September was warm and somewhat dry, the fourth consecutive month of below average rainfall for the UK as whole. The total rainfall for the UK was 84% of the monthly average, and with an average temperature of 14.7°C, it was the second warmest September for the UK, and for Northern Ireland with 14.2°C, equal warmest with 2006 (both in series from 1910). River flows were average or below average across Northern Ireland, Wales and much of England, although above average in parts of the south-east. Groundwater levels continued to recede everywhere except in the Carboniferous Limestone of south Wales. However, levels remained within the normal range or above, and were exceptionally high in aquifers in the north-east and south-west of England. Reservoir stocks fell, and although close to average for the English Lowlands, were below average elsewhere, most notably in the north‑west of the UK. Indeed, stocks for September at Loch Thom were the lowest on record (in a series from 1993) and less than half of those typical of the month, and total stocks for Scotland dropped marginally below the minimum established in 1995. With low September rainfall compounding the effect of the dry summer in the north-west, and little indication of a wet autumn in seasonal outlooks, it is here (in contrast to the south and east where groundwater resources are healthy) that close observation will be required over the coming months.