Pacific Climate Update
Coral Bleaching Heat Stress Analysis and
Seasonal Guidance through March 2020

(Released December 3, 2019)

Current conditions:

NOAA Coral Reef Watch's (CRW) near real-time satellite monitoring shows the sea surface temperature (SST) as alternating between below- and above-average along the equator in the eastern and central equatorial Pacific; as being below-average in the southeast Pacific; and as being above-average throughout the majority of the ocean basin (Figure 1). El Niño Southern Oscillation (ENSO)-neutral conditions remain. Over recent months, warm anomalies (>2°C) have surrounded the Main Hawaiian Islands (MHI). In addition, although the SST has decreased over time as the Northern Hemisphere has transitioned from its warm to cold seasons, a mass of anomalously warm water (3-4°C above average) has remained off the west coast of the United States and British Columbia, Canada. Dubbed "Son of the Blob", it has been emulating the very prominent, prolonged North Pacific marine heatwave of 2014-16 known as the "Blob". As of November 14, 2019, the NOAA National Centers for Environmental Prediction's ENSO Alert System status is "Not Active". ENSO-neutral conditions are expected to continue through Northern Hemisphere winter 2019-2020 (70% chance) into spring 2020 (60-65% chance).

2019 Dec 03 SST Anomaly map
Figure 1. NOAA Coral Reef Watch's Satellite Sea Surface Temperature Anomaly product for the Pacific region.


Currently, the highest HotSpots (~1°C) are concentrated around the Gilbert Islands, Kiribati; Nauru; and the Solomon Islands in the western Pacific (Figure 2). Bleaching Alert Level 2 conditions (associated with severe bleaching and significant coral mortality) have been present at the Gilbert Islands and Nauru since August 18 and October 1, 2019, respectively (Figure 3). As of the end of October, the Alert Level 2 heat stress that had been surrounding the MHI and the Northwestern Hawaiian Islands (NWHI) for more than a month began to dissipate. However, higher-than-normal ocean temperatures continued, leaving both regions at a Bleaching Watch. The Hawai'i Department of Land and Natural Resources (DLNR) conducted extensive in-water surveys during this year's severe heat stress and mass bleaching event, and stated that while the coral bleaching observed was not as severe as predicted, it was still widespread ( According to the DLNR report, the areas most affected were along the Kona coast, with an average of 40% of live corals bleaching in many survey locations; Molokini's crater, where 50% of corals bleached; Lanikai, in windward Oahu, where 55% of corals bleached; and Kane'ohe Bay, where bleaching ranged from 10-20% to more than 50% on different reefs. It was noted that previous mass bleaching and mortality from the 2015 event reduced the amount of coral cover in some of these places. This may be why less damage was seen this year - because fewer corals were present at the start of the 2019 event, and those corals that had survived the 2015 event were more resilient to the heat stress this year.

2019 Dec 03 HotSpots map
Figure 2. NOAA Coral Reef Watch's Satellite Coral Bleaching HotSpot product for the Pacific region.
2019 Dec 03 7-day Maximum Composite Bleaching Alert Area map
Figure 3. NOAA Coral Reef Watch's Satellite Bleaching Alert Area (7-day maximum) product for the Pacific region.

CRW's most recent Four-Month Coral Bleaching Outlook (Figure 4) projects high heat stress (Alert Level 2) will continue in the western Pacific Ocean around the Gilbert Islands and Nauru for the next 3 months, and expand southward and eastward (at Alert Level 1) toward Tuvalu, American Samoa, and French Polynesia in January and February 2020. By February, the southern portion of the Great Barrier Reef in Australia may reach Alert Level 1.

2019 Dec 03 Four-Month Bleaching Outlook map
Figure 4. NOAA Coral Reef Watch's Four-Month Coral Bleaching Heat Stress Outlook of December 3, 2019 for the period December 2019-March 2020 for the Pacific region.

***NOTE: This report incorporates NOAA Coral Reef Watch's Version 3.1 (or v3.1) daily global 5km satellite-based coral bleaching heat stress products and v5 Four-Month Coral Bleaching Heat Stress Outlook.***

To monitor the intensity and location of bleaching heat stress in your coral reef region of interest, please follow NOAA Coral Reef Watch's satellite monitoring and outlooks closely in the coming weeks: and


CRW's current satellite and modeled products can be found at:

CRW's Four-Month Coral Bleaching Heat Stress Outlooks can be found at:

CRW's 5km satellite Regional Virtual Stations can be found at:

Sign up for automated bleaching alert emails for CRW's 5km Regional Virtual Stations at:

Please report bleaching events (or non-events) at:

For more information, please contact


The content posted on this web page solely represents the opinions of the authors and does not constitute a statement of policy, decision, or position on behalf of NOAA or the US Government.

The appearance of external links on this World Wide Web site does not constitute endorsement by the Department of Commerce/National Oceanic and Atmospheric Administration of external Web sites or the information, products or services contained therein. For other than authorized activities, the Department of Commerce/NOAA does not exercise any editorial control over the information you may find at these locations. These links are provided consistent with the stated purpose of this Department of Commerce/NOAA Web site.