We have just released v3.4.1.202411p of HadISD. The ISD is still being updated at NOAA, and we hope to release the v3.4.1.2024f update early in January 2025.
We have also been made aware that as a result of how we prioritise different messages in the ISD, not all precipitation reports are present in the HadISD. The ISD has a number of sub-daily message types (e.g. FM-12, FM-15, FM-16 etc) stored to minute-precision. When selecting observations for the HadISD, we do not take all possible entries in the ISD, but prioritise those which contain Temperature or Dew Point Temperature values. To quote from Dunn et al, 2012:
As both temperature and dewpoint temperature are required to be measured simultaneously for any study on humidity to be reliably carried out, reports that have both temperature and dewpoint temperature observations are favoured (under the assumption that the readings were taken at close proximity in space and time) over those reports that have one or the other (but not both), even if the reports with both observations are further from the full hour. In cases where observations only have temperature or dewpoint temperature (and never both), then those with temperature are favoured, even if these are further from the full hour (00 min). All variables in a single HadISD hourly time step always derive from a single ISD time step, with no blending between the various within-hour reports. However the HadISD times are always converted to the nearest whole hour.
However, this can result in that the selected report may not include all metrics, and so there are gaps for that timestamp in the HadISD. For precipitation variables, when summing to daily, monthly, or annual totals, this will result in an apparent undercatch, where totals are lower than derived from other data sources (e.g. GSOD, also based on ISD). We've also been made aware that the logical QC check being applied to the precipitation data is not always working as intended - so it may be worth looking in the flagged_values field of the netCDF files if something looks awry.
Finally, in case you'd not seen, version 1.0.0 of GHCNh is available for download at NOAA.
