The forecaster issued the first yellow weather warning this morning (September 3), which is in place from 11am to 8pm.
It is in place across South Wales, including Blaenau Gwent, Caerphilly, Carmarthenshire, Monmouthshire, and more.
The second is in place across the majority of Wales tomorrow, from 2am to 5pm.
Residents have been warned of delays to travel, as well as heavy showers, thunder, strong winds and potential flooding.
Here is all to know about the warnings and how to prepare for them.
The Met Office said the new weather warning has been issued across South Wales due to the predicted thunderstorms and scattered heavy showers which "may cause some impacts during Wednesday".
Detailing the forecast for this afternoon, the Met Office says: "Scattered heavy showers, some with thunder, are expected to develop later this morning and into the afternoon, before easing this evening. In the most active storms, hail, strong gusty winds, and lightning may be impactful.
"There is also a chance that a few spots could see frequent, heavy bursts of rain, leading to surface water flooding."
Tomorrow, expect similar heavy showers and thunderstorms; however, the Met Office adds that the impact is less likely.
The full list of places affected by the weather warning in Wales today is as follows:
The full list of places affected by the weather warning in Wales tomorrow is as follows:
The Met Office recommends preparing a flood plan and an emergency flood kit if your location is at risk of flash flooding.
It also urges you to check road conditions if driving, or bus and train timetables, amending your travel plans if necessary to avoid delays.
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A spokesperson adds: "People cope better with power cuts when they have prepared for them in advance. It's easy to do; consider gathering torches and batteries, a mobile phone power pack and other essential items.
"If you find yourself outside and hear thunder, protect yourself by finding a safe enclosed shelter (such as a car). Do not shelter under or near trees, or other structures which may be struck by lightning. If you are on an elevated area move to lower ground.
"Be prepared for weather warnings to change quickly: when a weather warning is issued, the Met Office recommends staying up to date with the weather forecast in your area."