In the wake of Hurricane Irma Goldman Sachs has revised down its forecasts for US economic growth prompting speculation that interest rates could stay on hold for longer.

The pace of US interest rate hikes has a big influence on the value of the New Zealand dollar, our sharemarket and, to some extent, our mortgage rates.

So while there are numerous factors at work - the natural disasters could see local mortgage rates staying low for longer.

Goldman Sachs has downgraded its outlook for US third-quarter GDP growth by 0.8 of a percentage point to 2 per cent, based on an expected slowdown in business activity due to damage from Hurricanes Harvey and Irma.

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That could see the US Federal Reserve keep interest rates on hold for the rest of the year, some US commentators say.

The Fed has hiked rates twice already this year and market expectations were for a third move in December.

In July the Federal Open Market Committee voted to hold the target rate to a range of 1 per cent to 1.25 per cent.

It meets again this month but the market had not expected another hike until December.

With the minutes of the July meeting suggesting there was already a split on whether to move in December, the hurricane effect may be enough to keep them on hold.

If US rates don't rise as the market had expected that would have the effect of pushing up the kiwi dollar relative to the US currency.

It would maintain the enthusiasm of investors for equity markets - still trading at record levels - and would also keep the cost of international borrowing lower for New Zealand banks.

Local banks are reliant on overseas funding for a large proportion of their mortgage lending.

So despite New Zealand's official cash rate being on hold at 1.75 per cent, and likely to stay their for at least a year, movements in international rates have a large bearing on what we pay for our mortgages.

Goldman Sachs has estimated that Hurricane Irma will cost US$30 billion (NZ$41b), on top of US$85 billion of damage caused by Hurricane Harvey.

"The uncertainty around all of these figures is high, but there is little doubt that the combined impact of Harvey and Irma will be particularly severe," Spencer Hill, an economist at Goldman, wrote in a report. "We continue to expect a sizeable drag from hurricanes on Q3 growth."

While the damage costs don't directly come out of GDP projections they offer an indication of the scale of economic disruption around the events.

Goldman expects that consumer spending, the property market and the energy sector will all be hit by the disasters.