The MetService has issued a severe weather watch with heavy rains expected to lash the Coromandel on Wednesday and Thursday.

A frontal system over the Tasman Sea is expected to move slowly east over New Zealand from tomorrow and is preceded by a strong northerly flow bringing periods of heavy rain and gales.

The MetService says heavy rain is likely to strike the Coromandel Peninsula from Wednesday afternoon through to Thursday.

'People are advised that this is a developing situation and…parts of this watch may be upgraded to a warning.”

MetService issues a severe weather watch whenever there's an expectation conditions may deteriorate within 24-72 hours to the thresholds specified for the issue of a severe weather warning.

A severe weather warning is issued if there's widespread rainfall greater than 50 mm within six hours or 100 mm within 24 hours, and widespread gales with a minimum mean speed of 90 km/hr or frequent gusts exceeding 110 km/hr.

This latest severe weather watch will be reviewed on Tuesday at 9pm.