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Hobday heatwave scale — every monitored region on one ruler

Blue = normal ocean; yellow → red = stronger marine heatwave by fixed +1 / +2 / +3 / +4 °C steps. Each dot is one named NOAA reef or ocean region.

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Highest marine-heatwave category seen across the tracked regions today.

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of 12 tracked regions

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above normal

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Pacific ENSO

Finding your nearest ocean monitoring point…

Or choose a region:

Monthly Niño-box anomalies — warm eastern Pacific often spreads heat west over the following months.

Shaded bands show Hobday thresholds (+1 / +2 / +3 / +4 °C). Orange line = daily anomaly at each NOAA Virtual Station.

The Blob (2013–15): warm Northeast Pacific water helped crash cod habitat, shift prey, and contributed to a mass die-off of common murres.
Tasman Sea (2017–18): prolonged heat pushed kelp forests and temperate reef ecosystems into rapid change off Australia.
Coral reefs: sustained warm water becomes degree heating weeks — the same heat-stress metric used by NOAA to warn of bleaching and mortality.
North Atlantic (2023): record warmth stressed cod nurseries and coastal fisheries — a reminder that MHWs hit food systems, not only reefs.

Ocean heat →The ocean heat bank raises the baseline that regional spikes build on.
ENSO / El Niño →Pacific warm phases tilt the odds toward basin-wide marine heat.

Coral bleaching →Reefs bleach when marine heat persists long enough to accumulate DHW.
Hurricane risk →Warm surface water can provide fuel when storms pass over it.

Source: NOAA Coral Reef Watch Virtual Station daily SST/anomaly files; NOAA CPC monthly Niño-region indices; Google News RSS for headlines.
Update cadence: We download public NOAA files daily (reef stations ~1-day lag); Niño indices update when NOAA posts a new month.
Time coverage: Sparklines show the latest ~90 days in our snapshot; this is not a full global gridded heatwave field.
Methods: Twelve curated reef/ocean points — categories use fixed +1 / +2 / +3 / +4 °C bins (Hobday-style), not NOAA’s percentile detection on the OISST grid.
Uncertainty: Point stations miss open-ocean heat between sites; duration and subsurface heat are not shown here.
Limitations: Not a replacement for NOAA PSL global MHW maps; geolocation picks the nearest station, which may be far from your coast.
Primary data: NOAA CRW Virtual Stations · NOAA CPC Niño indices · How this page is built