However, on 18 September 2019, the haze returned to Singapore, resulting in the PSI increasing to "unhealthy" levels seen last weekend.[35] This caused Firefly to cancel all flights from Seletar Airport for the next two days.[36][37] The next day, the PSI peaked at 154 around 4am in southern Singapore before improving progressively[38], with all parts of Singapore registering a "moderate" level by 9pm.[39]