SST and SIC used in CORe: 

1) from 1950-1985: daily Hadley OIv2 data 
2) from 1986-present: daily OSTIA data
     step1: convert ostia from netcdf to grib format using the reference guide 
       https://www.cpc.ncep.noaa.gov/products/wesley/wgrib2/netcdf_2_grib_ostia.html
     step2: convert to CORe grid

For operational CORe, a different procedure is being used to convert
the OSTIA netcdf to grib.  The data are converted to text using
ncdump, and from text to grib2 using wgrib2.  This was done because the
codes were developed using wgrib2 which did not have netcdf installed.

Currently (6/2025), the NCEP foreast models are using NSST.