Inter-monsoon conditions which have been prevailing since late March are forecast to continue into this month, the weatherman said.
More occurrences of thundery showers can be expected over Singapore and the surrounding region, and low-level winds are forecast to be light and variable in direction.
In its latest regular weather advisory, the National Environment Agency (NEA) noted that May has one of the highest number of lightning days in the year. It is also one of the warmest months.
Strong solar heating of land areas during the day is expected to bring short moderate to heavy thundery showers in the afternoon on four to six days in the first half of this month, and the showers could extend into the evening on a few of these days.
On some days, particularly in the second week, Sumatra squalls could bring widespread thundery showers with gusty winds before dawn and in the morning, the NEA added.
A Sumatra squall is an organised line of thunderstorms that typically develops over Sumatra island or the Strait of Malacca.
Warm conditions will persist, with the daily temperature forecast to range between 25 deg C and 34 deg C on most days.
The heat can be sweltering on a few days, as the daily maximum temperature could reach around the high end of the 35 deg C range when there is little or no rainfall.
Last month saw inter-monsoon conditions with low-level winds prevailing over Singapore. Throughout the month, thundery showers fell over the island in the afternoon on most days, and extended into the evening on a few of these days.
This was due to strong solar heating of land areas and light winds over Singapore and the surrounding vicinity.
Last Friday, the Sumatra squall over Singapore between the late morning and afternoon recorded a daily total rainfall of 118.7mm in Changi, the highest rainfall recorded in a day in April this year.
But last month was also particularly warm, with daily maximum temperature exceeding 34 deg C on more than half the days.
Last month's highest daily maximum temperature of 36.4 deg C was recorded in Paya Lebar on April 17, close to the highest ever recorded daily maximum temperature of 37 deg C - in 1983 - for April since temperature records started in 1929.
More than two-thirds of Singapore received slightly below-normal rainfall last month.
Rainfall was lowest in Seletar where 143.2mm (36 per cent below average) of rain was recorded. The highest rainfall of 299.8mm (53 per cent above average) was recorded in Tanjong Katong.