He added temperatures “are not rising very much at all, ranging from 9C to 11C typically”.
However, Mr Bett also warned on Thursday, a weather front is forecast to quickly head in from the Atlantic, bringing with it yet more rain throughout most of the country.
Again, temperatures will struggle to make it into double figures.
The BBC Weather forecaster said: “As we head into Thursday, we have this weather front heading in from the Atlantic – it still looks like most of the rain will be through the English Channel.
“There will be more cloud across southern parts of England and Wales and in the north, those showers are pushing further down.
“Those temperatures again – 9C to 11C, which is pretty chilly for this time of year.”
On Friday, Mr Bett explained “the weather calms down a bit” with the possibility of much drier weather across much of the UK.
“There is some warmer weather on the way.”
But looking ahead to the weekend, Mr Bett warned the UK would first have to endure another low pressure system coming in from the Atlantic, which will see wetter weather “arriving very quickly” across large parts of Britain.
Despite this, he forecast the South East to be relatively dry, with sunshine and temperatures rising to as high as 19C and in the longer-term nudging towards 21C.
The BBC Weather forecaster said: “There is more low pressure coming in from the Atlantic, pushing with it come weather fronts that will bring some rain from the southwest.
“That wetter weather could be arriving very quickly in Northern Ireland and Wales, and then heading its way northwards into northern England and Scotland.
“But there isn’t much rain towards the southeast of the UK – some southerly winds will give a bit of warmth and sunshine, and temperatures could reach 19C.”
Mr Bett also highlighted a “pressure pattern long term” in the Atlantic, explaining “this sort of pressure you are trapped with an area of low pressure close to the UK.
In further good news heading into next week, he said: “It’s not going to move very far and the winds will become lighter.
“There are some showers and longer-term rain around, but temperatures are going to be higher, perhaps up to 20C or 21C.”