Stormy Weekend In The North

A developing low pressure system in the Tasman Sea is set to take shape during Friday, gathering moisture from the subtropics as it steadily moves towards the North Island. While this low is not expected to deepen significantly, it will nevertheless deliver some intense and potentially disruptive downpours due to embedded thunderstorms within the system.

Below are two rainfall maps illustrating the predicted patterns for Saturday. On the left side, you will find the rainfall projections from the European global model, while on the right is our local New Zealand model. Although these models, along with several others we consider, have not yet arrived at a definitive rainfall total, keeping in mind that we are still a few days away from this impending event. There is a clear indication across the board that some significant rainfall could be on the way for many regions of the North Island, particularly from the Central High Country extending northward.

It is important to note that the above rainfall totals may not take into consideration the possibility of heavy downpours occurring this far out from the actual event. Therefore, we advise users to use these rainfall maps as a guide only, and to continue checking our Significant Weather Outlook page as this low-pressure system develops further in the coming days. Staying informed will help you prepare for any potential weather impacts.

Thunderstorms Explained

Convective available potential energy, commonly referred to as CAPE, is a scientific formula that is used to gauge how much ‘fuel’ is present in the atmosphere for the potential generation of thunderstorms. This particular measurement is one of many crucial factors to take into consideration when accurately forecasting thunderstorms. Generally speaking, the higher the CAPE value, the more likely it is that thunderstorms could potentially occur.

This map illustrates the CAPE values predicted for Saturday. In the context of New Zealand, thunderstorms typically last for a much shorter duration compared to those in many other countries. This is largely attributable to our relatively small landmass and our general geographic location in relation to the tropics and Antarctica. These contributing factors collectively result in the value of CAPE for thunderstorm development being significantly lower than in other regions. For example Thunderstorms could develop around 200 J/kg if all other variables align.