Nelson is so desperate for a rain radar that it's installing a ship radar because the Government won't fund a proper MetService one in the region.
It's the first time a ship radar has been used in this way in New Zealand and is expected to save lives in future floods.
The radar is typically used on ships to detect other vessels, but the $25,000 system can also detect rain.
So Nelson-Tasman councils are installing it near Mapua to fill the gaps in their flood warning network.
"It's really an act of desperation," said Tasman District Council's principal hydrologist Martin Doyle.
He believes this is the first time it's been used as a rain radar, but is confident it'll work.
"It'll work for certain types of rainstorms, and there's one key one where we have embedded rain storms tracking in one after the other - exactly as we saw in Auckland in January," he said.
The marine radar should give the council one-two hours' warning.
"This warning time is a valuable head start when responding to flooding," said Doyle.
For 13 years the councils have been trying to get a proper MetService rain radar, but it costs up to $5 million and after being repeatedly declined they decided it was time to get creative.
Nelson Mayor Nick Smith is beyond frustrated and told Newshub the marine radar is just a temporary, and desperate, measure.
"We've gone for a very sub-optimal Kiwi, do-it-yourself, marine radar to try and make the best of a bad situation," he said.
The Nelson-Tasman region is on the outer range of MetService's big rain radar on Wellington's south coast, and Doyle said that makes it challenging to accurately detect heavy cells of rain.
Intense convective cells of rain, often associated with thunderstorms, can slide between rain gauges undetected, and he said the worst situation is when a series of convective rain cells follow each other down a path and create ongoing intense rainfall in one location.
It means in events like the Nelson flood last year, and the flooding in May, it can be hard to get quick and specific data to inform evacuation decisions.
"It's been a longstanding problem for us that we don't have a radar," said Doyle.
Especially because the region is vulnerable to weather from all directions, which can cause damaging and dangerous floods. Doyle said when Cyclone Gabrielle wiped out the rain gauge network on the East Coast it was a wake-up call.
"It's really made us do some soul-searching of what would we do in that situation. We need access to good quality data and modern technology," he said.
MetService manages and installs the radar network in New Zealand through a contract with the Ministry of Transport. Its chief executive Stephen Hunt acknowledges there are some gaps in rain data for Nelson.
"Because of the curvature of the earth and masking by the mountains, they do miss out in some of the lower level areas," Hunt said.
The Minister for Transport, David Parker, declined Newshub's request for an interview. He said in a statement that MetService's priority is maintaining its current network of rain radars around the country and it has completed work on upgrading the Wellington one.
However, he said extending the network "will be subject to additional funding, with Nelson-Tasman a high priority".
But that might not be until 2028.
"We'd expect those areas and regions to be on the next iteration of the plan, but it could be brought earlier with additional funding," said Hunt.
However, he said a rain radar is just one tool.
"A rain radar is not going to on its own be the solution, it'll be part of a better solution for Nelson," he said.
That's not good enough for the mayor, who's urging the Government to invest in a rain radar for Nelson-Tasman so the area can be better prepared for the inevitable increase in flooding events.
"It's a no-brainer and it's a disgrace that we can't get the funding to improve this resilience of our community to such storm events. It also frankly means a better chance of saving lives," said Smith.
