Taken from the Met Office: we are predicting some high temperatures and the potential for heavy rain / thunderstorms as we approach the end of this week into the weekend.
Thursday may start cloudy but the cloud is likely to break to give some sunny spells later the morning. Temperatures are expected to rise during the day, perhaps reaching 26-27C and it will feel very humid.
Friday is likely to start largely dry and fine but again feeling very humid. There is a good chance that it will turn out to be the hottest day of the year so far with the potential for temperatures to reach 30-32C.
A Heat Health Watch Level 2 heatwave warning covering London has been issued for Friday and Saturday. The high temperatures could lead to some isolated, very heavy showers and thunderstorms during the afternoon and evening. At the moment there is still much uncertainty exactly where these will develop and therefore whether there are any significant impacts. Due to this, no alerts have been issued for Friday yet but they may still be needed as confidence increases.
Friday night and Saturday are of greater concern. Very warm, moist air is expected to spread from the south on Friday night into Saturday with heavy thundery showers developing. Where these occur, torrential rain could lead to some treacherous driving conditions, significant surface water flooding, road closures, river flooding in fast responding London urban catchments and some property flooding. There may also be impacts from lightning such as localised power disruption and large hail and gusty winds may be additional hazards. Aviation/airport services may be affected too.
The Yellow RAIN Alert (Low Likelihood of Medium Impacts) issued yesterday has been updated. There is now increasing confidence that we will see heavy thundery showers occurring somewhere but where they are most likely to develop is still uncertain. The warning may be updated again as confidence increases. Details of all warnings can be viewed on the Met Office website at http://www.metoffice.gov.uk/public/weather/warnings/#?tab=map. The latest Flood Guidance Statement from the Flood Forecasting Centre also remains Yellow for surface water and river flooding on Saturday.
The showers will gradually clear from the south during Saturday afternoon and evening. Sunday is expected to continue very warm but feeling a little less humid, although isolated heavy showers are still likely to develop. Monday will still see further showers but generally less heavy and widespread than Sunday.