July 2025 - Stormy Tasman Sea to influence weather this month

A LOOK BACK - While keeping a close eye on short to medium range forecasts, our forecasters also like to look ahead into possible upcoming weather trends. Late June was characterised by warmer temperatures as the weather that developed in the Tasman Sea influenced on the ground conditions across the South Island.

The first few days if July were unusually stormy and wet for the north and west of the South Island, however a ridge of high pressure is moving in for the first weekend of the month, promising settled conditions and frosty mornings.

A LOOK AHEAD - The Southern Annular Mode, also known as “Sam” is heading in the upward trajectory and will likely remain positive for the remainder of the Month. Positive SAM values typically present the upcoming weather patters coming into the country from the north and northwest - meaning more low pressure systems and unsettled weather conditions are likely to originate from the Tasman and Coral Sea. A new low pressure system is expected to develop in the Tasman Sea later in the second week of July, but unclear whether significant impacts and increased rainfall will materialise for the South Island, highest risk again in the Upper South Island.

Further frontal systems and low pressure systems are likely throughout the month, with rainfall expectations above normal for the West and North of the South Island, with equal chances elsewhere. Temperature swings are likely, and while weather systems originating from the north and west will likely be more common than normal, we are in winter and cold snaps and low snow possibilities are always possible.

Confidence Moderate for increased rainfall in the north and west. Near normal/Equal Chances elsewhere.

Confidence Low for warmer than normal for the Upper South Island. Equal chances elsewhere,