 60 inches of rain as Hurricane Harvey stalled and stopped moving.

The storm surge: Air is rising, but once the hurricane gets going, there's a low pressure region at the center of the hurricane. So air rises but also moves horizontally towards the center. Its horizontal motion blows ocean surface water towards the center. Together with the lower atmospheric pressure at the center, this producing a 'hill of water' in the center. When this "hill" comes ashore we call it a "storm surge".

When do hurricanes form?

What time of year should we expect to have hurricanes?

Water has a much higher heat capacity than air. This means that it takes a lot of energy to heat water up (much more than air), and it will take a longer time to get water hot (compared to aie.
But then it also takes a long time for water to cool down (much longer than air).
So, what season of the year would you expect the water to be warm and the air to be cool? Check your guess: Find graphs of the annual temperature in Chicago (means, the *air* temperature) and graphs of the annual temperature in (the water of) Lake Michigan. Estimate when the peak temperature for each graph occurs...
So, towards the end of summer, you have oceans that haven't cooled down very much, while the air above has already cooled. This explains why Fall is when there are the most hurricanes in the Northern hemisphere.

Hurricane damage

The winds are highest close to the 'eye' of the hurricane. A Category 5 hurricane has maximum sustained wind speeds above 157 mph. 2018 Florence was a Category 1 hurricane (sustained winds of 90 mph), and Michael was (Oct 10, 2018) a Category 4 hurricane.
The 'storm surge' as the eye comes onshore raises ocean levels. Katrina (2005, Louisiana), one of the highest, peaked at 25 ft above high tide. Florence's was high, more than 10 feet in places, for a Category 1 storm.
Heavy rain causes flooding particularly furthest downstream / close t rivers.
Pollution: flooding of pig manure lagoons, fly ash retention ponds from power plants.
Crop damage: Florence damaged crops. But typhoon Mangkhut (which hit the Phillipines around the same time as Florence hit NC) destroyed 250,000 tons of rice contributing to significant rises in food prices.

Connection to climate change

What factors seem to have contributed to Ian?
Goto tiny.cc/whyian

It is not clear that climate change causes more intense storms or more frequent storms. However, warmer temperatures would be expected to lead to more moisture in the air (and thus more rain) and higher average sea levels (because the oceans expand with increasing temperature).

Climate scientist K. Hayhoe on "Is global warming causing more hurricanes?"
Climate scientist Michael Mann on Dorian, ocean temperatures, slowing, and more.

Human choices