The next South Pacific tropical cyclone may form this week about 2000 kilometres from New Zealand, but it won't be an easy journey for it to reach New Zealand.
WeatherWatch says long-range global modelling has been showing for days a tropical storm is forming - or there are some low-pressure zones - sometime this week as low pressure shifts from the Coral Sea area towards New Caledonia.
The storm - or tropical low - will then drift towards New Zealand, but unlike Cyclone Dovi, this low-pressure zone has a more complicated journey due to powerful high pressure over southern New Zealand.
"Storms and lows weaken when they run into high pressure, especially powerful high pressure, so the stronger the southern high is then the lower the chances are of this potential storm making it to New Zealand," says WeatherWatch head forecaster Philip Duncan.
"Most modelling suggests the low will lie north of New Zealand then it may struggle to come further in to land, meaning a windy easterly 'squash zone' of air pressure may set up for the top of the country later this week, but damaging winds and stormy weather overall may be less likely on land and more likely out at sea."
WeatherWatch says the week ahead is likely to be drier than average for most of New Zealand since high-pressure zones are moving in. But if the low does track in close enough, windy easterlies along with dangerous marine conditions can be expected, with WeatherWatch adding that some modelling shows northern New Zealand is within the "cone of uncertainty".
When ex-tropical Cyclone Dovi hit the North Island earlier in February, it dropped down from the same area as this next low is forming in. But Dovi tracked in southwards very quickly as there was a "gap between highs", WeatherWatch says, allowing a natural set-up for Dovi to be funnelled down southwards towards the North Island with limited obstacles.
"For this next tropical low the high-pressure zone looks to be centred over southern New Zealand and that acts like an invisible brick wall in the sky to really slow down storms, a bit like how a strong sea wall stops big storm waves from advancing on to land," Duncan says.
Forecasting from MetService says that the likelihood of a tropical cyclone forming near New Caledonia before Tuesday is low, as is the chance of a second tropical disturbance found in the Coral Sea that is moving southeast.
But these two tropical disturbances are expected to merge into one system near New Caledonia on Tuesday.
"There is a moderate risk of this merged system developing into a tropical cyclone on Tuesday or Wednesday before conditions become unfavourable on Thursday," MetService says in its Tropical Cyclone Bulletin.
