The advisory is until 6:30 p.m.
Doppler Radar indicated heavy rain from the thunderstorms, the weather service said.
Rainfall rates of 1 to 2 inches per hour are occurring in some areas.
Excessive runoff will cause ponding of water in urban areas and on highways, streets and underpasses as well as other poor drainage ares and low-lying spots.
Flooding of small creeks and streams as well as country roads is also possible, the weather service warned.
But the storms as providing relief from the weeklong heat wave. Temperatures dropped from the upper 80s into the mid-70s as the thunderstorms hit the area, according to the weather service.
Storms may continue into the evening and night-time, with patchy fog possible.
The relief won't last for long. For Friday, temperatures will be back in the upper 80s under a bright sun.
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