page_title: Cyclone Nora
section_title: Meteorological history
hierarchical_section_title: Cyclone Nora / Meteorological history
caption_attribution_description: English: Track map of Severe Tropical Cyclone Nora of the 2017-18 Australian region cyclone season. The points show the location of the storm at 6-hour intervals. The colour represents the storm's maximum sustained wind speeds as classified in the Saffir–Simpson scale (see below), and the shape of the data points represent the nature of the storm, according to the legend below. Saffir–Simpson scale Tropical depression≤38 mph≤62 km/h Category 3111–129 mph178–208 km/h Tropical storm39–73 mph63–118 km/h Category 4130–156 mph209–251 km/h Category 174–95 mph119–153 km/h Category 5≥157 mph≥252 km/h Category 296–110 mph154–177 km/h Unknown Storm type Tropical cyclone Subtropical cyclone Extratropical cyclone / Remnant low / Tropical disturbance / Monsoon depression
context_page_description: Severe Tropical Cyclone Nora was a strong tropical cyclone that affected Far North Queensland and the northeastern Northern Territory during March 2018. The ninth named storm and third severe tropical cyclone of the 2017–18 Australian region cyclone season, Nora developed from a tropical low which formed near the Torres Strait on 19 March. The system initially moved quickly to the west-northwest, and then began tracking slowly southwestwards over the Arafura Sea while gradually developing. A turn to the east on 22 March brought the tropical low into a favourable environment for strengthening, and the system reached tropical cyclone intensity later that day. Nora then underwent a period of rapid intensification as it moved southeastwards into the Gulf of Carpentaria. The storm peaked on 23 March as a high-end Category 3 severe tropical cyclone with sustained winds of 155 km/h and a minimum barometric pressure of 958 hPa. Nora made landfall north of Pormpuraaw at about 13:00 UTC on 24 March as a minimal Category 3 system. Nora weakened steadily as it tracked southwards along the coast, and was downgraded to a tropical low the following day.
context_section_description: Several atmospheric features and climate drivers which are typically conducive to tropical cyclogenesis were present in Australian longitudes during March 2018. In early- to mid-March, a monsoon trough developed to the north of Australia, stretching from the eastern Indonesian archipelago to the northern Coral Sea. Although associated convective activity decreased somewhat as the monsoon trough began to weaken, this was offset by the interaction of significant cross-equatorial flow from the Northern Hemisphere with a large area of strong southeasterly wind from the Australian continent. The convergence of these winds provided ample rotational energy for the development of any low-pressure systems in the region. Reinforced by the effects of a westwards-propagating Rossby wave, the southeasterly wind flow contributed to enhanced atmospheric circulation over the tropical waters. In addition, the presence of a weak but discernible pulse of the Madden-Julian Oscillation in the Maritime Continent supported the generation of cloudy weather and increased atmospheric instability in the region.  
  Monsoonal activity began to restrengthen later in the month, and on 19 March the Australian Bureau of Meteorology (BOM) noted that a tropical low had developed in the vicinity of the Torres Strait, embedded within the monsoon trough. The newly formed tropical low moved quickly to the west-northwest along the southwestern coast of New Guinea, and was centred just off the coast of Indonesia's Pulau Dolak island by 00:00 UTC on 20 March. The system then began to track slowly southwestwards across the eastern Arafura Sea while its central barometric pressure steadily deepened. At 18:30 UTC, the Joint Typhoon Warning Center (JTWC) issued a tropical cyclone formation alert, and indicated that the likelihood of rapid intensification over the following days was high. On 22 March, the tropical low assumed a course towards the east, bringing it into an environment which was increasingly favourable for further development. Fuelled by sea-surface temperatures of approximately 29 °C (84 °F), the low-level circulation centre quickly consolidated as convective banding wrapped into the developing system. The JTWC indicated that the system had reached tropical storm strength on the Saffir-Simpson hurricane wind scale at 06:00 UTC, and gave it the designation Tropical Cyclone 16P. Six hours later, the system was officially upgraded to a Category 1 tropical cyclone and was assigned the name Nora by the BOM.  
  As Nora passed slowly to the north of the Wessel Islands in a weak steering environment, the already supportive environmental conditions became extremely favourable for strengthening. A co-located anticyclone in the upper troposphere provided excellent poleward and equatorward outflow channels for the system in an environment of low vertical wind shear, and sea surface temperatures and ocean heat content had both become favourably high. Nora began to rapidly intensify, reaching Category 2 strength on the Australian scale at 00:00 UTC on 23 March as a primitive eye began to emerge on visible-light satellite imagery. Shortly thereafter, Nora turned southeastwards under the influence of a strengthening high-pressure ridge to the east. The BOM upgraded the storm to a Category 3 severe tropical cyclone at 09:00 UTC, just after one-minute sustained winds had reached the equivalent of minimal hurricane intensity. Over the following three hours, Nora underwent explosive intensification, with maximum ten-minute sustained winds increasing by an average of 5 knots (9 km/h; 6 mph) every hour. Nora peaked in intensity as it entered the Gulf of Carpentaria, reaching high-end Category 3 severe tropical cyclone status on the Australian scale. The BOM estimated ten-minute sustained winds to be at 155 km/h (100 mph), gusting to 220 km/h (140 mph), with a minimum central pressure of 958 hPa (28.29 inHg). Concurrently, the JTWC indicated that one-minute sustained winds had reached 185 km/h (115 mph), equivalent to a Category 3 major hurricane on the Saffir-Simpson hurrica
caption: Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale
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