The upper North Island is set for a lengthy period of heavy rain and strong wind this week, as a deep subtropical low develops west of New Zealand. MetService has placed a fresh 53-hour heavy rain watch for the Northland area from 10am on Wednesday to 3pm on Friday. A strong wind watch is also in force for Northland from 6pm on Wednesday to 6pm on Friday, with east to northeast winds approaching severe gale in exposed places. MetService said there is a moderate chance that the rain and wind watch could be upgraded to a warning. The system is expected to move into the Tasman Sea by midweek, before intensifying as it approaches the country. There is a moderate chance of rainfall and strong winds along the west coast of the country on Thursday. Photo / MetService MetService meteorologist Sylvia Martino said the system is still evolving. “What we’ve got coming up later in the week is a low coming down out of the subtropics and moving towards the northwest of the North Island,” she said. “There is still some variation between the model solutions as to exactly where that low ends up.” Conditions are expected to remain relatively settled through Tuesday as a ridge of high pressure moves away to the east, with minimal risk of severe weather. However, by Wednesday, the subtropical low is forecast to move west of the North Island, bringing rain and strengthening northeasterly winds, particularly to northern regions. By Thursday, the system is expected to intensify further while remaining west of the country, pushing bands of rain on to both islands and strengthening winds. Auckland, the Coromandel Peninsula, Bay of Plenty, Taranaki, Tasman and parts of the West Coast face a lower chance of significant rainfall. There is moderate confidence that severe gale northeasterly winds could affect parts of Northland, Auckland and the northern Coromandel Peninsula. A low risk has been put in place for other areas, including Waikato, Taranaki and Banks Peninsula. Forecasters note the exact impacts will depend on the track of the low as it moves south from the subtropics. By Friday, the low is expected to move on to the South Island, with associated rain spreading eastwards across the country. Martino said while the term may sound similar to a tropical system, a subtropical low simply refers to where the system forms. “What we’re talking about is a low that forms in the subtropics, roughly between 20 and 35 degrees south,” she said. Because these systems form in warmer regions, they can carry significant moisture, which can then be drawn down over New Zealand, increasing the risk of heavy rainfall.