Hurricane Rina (2017)

Hurricane Rina was the strongest Atlantic hurricane ever recorded in the month of December, as well as the tenth and final hurricane of the hyperactive 2017 Atlantic hurricane season. Rina was the latest Atlantic hurricane to form in a season since Lili in 1984. Rina developed from an upper-level trough over the subtropical eastern Atlantic in mid-December, and strengthened into a hurricane three days later as it accelerated northeastward in the mid-latitude westerlies. Rina eventually transitioned into a strong extratropical cyclone, and brought heavy rains and gusty winds to the British Isles.

Meteorological History
On December 14, an upper-level trough developed over the eastern subtropical Atlantic. It began developing some organized convection - though not very deep - early on December 15. The National Hurricane Center (NHC) issued a Special Tropical Weather Outlook at this time, noting there is a low chance of the system briefly developing into a subtropical cyclone before conditions became unfavorable. The convection slowly began to increase on the eastern semicircle, but convective activity near the center remained sparse. The system detached from a frontal zone early on December 16, and eventually acquired sufficient organization to be considered a subtropical storm at 18:00 UTC that day. However, NHC did not initiate advisories on Subtropical Storm Rina until 15:00 UTC on December 17, as they waited to see if the convection would persist.

Rina steadily organized after classification, already possessing winds of 45 mph. The NHC only expected slight strengthening with Rina, as moderate wind shear and cold waters of were expected to prevent the development of central convection. Rina transitioned into a tropical storm at 18:00 UTC on December 17, three hours after it was operationally classified. After transitioning into a tropical cyclone, deep convection increased markedly nearly the center, and microwave imagery indicates that a mid-level eye feature formed early on December 18. An ASCAT pass from that morning also showed that the wind field had shrunk considerably. Cloud tops began to cool quickly around a distinct warm spot, and it is estimated that Rina acquired hurricane intensity by 00:00 UTC on December 19, in contrast with predictions from the NHC. NHC Forecaster Lixion Avila said "It's beginning to look a lot like Rina-mas" in the discussion that upgraded Rina to a hurricane. Rina strengthened a little more that afternoon as a large eye feature cleared out, acquiring its peak intensity by 12:00 UTC that day with maximum sustained winds of 90 mph and a minimum pressure of 976 mbar. This made Rina the strongest December Atlantic hurricane on record. Rina began accelerating northward that day as convective cloud tops around the eye began to quickly warm. In addition, the cyclone became increasingly involved within a frontal zone. Rina transitioned into an extratropical cyclone by 06:00 UTC on December 20, while located north-northwest of the Azores.

After Rina transitioned into an extratropical cyclone, The United Kingdom Met Office (UKMET) designated the extratropical cyclone Storm Rina. Rina steadily weakened after the Met Office began tracking the system. Rina then eventually directly passed through Ireland and Great Britain as an extratropical cyclone, bringing heavy rains and gusty winds. Damage was light, and no fatalities were reported.