Trade figures are expected to swing around in the next few months as significant events such as the drought and the volatile currency affect the balance.
Official figures show the widest trade deficit for a July month in five years at $774 million, while the annual deficit has more than doubled to $1.7 billion.
The value of imported goods rose 17% in July to $4.6 billion compared with the same month last year, while exported goods fell by nearly 5% to $3.8 billion.
The increased import values were driven by the one-off purchase of eight New Zealand Defence Force helicopters worth $242 million, and petrol.
Exports of aluminium and crude oil were the main decliners.
Westpac senior economist Michael Gordon says the large deficit was partly payback for the better-than-expected balance in June but also reflects the timing of shipments.
He expects more volatility in coming months.
"You can get some big shifts due to timing and I think we'll probably see the August balance will improve again, because we won't have such lumpiness in some of the import items next time," Mr Gordon says.
"We are expecting the overall trade picture to pickup over the rest of this year as we see the dairy figures recover but looking beyond that, we're still looking for a pickup in imports of capital equipment and materials and, in particular, the Christchurch rebuild is going to be a big source of demand of that."
The trade balance was therefore likely to be less flattering than otherwise for the next couple of years, as the quake rebuild hits its stride.
