Firefighters at the huge forest fire outside Nelson are working against the clock to control the fire before forecast strong winds arrive tomorrow.
The fire this morning had covered 1900ha with a 22km perimeter. On Tuesday it quickly swelled to from just under 900ha to more than 1870ha within about three hours.
Tasman District Mayor Richard Kempthorne said yesterday's conditions were a big improvement.
"We had a roaring fire two days ago and it was impossible to control and protection of people and properties was paramount."
"Yesterday the wind direction turned ... it was a much calmer day, mild breezes and much more effective for firefighting," Mr Kempthorne said.
Fire and Emergency incident controller John Sutton said it was the milder conditions which allowed firefighters to keep it from spreading.
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"It didn't progress anywhere in its perimeters yesterday but that's more to do with the benign conditions and work we were doing directly on the perimeter," he said.
He said wind was firefighters' biggest enemy.
"When fire goes through the landscape it doesn't go with a clean sweep ... you end up with islands of unburnt fuel that's still actively burning.
"The thing that rapidly will spread a fire is the ember transport (embers carried by the wind)."
The calm weather is expected to hold today - with even less wind and high of 20C predicted by MetService - however the high winds are expected to return tomorrow.
Mr Sutton said he hoped to have the fire under control by then.
"The forecast for tomorrow is not good for firefighting. As you'll probably appreciate wind is our enemy and wind is what transfers fire the quickest."
"The message for you today ... today is a huge day for us.
"Let's hope that it continues through the day as predicted.
"We have to be prepared for what's probably going to hit us tomorrow ... it might not happen, but we have to be prepared for that."
He said the fire was still out of control.
"We have not got a containment line around the entire fire. I'm hoping by the end of the day that we'll be in a lot better position.
"When I talk about containment, that means there has to be no embers or active heat within 30 metres of the actual perimeter."
He said they would carry on "hardening" the external perimeter of the fire at a higher rate.
"There's 22km of perimeter on that fire at the moment ... our job is to keep it within that perimeter from now on.
"There's over 100 firefighters on the ground today, that's a major increase, that's twice what we had before."
He said more lines of fire retardant material would be laid by planes today.
Mr Sutton seemed confident however they had what they needed.
"We're reasonably comfortable that we've got a good allocation of resource, but we know as the civil defence minister said yesterday we know who to call if there's anything we need."
A long, dry spell
While wind is the problem now, the fire comes on the heels of a long warm, dry spell in the Nelson region.
"The start to summer was the third warmest on record for New Zealand," said Niwa meteorologist Ben Noll.
"The warm pattern has been a result of very warm sea surface temperatures both in New Zealand coastal waters and in the Tasman Sea as well as a lack of cooler southerly winds.
He said Nelson has recorded just 84mm of rain between 1 December and 5 February, far short of the usual 224mm that normally fall between the beginning of December and the end of February.
"As of 6 February, Richmond (Tasman District) was on a 22-day dry spell," Mr Noll said. A dry spell is defined as less than 1mm of rain on consecutive days.