Met Office forecasters say thunderstorms are likely to hit Hampshire today.
They sounded a yellow warning of rain for London and south east England from midday until 10pm.
Forecasters said that after a mainly dry start with sunny spells, showers would develop during the morning.
A Met Office spokesman said: ‘These could then turn heavy and thundery in places, with some slow moving torrential downpours likely.
‘Showers will continue through the evening, only gradually easing overnight. Some clearer spells could then spread into western areas by dawn’
The forecast for the rest of the week is slightly better though.
The Met Office prediction is: ‘Any remaining showers from overnight will clear, leaving a mostly dry morning with sunny spells. However further showers are likely later, along with a fresh northwesterly breeze. Maximum Temperature 20 °C. Outlook for Thursday to Saturday: Mostly dry, with plenty of sunshine Thursday. Turning cloudier and breezier Friday, but staying dry. Cloudy start Saturday, but some sunny spells developing, and perhaps the odd shower later.’