The UK is set for the hottest start to November since records began, forecasters say. The Meteorological Office predicts temperatures will rise to more than 21.7C (71F) on 1 November, beating the record high of 69 years ago in Prestatyn, Denbighshire, North Wales. The Met Office reports that hot air travelling over from Portugal is bringing the out-of-season heat, which is likely to make the UK warmer than the Mediterranean.

In the meantime, on 31 October temperatures are set to reach 21C, with sunshine in the afternoon. These predictions would make 2015's Halloween the second hottest ever, behind last year's peak of 23.6C at Kew Gardens, London, and at Gravesend, Kent. The exceptionally mild weather – 6C above averages for this time of year – is predicted to continue through the following week.

In a statement the Met Office said of temperatures on 31 October and 1 November: "There is a possibility that parts of south-east England could see maximum temperatures in the high teens, perhaps touching 21C-22C. The extent and degree of warmth will be affected by how much cloud cover there is, which is difficult to forecast accurately three days ahead."

"However, there will be decent bright or sunny spells. On Sunday we can expect similar weather to Saturday, with many places staying dry with bright or sunny spells after mist or fog clears." Cooler conditions are expected in the north, with highs of 14C-15C in the northern towns of Manchester, Sheffield and Newcastle."

Experts are saying further record highs are likely to come in November. British Weather Services senior meteorologist Jim Dale said: "Somewhere in the UK could hit a record November temperature in the week from Sunday." But while reporting of record-breaking temperatures grabs headlines, caution is advised.

Temperature records began relatively recently, with reliable statistics dating back only to 1914. This means that only a vanishing fraction of weather history in the UK is documented. Philip Eden, a weather historian, is critical of reporting of weather records. He told the Guardian newspaper: "Saying it is 'unprecedented' allows the people who look after our infrastructure a ready-made excuse for not being able to deal with [extreme weather]."

Meanwhile, the West Country has been hit by flooding. Coastal towns and villages in Cornwall found themselves inundated as spring tides washed over barriers. The Environment Agency has issued a series of flood warnings and alerts across the UK for 31 October. However, forecasters predict the weather going forward should be calm and dry.