The 2019–20 Australian region cyclone season was a below average tropical cyclone season for the waters surrounding Australia between longitudes 90°E and 160°E. The season officially began on 1 November 2019 and ended on 30 April 2020; however, tropical cyclones can form at any time of year, as evidenced by Tropical Cyclone Mangga during May 2020. As such, any system existing between 1 July 2019 and 30 June 2020 would count towards the season total. The season featured the region's second-latest start on record (behind only the 2002–03 season), with the formation of the first tropical low only occurring on 4 January 2020. A total of eight tropical cyclones formed during the season, which represents the region's least active season since the 2016–17 season. Three systems intensified further into severe tropical cyclones, and three systems made landfall within the region at tropical cyclone intensity. A total of 28 fatalities were caused, either directly or indirectly, as a result of impacts from the season's systems. Cyclone Ferdinand was the strongest of the season reaching Category 4 in late February 2020. However, it was the second-strongest storm, Cyclone Damien, that was the most damaging. Damien was the strongest tropical cyclone to strike Western Australia's Pilbara Region since Cyclone Christine in 2013, making landfall directly over the town of Dampier.
During the season, tropical cyclones were officially monitored by the Australian Bureau of Meteorology (BOM), the Meteorology, Climatology, and Geophysical Agency (BMKG), and the National Weather Service of Papua New Guinea. The United States' Joint Typhoon Warning Center (JTWC) and other national agencies such as the Fiji Meteorological Service (FMS), the Meteorological Service of New Zealand (MetService), and Météo-France at La Réunion also monitored parts of the basin during the season.
Seasonal forecasts
Ahead of the cyclone season formally starting on 1 November, the BoM, Fiji Meteorological Service (FMS), New Zealand's MetService and National Institute of Water and Atmospheric Research (NIWA) and various other Pacific Meteorological services, all contributed towards the Island Climate Update tropical cyclone outlook that was released during October 2019. The outlook called for a near-average number of tropical cyclones for the 2019–20 season, with nine to twelve named tropical cyclones, predicted to occur between 135°E and 120°W, compared to an average of just over 10. At least four of the tropical cyclones were expected to intensify further and become severe tropical cyclones, while it was noted that a Category 5 severe tropical cyclone could occur during the season.
In addition to contributing towards the Island Climate Update outlook, the BoM issued seven seasonal forecasts for various parts of the Australian region and South Pacific basin. For the entire Australian region between 90°E–160°E, the BoM predicted that the season would feature, a below-average amount of systems with only a 35% chance of more tropical cyclones. The BoM also thought that their self defined Western and Eastern regions, would both have a 57% chance of fewer tropical cyclones than normal developing. Their northern region and northwestern subregion would also see fewer tropical cyclones than normal, with only a 36% and 39% chance of more tropical cyclones than average. The BoM also issued two seasonal forecasts for their self-defined eastern and western regions of the South Pacific Ocean. They predicted that the Western region between 142.5°E and 165°E, had a 54% chance of seeing activity above its average of 4 tropical cyclones. The BoM also predicted that the Eastern Region between 165°E and 120°W, had a 41% chance of seeing activity above its average of 7 tropical cyclones.
The outlooks accounted for the effects of various major Australian climate drivers, namely the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). The BOM noted that sea surface temperature anomalies across the equatorial Pacific Ocean had been characteristic of a neutral ENSO phase since April. The international climate models utilised by the BOM also indicated that the neutral conditions would likely persist until at least February. A neutral ENSO phase typically has little influence on the Australian climate. Warmer than average sea surface temperatures in the central and western tropical Indian Ocean and cooler waters near Indonesia and northern Australia, indicating a positive IOD phase, had also persisted since May. The temperature difference increased throughout the year, and at the beginning of October, the BOM noted that the sea surface temperature anomaly of +1.76 °C was the highest observed value on record (since 2001). The anomaly continued to increase rapidly after this, with the value reaching +2.15 °C a fortnight (two weeks or fourteen days) later. The record-strength positive IOD contributed to the development of a region of higher than normal atmospheric pressure across northern Australia during September, after having remained near neutral throughout winter. The BOM noted that these factors also contributed to the tropical cyclone season outlook.
Season summary
The season had an unusually late start with the first system, Blake, forming in early January, well after the official start of the season. Blake would later make landfall in northwestern Australia and soon degenerate afterwards. At the same time, Claudia, another tropical cyclone, formed. It persisted for two weeks and reached category 3 on the Australian tropical cyclone scale before dissipating west of Australia. Later that month, a tropical low formed and lasted for a week before dissipating in late January without been named. Three other tropical lows formed in late January and early February. One of them dissipated later. Another one of them has been moving in and out of the Australian region. It was designated 06F by the Fiji Meteorological Service. The third one intensified into Cyclone Damien. In late February, 2 new tropical lows formed, and were named Esther and Ferdinand. Esther didn't strengthen much, but Ferdinand went on to become a Category 3 severe tropical cyclone, equivalent to a Category 2 Atlantic Hurricane. Then in the month of March and April, two cyclones namely Gretel and Harold formed in the Coral Sea and both of them exited the basin towards the South Pacific Ocean where it intensified further. The season continued into May where two lows formed in the region of TCWC Jakarta where the latter one was named as Mangga which became the strongest Extratropical cyclone to hit Western Australia such late in the season. The season concluded on 23 May with the Extratropical transition of Cyclone Mangga.
Systems
Tropical Cyclone Blake
During 4 January, the BOM reported that Tropical Low 02U had started to develop within a monsoon trough, about 750 km (470 mi) north-northwest of Broome. Citing considerable rotation extending into the mid troposphere, well-established dual-channel outflow and warm sea surface temperatures, the JTWC assessed the system as having a moderate chance of attaining tropical cyclone intensity within the following 24 hours. The system gradually gathered strength in the favourable environment as it tracked slowly towards the south-southwest, leading the JTWC to issue a Tropical Cyclone Formation Alert at 03:30 UTC the following day. The BOM indicated that sustained gale-force winds had developed on the western side of the tropical low at 15:00 UTC, and the system was designated as Tropical Cyclone 06S by the JTWC a few hours later. Gales fully encircled the system by 00:00 UTC on 6 January, prompting the BOM to upgrade the low to a Category 1 tropical cyclone on the Australian scale, the first of the season. The system was given the official name Blake by the BOM.
Blake began to intensify steadily after being upgraded into a tropical cyclone, attaining 10-minute sustained winds of 75 km/h (45 mph) and one-minute sustained winds of 105 km/h (65 mph) within a few hours. Soon afterwards, however, the system's development stalled due to land interaction with the nearby coastline of Western Australia. The cyclone made landfall on Dampier Peninsula just before 09:00 UTC, approximately 85 km (53 mi) north of Broome. Blake turned to the southwest and re-emerged over the Indian Ocean at 15:00 UTC; however, the system's structure had deteriorated significantly while the centre was over land. As the weakened cyclone continued over water towards the southwest, paralleling the coastline, low vertical wind shear allowed an area of deep convection to gradually redevelop over the system on 7 January. Blake made its final landfall just to the west of the Wallal Downs cattle station on Eighty Mile Beach at approximately 17:00 UTC at minimal Category 1 intensity. Within an hour of crossing the coast, the system weakened to a tropical low. The JTWC discontinued advisories at 00:00 UTC on 8 January as the system moved farther inland; however, the system maintained tropical storm intensity until 12 hours later.
Severe Tropical Cyclone Claudia
On 4 January, the BOM noted the formation of a weak tropical low over Indonesia's Maluku Islands. In the ensuing days, the tropical low tracked slowly southeastwards across the Arafura Sea, towards the Gulf of Carpentaria. Significant development was hampered by strong vertical wind shear; however, very warm sea surface temperatures of up to 32 °C (90 °F) allowed the low to gradually increase in organisation. On 7 January, shortly after the low passed near Cape Wessel in the Northern Territory, the BOM published their first forecast track map for the system, and issued a tropical cyclone watch for the northern coastline of Arnhem Land. On the next day, the JTWC issued a Tropical Cyclone Formation Alert on the system as it began to organize just northwest of the Gove Peninsula. As the system remained disorganized, the JTWC cancelled the first Tropical Cyclone Formation Alert, but later issued another one on 10 January as it re-organized itself, following land interaction with the Top End. It was later upgraded to a tropical cyclone by the BOM as it was northeast of Kalumburu, receiving the name Claudia on 11 January. On the next day, the system was upgraded to a category 2 tropical cyclone. Several hours later, following a decrease in wind shear, Claudia's structure quickly improved, with the storm acquiring hurricane-force winds. It was then upgraded by the BOM to a severe tropical cyclone, during this intensification spell.
The storm continued intensifying, indicated by an improvement of the storm's structure over the proceeding hours. The storm eventually reached its peak intensity with 1-minute sustained winds of 90 mph (145 km/h) and 969 millibars with a small, ragged eye forming on microwave imagery on 13 January. Despite this, a decrease in sea surface temperatures as it quickly accelerated eastwards caused the storm to rapidly weaken throughout 14 January, indicated by a loss of deep convection near the storm's center. The next evening on 15 January, the BOM issued their last advisory on Claudia as it began to weaken. Claudia dissipated as a tropical low on 17 January.
When the system was still a tropical low on 10 January, portions of the Top End received unusually large amounts of rainfall due to the system's slow movement. Darwin received 45 mm (1.8 in) of rain, Noonamah received 56 mm (2.2 in) of rain, Pirlangimpi received 80.8 mm (3.18 in) of rain, Charles Point received 151 mm (5.9 in) of rain, and Dum In Mirrie Island received a staggering 410 mm (16 in) of rain as a result of the system.
Tropical Low 04U
On 24 January, the BOM noted that a weak tropical low had formed inland over the northeastern Northern Territory, near Cresswell Downs. Embedded in a low-pressure trough stretching across northern Australia and into the South Pacific Ocean, the tropical low remained slow-moving over the ensuing days. After meandering just south of the Gulf of Carpentaria, the system moved offshore at about 12:00 UTC on 27 January, just to the southeast of Mornington Island. This allowed atmospheric convection to develop, and the central atmospheric pressure deepened to 998 hPa (29.47 inHg) at 18:00 UTC. The system's period over water proved short-lived, however, and the tropical low moved into the Gulf Country of northern Queensland a few hours later. On 29 January, the tropical low began to track rapidly southwestwards towards central Australia, causing the system's convection to degrade due to interaction with the dry Australian outback. The tropical low dissipated near Alice Springs in the southern Northern Territory the following day.
Persisting thunderstorms associated with the low brought long-lived heavy rainfall throughout much of Gulf Country in northern Queensland, due to the storm's abnormally slow movement. The city of Townsville received over 320 mm (13 in) of rain, breaking the previous daily rainfall record in the city of 190 mm (7.5 in). An apartment building was reported to have "severely flooded" near the same town. A peak 475 mm (18.7 in) rainfall total was recorded at the Ayr DPI Research Station in northern Queensland, as a result of the low.