Cyclone Ilsa
Severe Tropical Cyclone Ilsa was a powerful tropical cyclone that struck Australia's Western Australia in April 2023. The sixth named storm, and the fifth severe tropical cyclone of the 2022–23 Australian region cyclone season, Ilsa formed from a tropical low off the coast of Indonesia on 6 April. It fluctuated in intensity and became a Category 1 tropical cyclone on 11 April, after deep convection became symmetric around the low-level circulation center. Ilsa then rapidly intensified the following day and reached its peak intensity as a Category 5 severe tropical cyclone on the Australian tropical cyclone intensity scale. Ten-minute sustained winds were estimated as 230 km/h (145 mph), with a central barometric pressure of 915 hPa (27.02 inHg).[1] One-minute sustained winds reached 260 km/h (160 mph) at this time, equivalent to a Category 5 hurricane on the Saffir–Simpson hurricane wind scale. 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. Ilsa made landfall roughly 120 km (75 mi) northeast of Port Hedland, Western Australia. Inland, Ilsa weakened to a low-end tropical cyclone with 85 km/h (50 mph) winds. Overall, Ilsa caused around A$4 million in damage, and caused 8 deaths after two boats capsized off the coast of Western Australia.
![]() Ilsa near peak intensity while approaching Western Australia on 13 April | |
Meteorological history | |
---|---|
Formed | 6 April 2023 |
Dissipated | 15 April 2023 |
Category 5 severe tropical cyclone | |
10-minute sustained (Aus) | |
Highest winds | 230 km/h (145 mph) |
Lowest pressure | 915 hPa (mbar); 27.02 inHg |
Category 5-equivalent tropical cyclone | |
1-minute sustained (SSHWS/JTWC) | |
Highest winds | 260 km/h (160 mph) |
Lowest pressure | 919 hPa (mbar); 27.14 inHg |
Overall effects | |
Fatalities | 8 |
Damage | A$4 million |
Areas affected | Maluku, Lesser Sunda Islands, Northern Territory, Western Australia |
Part of the 2022–23 Australian region cyclone season |
Meteorological history

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

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]

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]
Preparations and impact

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]
Retirement
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]
See also
- 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.
Notes
- The position of Ilsa's Category 5 peak is not depicted in this graphic as it is an asynoptic point (i.e. not at the 6-hour intervals of all other points) occurring at 09:00 UTC 13 April.
References
- "Australian Tropical Cyclone Database" (CSV). Australian Bureau of Meteorology. 30 June 2023. Retrieved 30 June 2023. A guide on how to read the database is available here.
- Tropical Cyclone Report: Severe Tropical Cyclone Ilsa (Report). Australian Bureau of Meteorology. Retrieved 6 May 2023.
- Significant Tropical Weather Advisory for the Indian Ocean, 02Z 6 April 2022 (Report). United States Joint Typhoon Warning Center. 6 April 2022. Archived from the original on 21 December 2017. Retrieved 6 April 2022. Alt URL
- Tropical Cyclone Formation Alert (Invest 98S) (Report). United States Joint Typhoon Warning Center. 7 April 2023. Archived from the original on 7 April 2023. Retrieved 7 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Eighteen) Warning No. 1 (Report). United States Joint Typhoon Warning Center. 8 April 2023. Archived from the original on 8 April 2023. Retrieved 8 April 2023. Alt URL
- Prognostic Reasoning for Tropical Disturbance 18S (Eighteen) Warning No. 3 (Report). United States Joint Typhoon Warning Center. 9 April 2023. Archived from the original on 9 April 2023. Retrieved 9 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Eighteen) Warning No. 9 (Report). United States Joint Typhoon Warning Center. 9 April 2023. Archived from the original on 9 April 2023. Retrieved 9 April 2023. Alt URL
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 11 April 2023. Archived from the original on 11 April 2023. Retrieved 11 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Eighteen) Warning No. 11 (Report). United States Joint Typhoon Warning Center. 11 April 2023. Archived from the original on 11 April 2023. Retrieved 11 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Ilsa) Warning No. 11 (Report). United States Joint Typhoon Warning Center. 11 April 2023. Archived from the original on 11 April 2023. Retrieved 11 April 2023. Alt URL
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 11 April 2023. Archived from the original on 12 April 2023. Retrieved 12 April 2023.
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 12 April 2023. Archived from the original on 12 April 2023. Retrieved 12 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Ilsa) Warning No. 15 (Report). United States Joint Typhoon Warning Center. 12 April 2023. Archived from the original on 12 April 2023. Retrieved 12 April 2023. Alt URL
- Prognostic Reasoning for Tropical Cyclone 18S (Ilsa) Warning No. 17 (Report). United States Joint Typhoon Warning Center. 12 April 2023. Archived from the original on 12 April 2023. Retrieved 12 April 2023. Alt URL
- Tropical Cyclone Forecast Track Map for Severe Tropical Cyclone Ilsa (Report). Australian Bureau of Meteorology. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- Prognostic Reasoning for Tropical Cyclone 18S (Ilsa) Warning No. 18 (Report). United States Joint Typhoon Warning Center. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- "JTWC Best Track on Tropical Cyclone Ilsa (18S)". National Oceanic and Atmospheric Administration. Archived from the original on 14 April 2023. Retrieved 14 April 2023.
- "Severe Tropical Cyclone Ilsa to cross WA coast as powerful category five system". ABC News. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- Bureau of Meteorology, Western Australia [@BOM_WA] (13 April 2023). "#CycloneIlsa has set a new preliminary Australian ten-minute sustained wind speed record of 218km/h at Bedout Island! Cyclone George was the previous record holder with 194km/h back in 2007 at the very same location!" (Tweet). Archived from the original on 13 April 2023 – via Twitter.
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- Tropical Cyclone 18S (Ilsa) Warning No. 21 (Report). United States Joint Typhoon Warning Center. 13 April 2023. Archived from the original on 14 April 2023. Retrieved 13 April 2023.
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 13 April 2023. Archived from the original on 14 April 2023. Retrieved 13 April 2023.
- "Tropical Cyclone Technical Bulletin (Western Region)". Australian Bureau of Meteorology. 14 April 2023. Archived from the original on 15 April 2023. Retrieved 15 April 2023.
- "Tropical cyclone 'Ilsa' could hit parts of WA coast". WAtoday. 9 April 2023. Archived from the original on 9 April 2023. Retrieved 9 April 2023.
- "Cyclone Ilsa: Residents flee as intensifying cyclone approaches northwest Australia". Alarabiya News. 12 April 2023. Archived from the original on 12 April 2023. Retrieved 12 April 2023.
- "Australia's most powerful cyclone in 8 years to cross coast". ABC News. Archived from the original on 14 April 2023. Retrieved 14 April 2023.
- Jarred, Cross (12 April 2023). "Pilbara and Kimberely prepare to shelter as Cyclone Ilsa reaches category 3, continues towards coast". Retrieved 13 April 2023.
- "Western Australia battens down as Cyclone Ilsa gathers strength". 1 News. Archived from the original on 12 April 2023. Retrieved 13 April 2023.
- Anderson, Anthony (13 April 2023). "Tropical Cyclone Ilsa intensifies further to category 4 system". Retrieved 13 April 2023.
- "Cyclone Ilsa: Western Australia braces for category 4 storm". BBC News. 13 April 2023. Archived from the original on 13 April 2023. Retrieved 13 April 2023.
- "Australia's northwest braces for strongest cyclone in a decade". www.aljazeera.com. Retrieved 13 April 2023.
- "Western Australia assesses Cyclone Ilsa's 'path of destruction'". Reuters. 15 April 2023. Archived from the original on 15 April 2023. Retrieved 15 April 2023.
- "Engineers to assess how to cyclone-proof outback buildings as Ilsa clean-up gets underway". ABC News. 14 April 2023. Archived from the original on 14 April 2023. Retrieved 15 April 2023.
- "Roadhouse at centre of Cyclone Ilsa estimates damage at more than $4 million". The Age. Archived from the original on 14 April 2023. Retrieved 13 April 2023.
- "Cyclone Ilsa leaves million-dollar damage bill after record winds but storm threat 'not over yet'". www.9news.com.au. Archived from the original on 14 April 2023. Retrieved 15 April 2023.
- "Powerful Cyclone Ilsa lashes Australia's northwest coast". WTOP News. 14 April 2023. Archived from the original on 15 April 2023. Retrieved 15 April 2023.
- Murphy, Hannah; Barker, Anne; Brann, Matt; Bieundurry, Tallulah (3 May 2023). "Indonesian fishermen who survived cyclone that killed eight off WA coast won't face charges". ABC News. Retrieved 10 May 2023.
- http://www.bom.gov.au/cyclone/tropical-cyclone-knowledge-centre/understanding/tc-names/
External links

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