Rainfall of more than 20mm an hour is being forecast for parts of Hawke's Bay in the midst of the 30th anniversary of Cyclone Bola as weather deteriorates in the lead-up to a possible date with another tropical cyclone.

Although nothing as extreme as the conditions that washed away the concrete centre span of the Wairoa Bridge at 6am on March 8, 1988 is predicted, the Metservice yesterday had a severe weather watch in place for Wairarapa to Central Hawke's Bay, and there was some hint of rainfall as much as 200mm in the hills and ranges of Northern Hawke's Bay in the 12 hours to midday today.

Up to 30mm of rain was forecast for Napier, Hastings and Central Hawke's Bay overnight to 8am today.

The first hints of a wet week came with what a Metservice forecaster called a "thunderstorm cell", which brought 28mm of rain to Napier in an hour early on Tuesday night.

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The 41.6mm of rain recorded for the whole day in Napier was equal to about two thirds of the March average for the city and contrasted with the less than 1mm recorded in Hastings, but the meteorologist said there were other isolated bands of wet-weather in the region, including some hail.

It was the first significant rainfall recorded in Napier in more than three weeks, although 2mm was recorded on February 26.

The regional forecast for today was rain, heavy at times, especially about the ranges, with possible thunderstorms in the afternoon and southeasterlies, strong in exposed places.

Heavy rain was forecast through to tomorrow afternoon, easing to occasional showers in the afternoon, with continuing southerlies, strong in exposed places.

Metservice's severe weather watch covers the 41 hours from 4pm yesterday to 9am tomorrow, and says periods of rain were expected from late Wednesday afternoon through to early Friday.

The latest threat from the Pacific is Tropical Cyclone Hola, named in Fiji early yesterday. Damage has already been reported in Vanuatu and the storm is expected to reach a peak late tomorrow and on Saturday. It will possibly touch the upper North Island by the end of the weekend.

A year ago parts of New Zealand, mainly from Auckland to the Coromandel Peninsula, but also including Hawke's Bay were in the throes of a storm that became known as the Tasman Tempest.

Rainfall in much of Hawke's Bay and the Gisborne area in March last year was more than 50 per cent up on the March average.