During April 5, 2017, the Fiji Meteorological Service started to monitor Tropical Disturbance 20F that had developed about to the northwest of the Fijian dependency of Rotuma. The system lied within an area of favourable conditions for further development with low to moderate vertical wind shear and warm sea surface temperatures of about. Over the next couple of days, the system moved south-westwards and gradually developed further, before it was classified as a tropical depression by the FMS during April 7. The United StatesJoint Typhoon Warning Center subsequently issued a Tropical Cyclone Formation Alert on the disturbance, as atmospheric convection consolidated around the system's elongated low level circulation center. During that day, the system was steered south-westwards towards Vanuatu and New Caledonia, by northeasterly winds located to the northwest of a subtropical ridge of high pressure. The system subsequently passed near or over the islands of Maewo and Ambae, before the JTWC initiated advisories on the depression and designated it as Tropical Cyclone 16P early on April 8. The system subsequently passed near or over Malakula, before the FMS reported that it had developed into a Category 1 tropical cyclone, on the Australian tropical cyclone intensity scale and named it Cook. After Cook was named, the cyclone steadily intensified further and developed a eye as it moved south-westwards towards New Caledonia. The FMS subsequently reported during April 9, that the system had become a Category 3 severe tropical cyclone, with peak 10-minute sustained winds of 155 km/h. The JTWC subsequently reported that the cyclone had peaked with 1-minute sustained wind speeds of 165 km/h, which made it equivalent to a Category 2 hurricane on the Saffir-Simpson hurricane wind scale. Cook subsequently made landfall on the Grande Terre Island of New Caledonia, between Houaïlou and Kouaoua at around 04:00 UTC on April 10 where it started weakening due to frictional forces. Cook subsequently emerged into the Coral Sea near Nessadiou a few hours later, where environmental conditions were not supportive for further development. As a result, Cook continued to weaken and started to transition into an extratropical cyclone, while atmospheric convection that surrounded the system decreased significantly. The cyclone subsequently rounded the western edge of the subtropical ridge and started to move southwards towards New Zealand. During April 11, the FMS issued its final advisory on Cook out of its area of responsibility and into New Zealand'sMetService area as a Category 2 tropical cyclone. During that day the JTWC also issued their final advisory, before MetService reclassified it as an extratropical cyclone during April 12. The system subsequently reintensified slightly as it continued to move southwards towards New Zealand, before it made landfall on the North Island's Bay of Plenty to the west of Whakatane during April 13. After making landfall, Cook moved south-southwest across the North Island, before it emerged into the Cook Strait during the next day. The system subsequently moved south-southwestwards to the east of the South Island, before the remnants were last noted during April 17, as they moved into the Southern Ocean.
Preparations and impact
According to Aon Benfield Inc. in January 2018, Cook was responsible for a death and a total of US$33 million in damage.
Vanuatu
Cook impacted northern, central and southern parts of Vanuatu between April 7–9, where it produced gale- to storm-force winds, heavy rain and widespread flooding, as well as rough seas. During April 7, the FMS reported that Cook posed an immediate threat to Vanuatu if it continued to develop. As a result, the Vanuatu Meteorology & Geo-Hazard Department started to issue tropical cyclone warnings, while the Vanuatu National Disaster Management Office issued a blue alert for the Banks, Penama and Sanma provinces. Over the next couple of days, these alerts were revised with Malampa and Shefa provinces placed under a red alert, before the all-clear was issued for the island nation during April 9. During Cook's impact on the island nation, all domestic and international airports were shut, while the NDMO formally evacuated over 1000 people to 13 shelters within the provinces of Shefa and Tafea as they were all living in flood-prone areas. Within Vanuatu no major damages were reported to buildings or infrastructure, however, significant and widespread damage was reported to fruit trees, cash and food crops such as bananas, manioc, peanuts, taro and yams. In response to the cyclone, the Government of Vanuatu activated its national emergency fund, however, it did not request assistance from the international community.
New Caledonia
After the cyclone had impacted northern Vanuatu, it moved south-westwards towards New Caledonia and became the first severe tropical cyclone to make landfall on its main island of Grande Terre since Cyclone Erica in 2003. During April 8, the Directorate of Civil Security and Risk Management placed the whole of New Caledonia on a pre-cyclonique alert for Cyclone Cook, which required all citizens to start making preparations for Cooks eventual landfall. Over the next couple of days the Directorate issued level-one and level-two cyclonique alert for most of the French territory, which required people to continue preparing before remain inside their homes or emergency shelters at the height of the storm. The territory was warned to expect very heavy rain, winds of up to, as well as a storm surge at high tide. As a result, the French education ministry cancelled some nationwide exams, while tourists were evacuated from seaside bungalows.
