South Wairarapa has been identified as a "hotspot" for soil moisture deficit, according to Niwa.
The agency's weekly Hotspot Watch says South Wairarapa is an exception to the North Island's near normal moisture range for this time of year.
The area is continuing to decrease in soil moisture levels.
Persistent hotspot regions have the potential to develop into drought.
Elsewhere, Hawke's Bay is benefiting from widespread and heavy rain during September, making levels wetter than normal.