Civil Defence Whanganui's Tim Crowe said he and other duty staff received an alert once the river level rose above six metres in the catchment.
Crowe said once the alert was sent out Civil Defence staff examined the water levels in the river and forecasts along the river to assess whether it was likely to flood.
However, Crowe said river levels above 6m at Pipiriki were relatively common, usually occurring around 10 times a year.
"It doesn't mean a flood, for us, it basically lets us know there's a bit of rainfall going into the system," Crowe said.
Looking further into the week, Parkes said more rain was expected for Whanganui and most of the country.
After the relatively fine weather experienced on Wednesday, Parkes said conditions were expected to deteriorate through the rest of the week, with possible gale-force winds developing on Friday.
Rain was expected to develop again on Thursday and continue through the week, beginning to clear on Sunday.
Crowe said with the extra rainfall expected, Civil Defence forecast river levels at Pipiriki to reach 7m to 7.5m.
However, Crowe said it would not be enough to cause the river to flood.
"It won't flood, the main river won't flood unless we get something significant.
"For it to flood down here in Whanganui, you're looking at over 12m or higher at Pipiriki."
During the last major flood of the Whanganui River in June 2015, Crowe said it peaked at 15.5m at Pipiriki.
Crowe said the 2015 flood happened after three days of consistent rain across the region and it would take a similar weather event to cause another flood.
Crowe said since 2015 Civil Defence had adopted a cautious approach when the river began to rise and communicated with communities in low-lying areas along the Whanganui River Road if Pipiriki reached 6ms and was expected to go higher.
