High summer or monsoon?
It may seem a little depressing to note that we have now passed the longest day. The
days may indeed be drawing in – but that doesn’t mean summer is over. July and
August often see the hottest days of the summer – but they can also be the wet months
as the heat and humidity builds.
Meteorologically speaking, summer is measured from 1st June until 31st August. By
the time you read this we’ll be about half way though this period – a period that seems
to have thrown almost everything at us. We’ve had everything from hot sunshine to
cold and wet, with some quite torrential downpours at times. In fact, the period as a
whole has seen rainfall about 25% higher than normal, though temperatures have been
mostly above average.
On average, both July and August are warmer months that June, though admittedly
2007 and 2008 gave us disappointing summer holidays. We’ve already seen
temperatures reach 28-30C across the Midlands at the start of this month, with 31.8C
logged at Wisley (Surrey) on the 2nd. This is amongst the hottest weather since 2006.
So why does it usually get warmer after the 21st June – the longest day? After all, the
sun is in the sky for progressively less time once this date has passed.
Our UK weather is not only governed by the wind direction, which prevails from the
south-west. The warmth we experience also has a close correlation with sea
temperatures – and our seas take a while to warm up. It can take until the middle of
August for our sea temperatures to reach their annual maximum, and so this combined
with a favourable wind direction and some sunshine can ensure that potential summer
heat continues well after the longest day. The opposite is true in winter: our coldest
weather is usually in January and February – after the shortest day.
Although the last two summers have seen more than our fair share of rain, it is not
uncommon for high summer heat to trigger torrential downpours. Warmer air can
hold more moisture, and so hot and humid conditions are the ideal catalyst for this
kind of weather. This sort of scenario was experienced in our last hot spell.
As is always the case with showers or thunderstorms, they are very difficult to predict,
and pinpointing their expected destinations is virtually impossible. It may seem like
the weather forecasters are hedging their bets when you hear phrases like ‘sunshine
and showers’ or ‘expect some sunshine with thundery showers possible’. But in
reality, they are just describing the situation!
Showers and storms can build up almost anywhere when the conditions are right: it
often starts with those familiar sunny mornings, with fluffy cumulus clouds bubbling
up into towering cumulonimbus by the afternoon bringing torrential downpours.
Because showers and storms like this develop in a different way to ‘frontal’ rain which covers a wide area and is the boundary between two air masses - it means that
some places stay dry in between developing showers. People who miss out often think
the forecast has gone wrong and wonder what all the fuss is about!
So next time you’re watching the forecast and ‘showers’ are mentioned, you may or
may not get wet. Better to be prepared just in case, though! At least there is still time
for another heatwave…