The Met Office has placed Newport under a weather warning, with heavy rainfall forecast for Friday.
Conditions are expected to deteriorate at midnight, when the probability of precipitation reaches 95 per cent.
Rain will continue during the early hours, with heavy falls lasting until 7am.
At 8am, the forecast indicates a short-lived break in the heaviest rain, followed by lighter drizzle.
Temperatures will remain near 10C throughout this period, although wind will make the apparent temperature closer to 8C.
North-north-westerly winds are forecast at 10mph, with gusts of up to 29mph.
During Friday afternoon, the rainfall is expected to ease and sunny spells are likely from 4pm.
The temperature will stay at 10C, while the apparent temperature will fall to 7C.
Winds will shift to the west-north-west and strengthen to 21mph, with gusts reaching 44mph.
By evening, the forecast is for partly cloudy conditions and a temperature of 9C.
Gusts are expected to ease slightly to 34mph.
Overnight, skies will become clear, with temperatures falling to 8C.
West winds will continue at 11mph, accompanied by gusts of up to 33mph.
Saturday begins with clear skies and a temperature of 8C.
West-south-westerly winds will blow at 8mph, with gusts reaching 26mph.
Cloud cover is expected by 4am, when the forecast also calls for light rainfall.
The rain will intensify later in the morning, with a 95 per cent chance of precipitation from 8am.
Temperatures will climb to 10C, although they will feel more like 8C.
South-south-westerly winds will continue at 8mph, with gusts of up to 27mph.
Heavy rain is then expected to persist through the afternoon, as temperatures rise to 15C.
South-westerly winds will reach 21mph, with gusts of up to 47mph.
The rainfall should begin to ease during the evening, although light showers are forecast until 10pm.
The temperature will be 14C, with an apparent temperature of 10C.
West-south-westerly winds will continue at 22mph and produce gusts of up to 48mph.
Partly cloudy conditions are expected overnight on Saturday, with temperatures dropping to 11C.
Winds will remain westerly at 18mph, with gusts reaching 44mph.
Sunday is forecast to begin with light showers and a 60 per cent chance of precipitation.
Temperatures will be around 10C, although the apparent temperature will be 7C.
West winds will blow at 20mph, with gusts reaching 42mph.
The showers are expected to stop by 6am, giving way to sunny intervals for the remainder of the day.
The temperature will rise to 12C, while feeling closer to 9C.
West winds will continue at 20mph, with gusts of up to 42mph.
Partly cloudy conditions are expected in the evening, when the temperature will fall to 9C.
Winds will then veer west-south-west at 11mph, with gusts reaching 23mph.
Monday will open with cloudy skies and a temperature of 9C.
From 6am, the forecast predicts light rain and a 60 per cent chance of precipitation.
The rainfall is expected to become heavier as the morning continues, with the chance of precipitation increasing to 90 per cent from 11am.
The temperature will reach 16C, although it will feel more like 14C.
Rain will continue through the afternoon and evening, with temperatures remaining at 16C.