A developing low-pressure system will introduce a series of weather fronts to southern parts of the UK in the afternoon. The warm front will bring a warm theta-E air mass to most of southern England in the evening. Due to significant horizontal wind shear at lower altitudes, the resulting thunderstorms will move slowly and have a relatively short lifespan. The gradual storm movement will cause the downdraft to intersect with the updraft, leading to a slight reduction in storm intensity. Within the moisture-rich environment where these storms form, intense rainfall may occur, albeit briefly.
During the late afternoon, the warm front may trigger thunderstorm development behind itself due to unusually high 3CAPE (>200 J/kg), maintaining their thundery nature over central southern England due to moderate low-level and mid-level wind shear. Slow-moving storms could lead to significant rainfall and localised flooding, mainly impacting central southern England, specifically Dorset, Somerset, and Wiltshire. Some of these storms may sporadically produce lightning. However, limited Convective Available Potential Energy (CAPE) and a saturated profile across the north of M4 will restrict activity, causing thunderstorms to decay into heavy rain.
Additional thunderstorms will develop behind the warm front in the early night, generating potent thunderstorms in some areas. These storms will move northeast due to the forcing from the cold front, potentially causing intense thunderstorms across southeastern England and parts of East Anglia. Strong shearing conditions increase the likelihood of isolated supercells characterized by rotating updrafts. Significant speed shear ensures swift storm movement, maintaining a separation between the updraft and downdraft. At the same time, directional shear induces rotation within the updraft, allowing these cells to produce marginally severe hail (up to 1.5 cm in diameter), intense rainfall (up to 50 mm within 6 hours), and risk of one or two brief tornadoes, especially across southeastern England. Coastal areas are likely to experience strong gusts due to the low-pressure system located at the left exit of a strong jet stream, with coastal gusts widely exceeding 50 mph and possibly reaching 75 mph in places like Eastbourne and Kent, posing a risk of localized damage. Coastal flooding may occur due to high tides and strong coastal gusts.
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