Meteorological autumn has officially arrived, and already the leaves are starting to turn.
But Niwa forecasters say the odds favour a warmer and drier-than-usual autumn for many parts of the South.
On the West Coast, Southern Alps and foothills and in inland Otago and Southland temperatures are most likely to be above average and rainfall totals are about equally likely to be below normal or near normal.
Niwa National Climate Centre forecasting principal scientist Chris Brandolino said periods of ‘‘unusual dryness’’ were likely and would be interspersed with periods of rain.
‘‘Unusual dry spells can be expected at times, especially early in the forecast period.’’
He said soil moisture levels and river flows were about equally likely to be below normal or near normal.
Along coastal Otago, temperatures were about equally likely to be above average or near average, rainfall totals were about equally likely to be above normal or near normal and soil moisture levels and river flows were most likely to be near normal.
Mr Brandolino said ocean waters in February remained much warmer than normal around the South Island and marine heat wave conditions continued over extended areas off the west and east coasts of the South Island, as well as in Cook Strait.
‘‘Model guidance generally suggests that near normal to above normal ocean temperatures are likely, especially around the South Island, during the March-May 2025 period.
‘‘That is, the current sea-surface temperature (SST) anomaly pattern is expected to persist.
‘‘Niwa will continue to monitor the situation.’’
He said February’s oceanic and atmospheric conditions remained broadly consistent with a weak La Nina.
‘‘The ocean and the atmosphere in the tropical Pacific are not strongly, nor consistently coupled, contributing to the general weakness of this event and some of its unusual characteristics.
‘‘La Nina-like signals in both the ocean and the atmosphere have weakened significantly very recently.’’
Mr Brandolino said international guidance indicated about a 65% chance for the tropical Pacific to transition to El Nino-Southern Oscillation-neutral (Enso) conditions during the next three months.
‘‘Overall, a mix of anticyclonic flows and easterly quarter flows are expected over New Zealand over the autumn season.
‘‘While long-range Enso forecasts tend to be less reliable as one enters the autumn season, the guidance available suggests the possibility of re-emerging La Nina conditions next summer.’’
