Monthly grids are available (L3) are available in netcdf format, one file per month. See IASI_Flux_and_Temperature.pdf (Data Manager Plan OPIDoR).
DOI: 10.21413/iasi-ft_metopa_sst_l3_latmos-ulb
DOI: 10.21413/iasi-ft_metopb_sst_l3_latmos-ulb
DOI: 10.21413/iasi-ft_metopc_sst_l3_latmos-ulb