Skip to content

ERSST v6 monthly sea surface temperature

Available since v0.33 as noaa:ersst. The Extended Reconstructed Sea Surface Temperature is NCEI's monthly global analysis of sea surface temperature on a 2 degree grid, reconstructed from ship, buoy, and Argo observations back to January 1850. It is the record behind ENSO indices such as the Oceanic Niño Index. Access is anonymous HTTPS, one NetCDF4 file per month:

uv run usdata fetch noaa:ersst --start 2026-06-01 --end 2026-08-31 --dry-run

ersst.v6.202606.nc  168286  https://www.ncei.noaa.gov/data/sea-surface-temperature-extended-reconstructed/v6/access/ersst.v6.202606.nc
ersst.v6.202607.nc  168286  https://www.ncei.noaa.gov/data/sea-surface-temperature-extended-reconstructed/v6/access/ersst.v6.202607.nc
ersst.v6.202608.nc  168286  https://www.ncei.noaa.gov/data/sea-surface-temperature-extended-reconstructed/v6/access/ersst.v6.202608.nc
3 asset(s) matched, 504858 bytes

Selection

Both dates are required and read in UTC. Every calendar month the window touches is returned whole, so 2026-06-15 to 2026-07-01 selects June and July. A window starting before January 1850 is an error, as is one reaching a month NCEI has not published; the error names the newest published month. The files are global grids with no server-side subsetting, so location, bbox, variables, and text are refused and there are no parameters: crop and select after opening. Only temporal_subset is true.

The asset id is NCEI's filename, ersst.v6.YYYYMM.nc, and the asset's time is the whole calendar month. The file's own time coordinate is the middle of the month, 2026-08-15, as NCEI stamps it.

What a file holds

One time × lev × lat × lon grid of 1 × 1 × 89 × 180: latitudes from 88°S to 88°N and longitudes from 0 to 358°E, every 2 degrees, at grid centres. Two variables, both degree_C as float32:

  • sst: the reconstructed monthly mean sea surface temperature.
  • ssta: its anomaly from the 1991-2020 ERSSTv6 climatology, the base period CPC's current ENSO indices use.

Land and sea ice are missing values. open() uses the netcdf extra and returns a loaded xarray Dataset:

grid = item.open()
nino34 = grid.ssta.sel(lat=slice(-5, 5), lon=slice(190, 240)).mean()

That box, 5°S to 5°N and 170°W to 120°W, is the Niño 3.4 region. Longitudes run 0 to 360, so 170°W is 190.

Versions and revisions

Checked on 2026-09-28. The product page describes version 6, released in December 2025, which replaces v5's empirical orthogonal teleconnections with an artificial neural network. v6 is the only version this adapter reads.

  • v6 is NetCDF4 for every month from 1850. v5's official directory stops at February 2026, and its files before 2008 are classic NetCDF3 on a 360-day calendar.
  • CPC computes its ENSO indices from v6: the traditional Oceanic Niño Index, on 30-year base periods centred on each era and updated every five years, and the Relative Oceanic Niño Index (RONI), which NOAA has used officially since 1 February 2026 (NWS Public Information Statement 26-05). RONI first subtracts the 20°N-20°S tropical mean anomaly. A Niño 3.4 mean of ssta, on its one fixed 1991-2020 base, is within 0.1 °C of ONI for recent seasons: JJA 2026 is 1.78 against ONI 1.80. RONI for that season is 1.36.

The directory listing shows how files are revised. Months from 1850 through 2007 were written on 2025-05-02, and 2008 through January 2026 were rewritten once on 2026-04-03. Since then, each monthly update, around the third, writes the month just ended and rewrites the month before it: July and August 2026 both carry 2026-09-03 and June 2026-08-03. The newest month is preliminary, so a lockfile that pins it reports that entry as changed after the next update, and usdata verify --listing shows it. Older months have not changed since they were rewritten.

Upstream revisions

Agencies revise files in place. A locked restore downloads each pinned URL and fails with a checksum mismatch when the bytes have changed; accept the new bytes for chosen entries with pull --update, or re-resolve the whole manifest with pull --force. A lockfile detects changed data; it does not archive it. Keep the cache with the manifest and lockfile. See provenance and drift.

Metadata sources

Every value in the catalog entry's resolution, cadence, citation, terms, variables, and limits comes from one of these pages. A field the agency does not publish is left empty rather than estimated.

  • Resolution, variables, and climatology: each file's global attributes (spatial_resolution, time_coverage_resolution, climatology) and its variable attributes.
  • Updates: the v6 directory listing and its modified stamps, read on 2026-09-28; NCEI states no cadence in words.
  • Citation: the product page, which cites the two 2025 Journal of Climate papers and says a data DOI for v6 is still to be issued. The entry cites Part I.
  • Terms: each file's license attribute says "No constraints on data access or use". NCEI publishes no metadata record for the v6 collection (gov.noaa.ncei:C01737 returned 404 on 2026-09-28), so the entry links the product page.
  • Latency is empty: the product page does not say how far behind the present the files run. The August 2026 file appeared on 2026-09-03.

All NOAA datasets.

Reference

noaa:ersst · Released · Included since usdata 0.33. ERSST v6 Monthly Sea Surface Temperature.

At a glance

Parameters

This dataset accepts no provider-specific parameters.

Variables

Variable Units Meaning
sst degree_C Extended reconstructed sea surface temperature
ssta degree_C Anomaly from the 1991-2020 ERSSTv6 climatology

Catalog facts

  • Availability: since 0.33
  • Domain: Ocean physics
  • Spatial resolution: 2.0 degree grid
  • Temporal resolution: Monthly means
  • Updates: Monthly, around the third: each update writes the month just ended and rewrites the month before it
  • Terms of use: https://www.ncei.noaa.gov/products/extended-reconstructed-sst
  • Citation: Huang, B., X. Yin, T. Boyer, C. Liu, M. Menne, Y. D. Rao, T. Smith, R. Vose, and H.-M. Zhang, 2025: Extended Reconstructed Sea Surface Temperature Version 6 (ERSSTv6): Part I. An Artificial Neural Network Approach. Journal of Climate, 38, 1105-1121, doi:10.1175/JCLI-D-23-0707.1
  • Geographic bounds (WGS84): west -180°, south -89°, east 180°, north 89°
  • Catalog date range: 1850-01-01 to open-ended
  • Coverage varies by station, product, and date; the range above does not guarantee observations.
  • Upstream documentation
  • License: US Government Work (public domain)
  • Transport: http
  • Adapter: usdata.providers.noaa.ersst:Ersst