But the race will go on regardless.
'F1 is a rain-or-shine event,' said a spokesman for the race organisers.
The three-day spectacle which kicks off on Friday will culminate in a final race on Sunday night at 8pm. Wet weather is likely to have the biggest effect on drivers as it affects visibility and speed.
'Every precaution has been taken to ensure a safe race,' said the SGP spokesman.
Race cars have come prepared with wet weather tyres, which have more complex groove patterns to help cars dispel water on the slippery tracks.
Helmets have rain-proof visors which prevent water droplets from collecting and impairing the drivers' vision. Drivers have also had hours of practice on simulators, to ensure that they are well prepared for Sunday's night race.
To further help drivers better prepare for the race, organisers have brought in weather monitoring equipment, which will track temperature, humidity and wind direction.
On the other side of the track, spectators are encouraged to leave their umbrellas at home, to prevent obstructing the view of others.
Instead, they can buy ponchos for $2 a pack. All profits will go to the Singapore Red Cross Society and St John Ambulance Singapore.
Singapore has had a wetter-than-usual September so far. Western parts of the island, like Choa Chu Kang and Tuas, received up to 275mm of rain - the highest rainfall during that period, said the NEA. The Southwest Monsoon period, which has been bringing intermittent heavy rain, usually persists into early October.
For the next fortnight, weak Southwest Monsoon conditions will continue to prevail over Singapore and the surrounding region. The low-level winds over Singapore are expected to blow predominantly from the southeast or southwest. Hotspot counts in Indonesia crept up the past week, crossing the 200 mark. -- TANIA TAN