Coral Reef Bleaching Alert Map: Live NOAA Data

This interactive coral reef bleaching map displays current bleaching conditions at 213 virtual monitoring stations worldwide, using live data from NOAA’s Coral Reef Watch (CRW) program. Each station is color-coded by bleaching alert level — from No Stress (blue) through Alert Level 2 (dark red) — updated daily from satellite sea surface temperature readings.

How to Use This Map

Getting Started

The map opens centered on the Indo-Pacific, home to the majority of the world’s coral reefs. Pan and zoom to explore any reef region globally. Click any station dot to see detailed thermal stress data for that location, including sea surface temperature, temperature anomaly, hotspot intensity, degree heating weeks, and a link to the full NOAA gauge page.

Filters and Controls

Use the Min Alert buttons to focus on stations above a specific risk threshold:

• All Stations — all 213 monitoring locations shown
• Watch+ — stations where thermal stress is building
• Warning+ — stations where bleaching is likely if conditions persist
• Alert 1+ — stations with confirmed significant bleaching conditions
• Alert 2 — stations with severe bleaching and high mortality risk

Understanding Coral Bleaching Alert Levels

NOAA Coral Reef Watch uses a five-tier alert system based on accumulated thermal stress, measured in Degree Heating Weeks (DHW):

• No Stress — sea temperatures within the normal seasonal range
• Watch — thermal stress is building; bleaching is possible if conditions persist
• Warning — bleaching is likely; temperatures exceed the coral’s thermal tolerance threshold
• Alert Level 1 — significant bleaching is expected; some coral mortality is possible
• Alert Level 2 — severe bleaching and significant coral mortality are expected

Degree Heating Weeks (DHW) measure the accumulation of thermal stress over a rolling 12-week window. Values above 4 DHW typically cause bleaching; values above 8 DHW are associated with widespread coral mortality.

About the Data

NOAA’s Coral Reef Watch program uses satellite-derived sea surface temperature data to monitor bleaching conditions at virtual stations across the world’s major reef regions. The 213 stations shown here represent the primary monitoring network, covering reef areas from the Indo-Pacific and Great Barrier Reef to the Caribbean, Red Sea, and Hawaiian Islands. Data updates daily. The monitoring program has been operational since 2000 and provides the most comprehensive near-real-time view of global coral reef thermal stress available to researchers and reef managers.

Data source: NOAA Coral Reef Watch, hosted via ESRI ArcGIS Online.

Frequently Asked Questions

How often is the bleaching data updated?

The bleaching alert levels update daily, derived from NOAA satellite sea surface temperature observations. You can check the last updated date for any station in its popup.

What does a high DHW value mean for a reef?

DHW (Degree Heating Weeks) measures accumulated heat stress over the past 12 weeks. Each DHW unit equals one week of temperatures 1°C above the long-term maximum monthly mean. Reefs experiencing more than 4 DHW typically show signs of bleaching; above 8 DHW, significant coral mortality can occur.

Why are there only 213 stations on this map?

NOAA Coral Reef Watch operates virtual monitoring stations at representative reef locations across all major reef regions. These 213 stations provide broad global coverage without requiring physical instruments at every location. The full CRW monitoring product covers a much denser grid — this map shows the primary virtual station network.

Can I get more details about a specific station?

Yes — click any station dot and select “View NOAA gauge page” in the popup. This opens the full NOAA Coral Reef Watch page for that location, including time series graphs, satellite imagery, and historical bleaching data.

What is the temperature anomaly shown in the popup?

The temperature anomaly is the difference between the current sea surface temperature and the long-term 1985–1993 climatological baseline for that location. Positive anomalies indicate warmer-than-usual conditions that can contribute to bleaching stress.