A large newly developing low is expected to bring heavy rain and gales to northern and eastern parts of the North Island over the next couple of days reports WeatherWatch.co.nz.

The low, which will form north-east of Bay of Plenty, is likely to feed heavy rain into eastern parts of East Cape and Hawkes Bay while strong to gale force south easterlies affect regions north of Taupo, including Auckland and Tauranga.

Head weather analyst Philip Duncan says the low itself isn’t going to be especially nasty but with a very powerful anticyclone over the South Island the isobars will be squeezed together. 

“The high west of the South Island currently has a central air pressure of 1045hPa which puts it in the very top end of strong highs – the low will only have a central air pressure of about 1005hPa but that is still a very steep air pressure gradient between the two systems”.

Mr Duncan says air pressure is a bit like topography, the steeper the gradient the stronger the winds.

MetService is also watching the pressure system closely issuing a Severe Weather Watch – the step before a warning – on Monday.

“A low is expected to deepen just north of New Zealand on Tuesday. During Tuesday, the cold southerly flow over the North Island will turn easterly with much warmer moist air reaching Gisborne and Hawkes Bay Tuesday evening. For Gisborne rain is expected to set in Tuesday evening and continue for much of Wednesday” says the crown forecaster.

“For Hawkes Bay, rain is expected to become widespread during Wednesday morning, and continue through Wednesday into Thursday morning. For both of these areas heavy falls look increasingly likely and it is expected this watch will be upgraded to a warning closer to the event”.