Cyclone Ilsa

Map plotting the storm's track and intensity, according to the Saffir–Simpson scale[nb 1]

Map key

Saffir–Simpson scale

  Tropical depression (≤38 mph, ≤62 km/h)
  Tropical storm (39–73 mph, 63–118 km/h)
  Category 1 (74–95 mph, 119–153 km/h)
  Category 2 (96–110 mph, 154–177 km/h)
  Category 3 (111–129 mph, 178–208 km/h)
  Category 4 (130–156 mph, 209–251 km/h)
  Category 5 (≥157 mph, ≥252 km/h)
  Unknown

Storm type

Tropical cyclone

Subtropical cyclone

Extratropical cyclone, remnant low, tropical disturbance, or monsoon depression

On 6 April, an active burst of the monsoon trough led to the development of a tropical low in the Timor Sea.[2] Deep convection persisted in the system's southern semicircles.[3] By the next day, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert (TCFA) on the system.[4] During the following day, the JTWC initiated advisories on the system and classified it as Tropical Cyclone 18S.[5]

Cyclone Ilsa continuing to intensify off the coast of Western Australia on 12 April

Easterly vertical wind shear decreased as a result of the intense convective mass causing upper-level winds around it.[6] Over the next subsequent days, the low steadily drifted to the southwest, but due to unfavorable environmental conditions, intensification was delayed.[2][7] Late on the next day, the BoM reported that the tropical low had developed into a Category 1 tropical cyclone and named it Ilsa.[8] By that time, it had developed an obscured low-level circulation center.[9] Satellite imagery showed that a CDO was obscuring the LLCC, and Ilsa intensified further into a Category 1-equivalent cyclone.[10] A burst of convection occurred near Ilsa's center during six hours later, and the BoM reported that it briefly strengthened into a Category 2 cyclone.[11] Ilsa rapidly intensified, into a Category 3 severe tropical cyclone, within a favorable environment with low shear and warm sea surface temperature (SST).[12] Ilsa shows an eye feature seen in microwave imaging, with IIsa later becoming a Category 2-equivalent cyclone.[13] The eye in the symmetric system later became visible on satellite imagery as the rainbands wrapped around the center tightened after intensifying to a Category 3-equivalent tropical cyclone.[14]

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.[15] On 13 April, the JTWC also assessed Ilsa to have attained an intensity equivalent to a Category 4-equivalent tropical cyclone on the Saffir–Simpson hurricane scale.[16] Later that day, Ilsa strengthened further to its peak intensity as a Category 5-equivalent tropical cyclone with 1-minute sustained winds of 260 km/h (160 mph).[17] An automated weather station on Rowley Shoals recorded wind gusts up to 235 km/h (146 mph).[18] Later that same day, Ilsa had become a Category 5 severe tropical cyclone with sustained winds of 205 km/h (125 mph).[19]

A record-breaking ten-minute sustained wind speed of 219 km/h (136 mph) was measured at Bedout Island, beating the previous record of Cyclone George in 2007.[20] The cyclone crossed the coast about 120 km (75 mi) northeast of Port Hedland on 16:00 UTC, with sustained winds of 215 km/h (130 mph).[21] Shortly after the landfall, the JTWC discontinued warnings on the system.[22] While over Western Australia, Ilsa weakened to a Category 4 severe tropical cyclone with 175 km/h (110 mph) winds.[23] The storm continued to weaken with a deteriorating cloud signature.[24] Ilsa was last noted on 15 April.[2]

Cyclone Ilsa making landfall east of Port Hedland, WA on 13 April.

Gale-force winds with gusts up to 165 km/h (105 mph), and heavy rain might occur on 9 April between Kalumburu and Kuri Bay in the state's north.[25] Squally thunderstorms are also anticipated in far northern Kimberley.[25] Residents across the coast of Pilbara evacuated as high tides, large waves and inundation were possible, along with a highway closure along the Pilbara coast.[26][27] In anticipation of Ilsa, the BoM issued a warning for Western Australia’s Kimberley and Pilbara regions.[28]

Additional emergency workers, aircraft and essential supplies have also been sent to the region.[29] 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.[30] At least 700 residents were being evacuated to cyclone shelters prior to the storm.[31] Port Hedland mayor Peter Carter said damaging winds could turn flying debris into "missiles in the air".[32]

Western Australia's Emergency Department on 15 April assessed damage from a tropical cyclone that hit the northwest of the state.[33] At least eight personnel have been sent to the Great Northern Highway fires near Pippingarra.[34] Pardoo Roadhouse, located northeast of Port Hedland and near the landfall point, sustained major damage valued at A$4 million.[35] Five accommodation sheds were entirely blown away by the storm at the Pardoo Roadhouse, and emergency officials have been unable to locate them.[36] Apart from Pardoo, acting emergency services minister Sue Ellery called the storm damage "fairly minimal."[37]

Two boats containing 19 men total illegally fishing off the coast of Western Australia were caught in the cyclone. One of the boats was found shipwrecked on Bedwell Island, while the other boat sank. The 11 people on the shipwrecked boat were rescued, while one survivor was found from the sunken boat. The other 8 fishermen died.[38]

As a result of the damage associated with the storm, the name Isla was removed from the list of Australian region cyclone names and will never be used again for a tropical cyclone in that basin. It was replaced by Isabella for future seasons.[39]

• Tropical cyclones in 2023
• Weather of 2023
• Cyclone Ilona (1988)
• Cyclone Orson (1989) – a powerful tropical cyclone that had a similar path and intensity.
• Cyclone John (1999)
• Cyclone George (2007)
• Cyclone Laurence (2009)
• Cyclones Heidi and Lua (2012) – two severe tropical cyclones which both made landfall around Pardoo within the span of two months.
• Cyclone Kelvin (2018) – the previous severe tropical cyclone to make landfall between Broome and Port Hedland prior to Ilsa.

Wikimedia Commons has media related to Cyclone Ilsa (2023).

• Australian Bureau of Meteorology
• Joint Typhoon Warning Center
• Tropical Cyclone Warning Center Jakarta (in Indonesian)
• Papua New Guinea National Weather Service