"This means there's a very fine line between dry weather and wetter weather and so the forecasts may change a bit as we continue to fine tune the data," said Mr Duncan.
At this stage, Sunday was the most likely day for rain as the area with rain and showers moved southeastwards.
However, this could easily change as there was an atmospheric tug-of-war between high and dry and wet and cloudy.
Brisk easterly winds were also expected to blow across the island for a time.
He said a weak front bringing wet weather to the far south would disintegrate as it tracked up the island on Sunday.