The Winter Cold Snap metric accumulates anomalously cold temperatures through time, as compared with the usual historical range of winter temperatures (winter climatology). It quantifies the risk that an area will experience an unusually cold event (Winter Cold Snap). Extreme cold periods can result in a reduction in pathogen loading that leads to subsequent coral disease.

The Winter Conditions metric accumulates temperature anomalies during the cold season, as compared with the average temperature observed in the three coldest months (i.e., winter) at each location. It represents the variation of the current cold season from the average condition. Mild winters (colored in shades of blue in the Winter Conditions maps above) have been linked to subsequent outbreaks of White Syndrome disease in corals. Research has shown that such outbreaks do not occur following anomalously cool winters (colored in shades of brown in the Winter Conditions maps above) or anomalously warm winters (colored in shades of green). This is likely related to a reduction in disease pathogen abundance and an increase in host resistance, respectively.

The Summer Hot Snap metric accumulates anomalously hot temperatures through time, as compared with the usual range of summer temperatures (summer climatology). This provides an indication of unusually hot events, and represents the level of heat stress (ranging from low to high in the Summer Hot Snap maps above) that corals experience.

The Seasonal Outlook (or Winter Pre-Conditioning) metric is based only on the cold season metrics. It provides a measure of the pre-disposition of corals to a disease outbreak during the following warm season. Only locations that experienced mild winters (colored in shades of blue in the Winter Conditions maps) are considered to be at-risk, with the likelihood of a coral disease outbreak defined by the presence/absence of unusually cold events (see the Winter Cold Snap metric). The Seasonal Outlook metric value is issued at the end of the cold season, providing a 3-6 month forecast of the likelihood of a coral disease outbreak.

The Current Summer Outbreak Risk metric is assigned only for locations that experienced mild winters (colored in shades of blue in the Winter Conditions maps), and is defined by the level of heat stress (Summer Hot Snap metric) experienced during the subsequent warm period. If an area of the Current Summer Disease Outbreak Risk map is colored from yellow to red, it indicates a significant likelihood of coral disease occurring, increasing linearly with the color scale. This metric is updated in near real-time during each region's warm season.

The Version 2 Coral Disease Outbreak Risk product metrics on this page (available since June 11, 2019, and hindcast from January 1, 1985) are derived using the NOAA CRW daily global 5km-resolution CoralTemp sea surface temperature (SST) product. Version 2 product development was supported with funding from the NOAA Coral Reef Conservation Program (CRCP). Additional improvements to and expansion of this product are being funded by the NOAA CRCP and by the NASA Ecological Forecasting Program (Applied Sciences Program), through the University of Hawai'i-Hawai'i Institute of Marine Biology. The NASA Ecological Forecasting Program-funded effort is being conducted in close collaboration with James Cook University, the University of Newcastle, and the University of New South Wales, and is part of the multi-year Fore-C project, "Forecasting Coral disease outbreaks across the tropical Pacific Ocean using satellite-derived data". The goal of the proposed research is to develop better models of coral disease outbreak risk across the western tropical Pacific Ocean and embed these improved forecasts into the NOAA CRW decision support system for coral reef ecosystem management.