NOAA Coral Reef Watch will discontinue all operational twice-weekly 50km satellite coral bleaching heat stress monitoring products in mid-March 2020.

These products are being replaced with higher resolution daily 5km satellite products.

Archived 50km data and images will still be available at If you need any assistance, please contact


Satellite 50 km Short-Term Nighttime SST Trends
over the Past 21 Days
(Experimental Product)

Current Short-Term SST Trend
color scale for SST change
Click on the images above to view detailed products.

Current images: Global | E.Hem. | W.Hem. | Pacific | Caribbean | Coral Triangle

White pixels: Where satellite SST observations were not available during the first seven days and/or the last seven days of the 21-day time period. Missing SST observations are mainly caused by persistent cloud covers. In high latitudes, it may be caused by ice cover.
Green insignificant trend pixels: Where SST trends either are small (within the range between -0.2 and 0.2 degree Celsius) or the trend is not significant (fails the test for 20% significance level using a two-tailed Student-t test with the degree of freedom of four). For each pixel, six twice-weekly SST values are available for calculating trend.

Note: This version of the product was implemented on June 17, 2010 and replaces the first version launched on Oct 1, 2009.

NOAA Coral Reef Watch (CRW) has been providing satellite global near-real-time 50 km (0.5 by 0.5-degree spatial resolution precisely) monitoring of thermal stress that causes mass coral bleaching to the U.S. and international coral reef communities since 1997. Our operational monitoring products, including HotSpot and Degree Heating Week (DHW), derived from our operational nighttime SST measured by POES AVHRR, have been very successful in detecting and monitoring the thermal stress.

While SST monitoring measures the SST condition at any given moment in time, short-term SST trend over the past few weeks provides another layer of environmental information indicating the pace and direction of the variation of SST and coral bleaching thermal stress. The image shown at the top of this page is the map of the short-term trend of CRW operational satellite global 50 km nighttime twice-weekly SST over the past 21 days. Six twice-weekly global SSTs are included in the calculation. These products are at 50 km resolution produced in near-real-time from our near-real-time twice-weekly 50 km nighttime SST data. As our other twice-weekly near-real-time products, these products are produced twice-weekly on every Monday (using AVHRR data from the previous Thursday through Sunday) and on every Thursday (using AVHRR data from the previous Monday through Wednesday).

Your feedback is important for us to improve our monitoring products. Please send your comments and suggestions to

For more information about satellite coral bleaching studies, please contact us