According to the ROAD TRAFFIC ACT (CHAPTER 276, SECTIONS 114 AND 140) ROAD TRAFFIC (EXPRESSWAY TRAFFIC) RULES, Stopping on road shoulders or verge is restricted to only these situations:

(a) by reason of a breakdown or mechanical defect or lack of fuel, oil or water required for the vehicle;

(b) by reason of any illness, accident or emergency;

(c) to permit any person in or on the vehicle to recover or remove any object which has fallen on the expressway; or

(d) to permit any person in or on the vehicle to give help to any other person in any of the circumstances specified in this paragraph,

the vehicle shall, as soon as is practicable, be driven or moved off the carriageway to the shoulder or verge on the left or near side of the vehicle.

Thus, you will get fined or receive 4 demerit points or both in the event that you are found stopping on the shoulders due to the weather. Hence, the best thing to do is to move over to the 3rd lane which is also the slowest lane and travel at a slower speed so as you could reach your destination safely. Or you could find a nearest carpark that you could stop for awhile to let the rain subside before continuing your journey.