The 2017–18 Australian region cyclone season was an average period of tropical cyclone formation in the Southern Indian Ocean and South Pacific Ocean, between 90°E and 160°E, with 11 named storms, which 3 intensified into severe tropical cyclones. Another two tropical cyclones, Cempaka (Indonesian region north of 10°S) and Flamboyan (Indonesian and La Réunion's area of responsibility) occurred outside the Australian region but are included in the descriptions below. The season officially began 1 November 2017 and ended on 30 April 2018; however, tropical cyclones can form at any time of the year, as demonstrated by the first tropical low of the season in early August. Any tropical system that forms between 1 July 2017 and 30 June 2018 will count towards the season total. During the season, tropical cyclones will be officially monitored by one of the five tropical cyclone warning centres (TCWCs) that operate in this region. Three of the five centres are operated by the Australian Bureau of Meteorology (BOM) in Perth, Darwin and Brisbane, while the other two are operated by the National Weather Service of Papua New Guinea in Port Moresby and the Indonesian Agency for Meteorology, Climatology and Geophysics in Jakarta. The Joint Typhoon Warning Center (JTWC) of the United States and other national meteorological services, including Météo-France at Réunion, also monitored the basin during the season. __TOC__
Seasonal forecasts Region Averagenumber Chanceof more Chanceof less Actualactivity Whole1156%44%11 Western 752%48%4 North-Western 556%44%4 Northern 353%47%2 Eastern 454%46% 2Source: BOM's Seasonal Outlooks for Tropical Cyclones.
During October, ahead of the tropical cyclone season, the Bureau of Meteorology issued a tropical cyclone outlook for the coming 2017–18 season, which would officially run from 1 November 2017 to 30 April 2018. Seasonal forecasts were issued for the basin as a whole, as well as the Eastern, Northern and Western regions and the North-Western sub-region. The forecasts took into account various factors, including the latest neutral to weak La Niña conditions that had been observed in the tropical Pacific Ocean. The outlooks showed that activity in the basin overall, as well as for each of its individual regions, would be near average. For the Western region between 90°E and 125°E, the BOM forecast that the area would also see activity slightly above its average of 7, with a 52% chance of an above average number of tropical cyclones occurring. TCWC Perth also noted that there was a likelihood of two tropical cyclones and a significant likelihood of at least one severe tropical cyclone impacting Western Australia. For the North-Western sub-region between 105°E and 130°E, it was predicted that activity would be above average, with a 56% chance of above-average tropical cyclone activity. The Northern Territory, which was defined as being between as being 125°E and 142.5°E, had a 53% chance of an above-average season. The Eastern region between 142.5°E and 160°E was predicted to have a slightly above-normal tropical cyclone season, with a 54% chance of above-average tropical cyclone activity.
Seasonal summary
Systems Tropical Low 01U
On 8 August, TCWC Perth started to monitor a tropical low located approximately to the west-northwest of the Cocos Islands, on the 90th meridian east—the western edge of the BOM's area of responsibility. The tropical low moved in a west-southwesterly direction and attained sustained winds south of the circulation center, and a minimum barometric pressure of 1005 hPa (29.68 inHg). The storm moved out of the Australian region on the same day.
Tropical Cyclone Cempaka
On 22 November, TCWC Perth and TCWC Jakarta started to monitor a weak tropical low that had developed about south of the city of Surabaya. By 06:00 UTC of 26 November, TCWC Jakarta began issuing advisories and was classified as a tropical depression. The JTWC, however, issued a Tropical Cyclone Formation Alert early on 27 November, stating that satellite imagery depicted flaring convection near its center. Several hours later, TCWC Jakarta upgraded the system to a tropical cyclone, giving the name Cempaka. Winds from the cyclone also blew ash from nearby Mount Agung on Bali westwards to its popular beaches and far eastern Java. On 30 November, Cempaka weakened into a tropical low, while turning to the southwest. TCWC Perth last mentioned Cempaka on 1 December.
Although Cempaka never made landfall, the rainfall from the storm caused severe flooding and landslides across the southern half of Java and Bali, killing at least 41 people and destroying many homes and businesses.
Tropical Low 04U
On 24 November, TCWC Darwin started to monitor a weak tropical low that had developed in the Banda Sea. The system moved in a slow direction, and attained a minimum pressure of 1005 hPa, until it was last mentioned on 29 November.
Tropical Cyclone Dahlia
Tropical Low 03U was first noted as a tropical depression by TCWC Jakarta on 24 November, while it was located about to the west of Jakarta, Indonesia. By 29 November, TCWC Jakarta upgraded the system to a tropical cyclone, receiving the name Dahlia, making it the first time where at least two cyclones were formed and named by TCWC Jakarta in a single season. The JTWC followed suit the next day, designating the system as 01S. Best track reanalysis by the Bureau of Meteorology concluded that Dahlia reached tropical cyclone intensity as a Category 2, with sustained winds of 50 knots on 1 December and a minimum barometric pressure of 985 hPa. Dahlia maintained its intensity for several hours until the storm moved southeastwards and began to rapidly weaken on 2 December as it interacted with Ex-Tropical Cyclone Cempaka. Dahlia briefly reintensified for a period on 3 December. The BoM later issued its final bulletin on Dahlia early on 4 December. TCWC Perth last monitored on Dahlia on 5 December.
Tropical Cyclone Hilda
During 26 December, the BoM reported that a tropical low had developed just off the Kimberley coast, about to the north of Derby. The system subsequently moved south-southwest parallel to the coast, as it developed further before it moved overland to the southwest of Cape Leveque. The system was subsequently classified as a Category 1 tropical cyclone on 27 December and named Hilda by the BoM, while it was located inland near Broome based on reports of persistent gale-force winds from Broome Airport. Soon back over water, the system strengthened more, and was classified as a Category 2 tropical cyclone with 10-minute peak windspeeds of . Late that same day, Hilda made a second and final landfall just north of Bidyadanga at near peak intensity. Inland, the cyclone moved south-southeastward, weakening into a tropical low by the afternoon of 28 December, and then dissipating the following day. Overall, Hilda caused only minor damage as it moved through western Kimberley.
Tropical Cyclone Irving
On 3 January, a tropical low had developed to the southwest of Sumatra. On 06:00 UTC of 5 January, TCWC Perth began issuing advisories on the system, using the identifier 08U. TCWC Perth had recorded winds of , despite the fact that the system did not have the structure of a tropical cyclone. By the next day, 08U then strengthened into a Category 1 tropical cyclone, with the storm receiving the name Irving, the fourth named storm of the season. Three hours later, the JTWC followed suit and gave the system the designation 04S. TCWC Perth, however, discontinued advisories after Irving exited the basin on 12:00 UTC the same day.
Tropical Cyclone Joyce
A tropical low developed over the Joseph Bonaparte Gulf on 7 January 2018, and moved over the Kimberley region of Western Australia the next day. On 10 January, the low moved offshore and began to develop, and the system was upgraded to a tropical cyclone, named Joyce, on 11 January. The system made landfall on the Western Australian coast the following day. The remnants of Cyclone Joyce bought heavy rain to the Perth Metro Area on 15 January; a total of of rain in 24 hours fell in Perth, while Rottnest Island recorded the highest amount of rain in the metro, which was a total of .
Flood Watches and Warnings were issued for the De Grey, Gascoyne, Greenough, Moore Hill, Ord River catchments and the Sandy Desert and West Kimberley river districts with minor flooding recorded in the De Grey and Gascoyne River catchments.
Tropical Low 11U
The slow-moving system brought copious rains to a broad swath of coastal Australia. In Kimberley, Western Australia, near-record rainfall accumulations of in four days caused extensive flooding. In a 24-hour span, of rain fell across Broome, Western Australia, with flood waters in some areas reaching depths of . Portions of the Great Northern Highway and Cape Leveque road were closed. Coastal areas experienced powerful winds reaching with gusts to ; these winds downed many trees and power lines. The effects of the low were considered substantially worse than Hilda and Joyce, tropical cyclones that affected the same region earlier in the season.
Severe Tropical Cyclone Kelvin
Tropical Cyclone Kelvin formed on 12 February and rapidly intensified into a Category 2 Storm (Australian Scale) and a Category 1 Storm (Saffir–Simpson) Kelvin made landfall, but unusually formed an eye over land. Kelvin sustained cyclone or hurricane intensity until dissipating on 20 February. Tropical Cyclone Kelvin brought widespread heavy rainfall to the Kimberley region which had already been saturated by other tropical cyclone systems. As a result, significant flooding occurred in parts of the Kimberley, including in the towns of Broome and Bidyadanga. Property damage was sustained at Broome and Anna Plains Station, where the cyclone made landfall, as well as infrastructural damage to the Great Northern Highway as a result of the heavy rainfall and flooding.
Tropical Cyclone Linda
On 11 March, the Fiji Meteorological Service reported that Tropical Disturbance 10F had developed about to the southwest of Rennell and Bellona Province of the Solomon Islands. The system was poorly organised, with atmospheric convection displaced to the east of the low-level circulation centre. On the morning of 12 March, following some mild strengthening, the JTWC upgraded the disturbance to a tropical depression, and the Bureau of Meteorology assigned the system the tropical low designation 21U. Late the same day, the JTWC assessed the system to be producing gale-force winds, and upgraded it to tropical storm status on the Saffir–Simpson scale. The storm moved generally southwards and entered the Australian region at 10:00 AEST on 13 March. Despite being exposed to generally unfavourable atmospheric conditions for tropical cyclone development, the tropical low strengthened into a category 1 tropical cyclone on the Australian scale six hours later. The storm was named "Linda", and was the first tropical cyclone in the Eastern Region for the 2017–18 season. Tropical Cyclone Linda attained its peak intensity at 22:00 AEST 13 March, with 10-minute sustained winds, one-minute sustained winds, and a minimum atmospheric pressure of .
A few hours later, the storm assumed a more southwesterly course towards the southern Queensland coast. As a result of the further deteriorating atmospheric conditions and cooling sea surface temperatures due to movement away from warm equatorial waters, Linda weakened to a subtropical low during mid-morning on 14 March, having spent fewer than 24 hours as a cyclone. The JTWC proceeded to downgrade the system below tropical storm intensity at 04:00 AEST on 25 March. The remnant low transitioned to a south-southeasterly track and continued to decay while travelling roughly parallel to the coastline, finally dissipating on 16 March.