Rainfall of 44.4mm was recorded at Whanganui Airport for the 24-hour period from midnight on Saturday.
It is the most significant rainfall the region has had since February when 66.6mm was recorded over Waitangi weekend.
"After the long, dry, settled weather patterns that have followed, Whanganui is now in for some changeable conditions," MetService meteorologist Lewis Ferris said.
"Although it is not going to rain constantly for the next few days, there will be plenty of showers coming through so it would be advisable to dry the clothes inside."
Ferris said a new heavy rain watch had been issued for Tongariro National Park which covered the 14 hours from noon on Tuesday to 2am on Wednesday.
"The rain bands coming through are always heavier at higher altitudes," he said.
"In the low-lying areas, they will be lighter but still significant at times."
Ferris said while air temperatures were still warm for the time of year, things were expected to cool down later in the week when a southwesterly change is forecast.
During Thursday and Friday, a broad trough is expected to sweep across New Zealand from the west, bringing unsettled weather and cooler west to southwesterly winds.