Wet in the west, but a rest in the east

July 24, 2017

July has been marked by severe weather events, caused by low pressure systems from the Tasman Sea.  Strong westerly winds have stayed to the south, allowing lows to develop and linger resulting in significant rainfall.  This week sees a brief return to normality, as westerlies move north and the weather takes a more mobile turn. A series of fronts bring rain to the west, but allow the east a chance to dry out.

The westerlies bring showers to the North Island, some of which could blow up into thunderstorms for the upper North tonight and tomorrow, bringing 10-20mm in an hour for a few spots. Otherwise Tuesday and Wednesday look to be the pick of the week, with plenty of sunshine for both Islands.
The spell breaks towards the end of the week, when another low crosses central New Zealand.  This will bring more rain to the West Coast on Wednesday, before a southerly runs up the Canterbury coast on Thursday bringing another spell of rain.

“Although unlikely to reach official warning criteria”, said meteorologist Tom Adams, “the already saturated ground in the Canterbury and Otago area means that our forecasters will be watching this very closely, as even smaller amounts could lead to further flooding”.  This rain will fall as welcome snow in the Canterbury club ski fields, with lesser amounts further north and south.

The good news is that the low pressure system is fast moving, and followed up by a ridge of high pressure.  This means that rain and snow accumulations will be reduced, and by the weekend New Zealand can look forward to cool, crisp conditions with hard frosts in inland parts of the far south.

This image shows modelled rainfall accumulations for the next six days, data courtesy of UKMO.

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