I wasn't there this day, but as far as I remember:
SIN can be very rainy in TS, but it goes by quickly. They might have planned to taxi on the runway and then check their radars. Most of the time I was there, the XXTS was away earlier than I could roll on the RWY.
There are wind shears sometimes, but they are never that extreme like in the northern hemisphere. Biggest problem is the heavy rainfall taking away your visibility. If you stay low out of the cells, you might escape the red thingies on the radar.
But, as I mentioned, I wasn't there, so I couldn't decide...
Dani