As Jersey enjoys (or endures) one of the hottest periods of weather for 20 years, we asked Jersey Met some important questions, like: Why is it so hot? Is it ever going to rain again? And why is Guernsey so much cooler than us?
1. It has been very hot recently, but are we actually having a heatwave?
We use the World Meteorological Organisation (WMO) definition of a heatwave which is ‘a period of more than five consecutive days when the maximum temperature exceeds the average maximum temperature for that day by five degrees Celsius’. The average maximum temperature for each day is calculated from the 30-year period from 1981 to 2010.
Today (Wednesday) will see us record five consecutive days with a maximum temperature 5°C above the average for each day. However with a much lower maximum forecast for Thursday, we are not likely to record a meteorological heatwave.
2. When was the last time it was so hot for so long?
The last time the Island recorded a meteorological heatwave was in May 1995. Looking back through our historical records which began in 1894, we have only recorded this on six occasions.
3. And what has been our longest ever heatwave? Was it the sizzling summer of 1976?
Yes, the longest heatwave period on record was in June/July 1976 – 13 days.
4. What is the hottest June day on record?
The hottest June day on record was 30 June 2015 when we recorded 33.0°C at the Maison St Louis Observatory. Official records for the Island are taken from the observatory where records began in 1894.
5. And what was the hottest ever day in Jersey?
The hottest day on record was 9 August 2003 when we recorded 36.0°C at the Maison St Louis Observatory.
6. What is causing these extreme temperatures?
Hot air over the continent is being drawn over the Island from an easterly direction. At this time of year the energy from the sun is at its maximum and with no cloud each day we see a gradual increase in daily temperature along with very high night-time temperatures.
7. How hot has it been in nearby France?
35.4°C was recorded in Rennes on Tuesday afternoon.
8. And when is the heat going to subside?
During Wednesday night the temperature is going to fall to around 14°C which is some 5°C to 6°C lower than recent night-time temperatures. We are currently forecasting a maximum temperature of only 21°C on Thursday which is average for this time of year but 10°C cooler than Tuesday.
9. We’ve forgotten what rain looks like. When are we going to see some?
There is the chance of some rainfall on Saturday although amounts are likely to be only small. The thickening cloud on Friday may just give us a spot or two of drizzle.
10. And finally, why is Guernsey so much cooler than us at the moment?
Guernsey has had hot temperatures over the last few days, although a little lower than here in Jersey. Guernsey is generally cooler than Jersey because it is smaller, it slopes from south to north (Jersey slopes north to south) and it is further away from the continent therefore the air is cooled as it travels over the sea. Sea water temperatures around Guernsey are lower at this time.
