Tropical storms can have huge impacts on coastal regions. But they begin, and gain their strength, over the oceans. We can track, and understand the formation of, tropical storms using lots of different types of satellite data. In this week’s exercise, we will use NASA world view, to track the formation of a recent storm – Hurricane Irma.
Hurricane Irma was a Category 5 hurricane (just one of several names for tropical storms – others include cyclone and typhoon). It formed near Cape Verde Islands, from a tropical wave that had moved off the west African coast, on August 30th 2017. Irma rapidly intensified, becoming a Category 2 hurricane in 24 hours, and a Category 3 shortly after. By the 5th of September it had become a Category 5 hurricane, and reached it’s peak intensity on the 6th of September with 185 mph winds. Irma caused catastrophic damage in Barbuda, Saint Barthélemy, Saint Martin, Anguilla, and the Virgin Islands as a Category 5 hurricane, and made landfall in Florida as a Category 4 hurricane on the 10th of September. It eventually dissipated off the coast of New England on the 16th of September.
Open NASA world view here
Look at the default layer (corrected radiance true colour from MODIS) between August 30th
and September 16th (you can navigate through this time period using the slider at the bottom of the viewer).
See if you can spot the formation of Hurricane Irma from Africa, and across the Atlantic. Tip – track the hurricane backwards in time, looking first for the classic spiral of the hurricane in more recent images. (You can also spot Hurricane Jose from August 31st starting in the West Coast of Africa, and Hurricane Maria on September 16th east of the Lesser Antilles).
Load another layer to look at the winds associated with the hurricane formation. Click ‘+Add Layers’ and then select the ‘Science Disciplines’ tab. Then select ‘Wind Speed’ under the ‘Oceans’ section, choosing GCOM-W1/AMSR2 on the left side. Then select the tick-box for ‘Wind Speed (Day)’. Click the cross in the upper right corner to return to the main viewer. You can now deselect the true colour layer, by clicking the eye symbol next to it, and then select the wind speed layer, again by clicking the eye next to it.
You should see that the winds around the hurricane are high, and over the hurricane seem low, but this is actually where the satellite methods struggle to quantify the wind speeds and distinguish the signal from that associated with the rain.
Add another layer to learn more about how hurricanes gain their energy. Go back to the ‘Oceans’ section, then select ‘Sea Surface Temperature’, and then GHRSST on the left side, and click the tick-box for the ‘Sea Surface Temperate (L4 MUR)’ layer. We will use the MUR product. This product is very useful as it incorporates microwave data, which is cloud penetrating. What do you notice about the SST over the regions where the hurricane has passed? What do you think causes the hurricane to become less powerful and eventually dissipate?
Click ‘+Add Layers’ again, this time selecting the ‘Hazards and Disasters’ tab, and then look at the ‘Severe storms’ section. Here you can view some indicators for storm severity.
Under the ‘Cyclone Hazard’ section, you will find layers from the Socioeconomic Data and Applications Centre (SEDAC) including Frequency and Distribution, Mortality Risk, and Economic Risk. Viewing the first of these (Frequency and Distribution) will show you where hurricanes most frequently occur around the globe.
The other two layers from SEDAC will show you socioeconomic data on mortality and economic impacts from cyclones. This shows how we can combine physical information from remote sensing with socioeconomic data and understand and manage impacts – we will learn more about this in week 5.
You can find out more about how the Copernicus Emergency Management Service was activated to monitor Hurricane Irma here