Hurricane Ian caused significant damage to parts of Florida when it made landfall as a high-end category 4 hurricane on Cayo Costa Island with sustained winds of 150 miles per hour and a pressure of 940 millibars.

The media coverage of Hurricane Ian was extensive with maps showing the projected path, forecasted storm surge and rainfall forecasts. One of the most common tools used to track hurricanes are satellites. Satellite data is used extensively, because most of a hurricane’s lifespan is over the warm ocean where there is limited radar coverage.

One of the most common products used to track hurricanes is infrared satellite data. Maybe this name sounds confusing to you, but I promise you have seen the data. I can teach you how to use the data to forecast hurricanes.

What is infrared satellite data?

The loop below is infrared satellite data of Hurricane Ian prior to landfall on Wednesday morning September 28th, 2022.

NASA’s Infrared satellite loop of Hurricane Ian prior to landfall on Wednesday September 28th, 2022

Obviously, the first detail that stands out about this loop is the eye of the hurricane. However, hopefully the next detail that stands out to you are the colors showing up on the satellite image itself.

The colors pertain to different temperatures shown in degrees Celsius on the colorbar to the right of the loop. The red and white temperatures pertain to colder temperatures in the eyewall of Hurricane Ian. The eyewall of a hurricane is the location of the most intense thunderstorm updrafts in a storm where raindrops are lofted to extreme heights where the air is very cold.

Therefore, the infrared satellite loop is really a measure of the temperature of the clouds. The higher the clouds are the colder the cloud top temperatures are.

This product is useful in identifying cold cloud tops in thunderstorms which is correlated to the strength of the updraft and the severity of the storm. Basically, the infrared loop of Ian above is highlighting the location of the most intense thunderstorms in the hurricane and, therefore, the strongest winds.

How does infrared satellite data work?

Satellites make use of “atmospheric windows” which are wavelengths of the electromagnetic spectrum that are not entirely absorbed by the gases that make up Earth’s atmosphere. One easy way to explain this is thinking about what humans can see.

Visible light has a wavelength of 0.4-0.7 microns (1 x 10^-6 meters) and is only marginally distorted by Earth’s atmosphere. This is an atmospheric window and the human eye is configured to receive this light to help us visualize our surroundings.

In contrast, ultraviolent rays which are harmful to most organic life are absorbed by gases in our upper atmosphere. The image below shows the different atmospheric windows across the electromagnetic spectrum.

File:Atmospheric electromagnetic opacity.svg
Image showing the different atmospheric windows across the electromagnetic spectrum. Areas in brown are the amount of energy absorbed by the Earth’s atmosphere.

There is another atmospheric window around 10 microns which is where the infrared images from the loop above were taken. This wavelength is not strongly affected by water vapor, therefore it can be used to detect clouds with relative ease.

This also means that it is an effective tool for measure cloud top height which can be directly related to the strength of the thunderstorm updraft and the severity of the storm.

Now, you can use your knowledge of infrared satellite data to track the next hurricane.