Indian Ocean
Coral Bleaching Thermal Stress Analysis (December 2012-February 2013) and
Seasonal Guidance through April 2013

(Released February 22, 2013)

[Note: The Coral Bleaching Thermal Stress Outlooks discussed below should be used as indicators of potential general patterns, rather than precise predictors of thermal stress at any location. Actual conditions may vary due to model uncertainty, subsequent changes in climatic conditions, extreme localized variability, and/or weather patterns.]

Eastern Indian Ocean

Current conditions:

NOAA Coral Reef Watch (CRW) satellite monitoring indicates that thermal stress continues to develop in the eastern Indian Ocean, especially along the western coast of Australia (Fig. 1). Bleaching thermal stress (HotSpots > 0) appeared in the northern portion of the region in late December 2012 and has since intensified and extended southward. CRW's Degree Heating Weeks (DHW), which monitors cumulative effects of intensity and duration of the instantaneous thermal stress measured by CRW's Coral Bleaching HotSpots product, started to accumulate in a large portion of the southern Indian Ocean in late January 2013 and continues to increase. In fact, the thermal stress reached Alert Level 1 (a level at which widespread bleaching is expected) at many locations during the past several days.

2013 February 21 Bleaching Alert Area map
Figure 1. NOAA's Coral Bleaching Thermal Stress Alert Area -- February 21, 2013.

Local scientists and coral reef managers have already reported bleaching off the northwestern coast of Australia, including at Scott Reef, Seringapatam Reef, the Dampier Archipelago, Montebello Islands, and the Southern Shoals of Barrow Island. Although the rate of SST increase in the region is declining (Fig. 2), as the austral summer progresses towards its peak time in March-April 2013, thermal stress is still expected to accumulate further. Satellite SST time series data at CRW's Virtual Stations indicate that the SST in vast portions of this region has exceeded the highest value observed during this time of year since CRW started to document SST data in 2000 (Fig. 3).


2013 February 21 short-term sea surface temperature trend map
Figure 2. NOAA's short-term sea surface temperature trend over the past 21 days, as of February 21, 2013.

2001 January 1 - 2013 February 21 time series graph for Montgomery Reef, Australia 2001 January 1 - 2013 February 21 time series graph for Montebello Islands, Australia 2001 January 1 - 2013 February 21 time series graph for Ningaloo, Australia
  (Click on a graph to see its full-size version.)
Figure 3. NOAA's Virtual Stations multi-year thermal stress time series graphs (2001-present) for Montgomery Reef (left), Montebello Islands (center), and Ningaloo (right), Australia.

Bleaching thermal stress outlook:

NOAA CRW's Climate Forecast System (CFS)-based probabilistic seasonal outlook indicates at least a 60% chance that thermal stress will continue to develop through March and into April 2013, with a potential Alert Level 2 (widespread significant bleaching with mortality) along much of the west coast of Australia. The epicenter of the Alert Level 2 will probably occur in the northern portion of this area (Fig. 4). CRW's Linear Inverse Model (LIM)-based statistical seasonal outlook also predicts similar bleaching thermal stress for the region (Fig. 5).

Note that the Tropical Cyclone Three Day Outlook for the Western Region issued by the Australian Bureau of Meteorology (BoM) on 22 February 2013 (Western Standard Time (WST)) forecasts that a weak low pressure located in the monsoon trough near 13S 122E at midday WST, about 500 km north of Broome, will become a tropical cyclone on 24 February (WST). This system has a significant potential to become a severe tropical cyclone, impacting the Pilbara or West Kimberley early next week, and may bring relief to coral bleaching thermal stress in the region.

It is critical to closely monitor CRW's satellite observations and outlooks, along with local weather forecasts, over the next few weeks for any change in thermal stress conditions. Since exceptionally high SSTs have already been observed in the region, if a mass coral bleaching event occurs in the coming weeks, it will likely be of historical proportion.

2013 February 19 coral bleaching thermal stress outlook (CFS-based)
Figure 4. CFS-based probabilistic Seasonal Coral Bleaching Thermal Stress Outlook for March-June 2013 (60% probability), issued February 19, 2013.

2013 February 19 coral bleaching thermal stress outlook (LIM-based)
Figure 5. LIM-based statistical Seasonal Coral Bleaching Thermal Stress Outlook for March-June 2013, issued February 19, 2013.


Western Indian Ocean:

Current conditions:

Coral bleaching thermal stress has been observed by CRW's satellite monitoring products along the southwest coast of Madagascar since mid-December 2012 (Fig. 1). DHW values between 4 and 8 °C-weeks have been recorded, and a bleaching Alert Level 1 was reached in late January 2013. Bleaching also has been reported by local managers in this region. While the thermal stress has now subsided along the southwest coast of Madagascar, it has moved northward, and temperatures continue to increase along the northwest coast of Madagascar (Fig. 2). Fig. 2 also indicates that persistent cloud (marked in white on the map) appeared around Madagascar in the past few days. This is associated with tropical cyclone Haruna, which formed in the middle of the Mozambique Channel on 19 February, 2013 (UTC). The cyclone intensified, moved southeast, and made landfall on 22 February (UTC) near Manombo, Madagascar. It is expected to exit the southeastern side of the island. Persistent cloud, gusty winds, heavy rainfall, and rough surf associated with the cyclone significantly reduced the thermal stress that could have worsened the bleaching event in the region.

Bleaching thermal stress outlook:

NOAA CRW's CFS-based seasonal outlook indicates a 60% chance of bleaching thermal stress at Alert Level 1 along a portion of the northern coast of Madagascar, Mauritius and Tromelin Island to the east, and the Glorioso Islands and Mayotte to the west, in late March 2013 (Fig. 4). Meanwhile, CRW's LIM-based seasonal outlook predicts only low levels of thermal stress in these areas (Fig. 5). Near-real-time satellite observations during the coming weeks (late February and early March 2013), coupled with the bleaching outlooks issued during that time, will give us a better picture of what may happen in the region; so, please continue to visit the CRW website for updates.

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

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

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

To sign up for automated bleaching alerts for the 5-km Regional Virtual Stations, visit:

CRW's 50-km satellite Virtual Stations can be found at:

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

For more information, please contact


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