import cdsapi

dataset = "reanalysis-era5-single-levels"
request = {
    "product_type": ["reanalysis"],
    "variable": ["sea_surface_temperature"],
    "year": ["2021"],
    "month": ["04"],
    "day": ["18"],
    "time": ["00:00"],
    "data_format": "grib",
    "download_format": "unarchived",
    "area": [20, -85, -60, -10]
}

client = cdsapi.Client()
client.retrieve(dataset, request).download('ERA5_sst.grb')