We are seeing the influence on our weather of the “Sudden Stratospheric Warming” events that occurred over Antarctica during July and August. The phenomenon has the effect of pushing an unsettled westerly flow over New Zealand, from which Hawke’s Bay can be sheltered at times by the western ranges. The upshot so far is that July had below normal rainfall across the region, reaching 75% of the month’s long-term average. August delivered a near perfect 102% of the month’s average rainfall but the Heretaunga Plains and Northern Hawke’s Bay were two areas that missed out and were below average for the month. The end of September is almost upon us and we have received only 50% of average rainfall for the month. The Heretaunga Plains could therefore clock up three consecutive months of below normal rainfall.
Soil moisture levels are holding up quite well nonetheless, with many sites sitting near median levels for the time of year. Groundwater levels were near or above normal at the end of August and similarly river flows. Air temperatures were balmy in August, especially daytime temperatures which were 1.5°C above average.
A La Niña event is still possible but hasn’t eventuated just yet and is expected to be relatively weak if it does. The Indian Ocean Dipole is expected to remain neutral and not majorly influence our weather. Sea surface temperatures are warmer than usual around New Zealand.
The predicted sea level pressure pattern for the next three months has an area of higher than normal pressure extending over New Zealand from the east and south, which suggests a switch from the current westerly regime to a northeast wind flow. The warm sea temperatures should aid continuation of warm air temperatures, while rainfall forecasts are mixed amongst the forecast models but mostly settle on near normal rainfall over the three-month period. My bike rides in the blustery westerlies have been hard going and borderline wild at times, so I’ll be quietly thankful for a respite.
All the best,
Kathleen
