If you look up the weather forecast now for Bangkok, Thailand, you will find there literally is a forecast for a 50 % chance of isolated thunderstorms every day.
When I wake up at 5 am to go on my rides, I generally listen for thunder and flashes of lightning in the direction of my ride before getting dressed. When I am about to leave the house at 6 am, it is day break and I try to see if there are storm clouds in the direction of my ride. On the drive to my loop, I ignore the rain, if there is any, because I figure that the isolated thunderstorm is not raining at my loop - this actually not wishful thinking because the thunderstorms here are really, really isolated. At my riding loop, unless it is raining, I start riding. The isolated nature of the thunderstorms here are amazing - in my 10 mile loop, it is quite common for a 2 mile stretch to be completely flooded and another stretch to be bone dry. Even if it rains while I am riding, I continue unless the storms are so strong that I can not literally continue - a couple of times not only were the motorcycles pulling over and stopping, but the vans were too, and I just stood in the middle of the rain and took it like a man.
Mark