The Emirates is braced for three days of rain, with police warning motorists to be careful on the roads.
Heavy showers fell on Dubai and the Northern Emirates on Wednesday afternoon, with more on the way.
In Abu Dhabi, authorities told residents to "avoid driving unless absolutely necessary".
"If necessary, drive with caution and remain vigilant and alert," the government media office said.
Footage shared by Storm Centre, a weather channel run by hobbyists, purported to show icy hail falling on Riyadh City, on the far outskirts of the capital.
In Ras Al Khaimah, authorities said pupils in all government-run schools would switch to remote learning from home until Monday.
Officials said the move was for the safety of parents and pupils.
Thundery showers and some lightning are forecast in the coming days, including overnight on Wednesday into Thursday morning, making flooding on the roads likely.
Friday will also be wet with the eye of the rainstorm passing over the Northern Emirates, a Windy.com chart showed.
Temperatures will dip to 14ºC on the coast and as low as 3ºC in the mountains.
The National Centre of Meteorology said winds could reach 40kph, with rough seas off the coast.
In the Northern Emirates, police urged drivers to steer clear of areas that flood quickly, particularly wadis.
Maj Gen Ali Abdullah bin Alwan Al Nuaimi, chief of Ras Al Khaimah Police, urged motorists to follow basic advice.
“Rainy weather can be very dangerous, especially if drivers are careless, reckless or speeding,” he said.
Seven people died in the Northern Emirates in July when the heaviest rain since 1978 fell in a rare summer storm.
The Emirates, one of the driest countries in the world, uses cloud-seeding technology to enhance rainfall.
Planes disperse salt particles into clouds that can boost precipitation.
The planes are typically sent up on wet days to capitalise on incoming storms, though missions are run throughout the year.
