Additionally, record-breaking ten-minute sustained wind speed of 219 km/h (136 mph) were measured at Bedout Island, beating the previous record of Cyclone George in 2007.

An active burst of the Madden–Julian oscillation in conjunction with a westward-propagating equatorial Rossby wave led to the formation of a tropical low on 6 April.

[1] By the next day, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert on the system, citing the slightly favourable environmental conditions encompassing poleward outflow and warm sea surface temperatures (SST) of 29–30 °C (84–86 °F) subduing high vertical wind shear.

[3] More consolidation took place, with spiral rainbands present in all quadrants of the storm wrapping around the LLCC obscured by a cold dense overcast (CDO).

[8] On the same day, Ilsa rapidly intensified into a Category 3 severe tropical cyclone within a favourable environment of low shear and warm SST.

[9] Ilsa then underwent steady intensification under persistent wind shear, as SST and ocean heat content increased along the way, with cloud top temperatures of at least −92 °C (−134 °F).

[12] Later the next day, the BoM assessed the storm to have attained ten-minute sustained winds of 165 km/h (105 mph), ranking it as a Category 4 severe tropical cyclone.

[13] Owing to the substantial radial outflow and very warm SST, despite moderate wind shear, Ilsa intensified into a Category 4-equivalent tropical cyclone on the SSHWS.

[16] Later that same day, Ilsa had become a Category 5 severe tropical cyclone with sustained winds of 230 km/h (145 mph) and the lowest atmospheric pressure of 915 hPa (27.02 inHg).

[17] Following this, the JTWC discontinued the issuing of advisories of Ilsa, as the storm accelerated inland and rapidly deteriorated from land interaction and high vertical wind shear.

[25] On 12 April, the Department of Fire and Emergency Services (DFES) issued a cyclone yellow alert, and urged residents to be prudent and to take action and prepare to shelter.

[28] Western Australia's Emergency Department on 15 April assessed damage from Ilsa,[29] with at least eight personnel were sent to the Great Northern Highway fires near Pippingarra.