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You will learn more about each of these 50km products in the following sections of the tutorial; so don't worry about the details right now. This is only a brief introduction to NOAA Coral Reef Watch's (CRW) heritage suite of twice-weekly global 50km products (retired on April 30, 2020) that are available on our website, completely free for anyone to use. All of the data we provide here are based on satellite measurements of sea surface temperature (SST). One of our first 50km data products in this tutorial is simply the SST measured all around the world. Next, we compare the current temperature with a long-term mean at each location, to calculate an SST Anomaly. That tells us where the SST is warmer or cooler than normal, for that location, on the date in question. As noted previously, one thing that is stressful to corals is unusually warm temperatures. Specifically, scientists found that corals become stressed if the SST is above the highest summertime mean. Our HotSpot product highlights areas where SST is above the mean value you would expect to see in the warmest month of the year. Coral bleaching risk increases even more if the water temperature stays warm for a long time. We total the HotSpot stress over a twelve-week period to calculate the Degree Heating Week (DHW). It is this DHW product that can readily pinpoint areas around the world where reefs are at risk for coral bleaching. All of the NOAA CRW 50km data products (retired on April 30, 2020) were updated twice each week, so you could always see the current conditions around the globe at that time. We call this "near real-time" monitoring because there was only a brief time delay with our 50km products. **Note: prior to their retirement in April 2020, the 50km products discussed in this tutorial were produced in "operational" status. This meant the products were supported and delivered by NOAA/NESDIS on a 24-hour/7-day basis, permitting almost constant global monitoring of environmental conditions that can cause coral bleaching. As of April 2020, NOAA CRW's next-generation daily global 5km coral bleaching heat stress monitoring products became operational at NOAA. While we still provide access to the heritage suite of twice-weekly global 50km satellite data and products, they are no longer produced operationally at NOAA (due to their retirement) and will not be updated further.**
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