Hurricane William (2018)

**Hurricane William** was an unusual hurricane that developed in the northeastern Atlantic basin in late October of the 2018 hurricane season. The twenty-first named tropical storm and record-tying fifteenth hurricane of the extremely active season, it strengthened over waters thought to be too cold for tropical development. While it was a relatively weak and short-lived storm with no reported damage or fatalities, it was one of the most unusual hurricanes to ever develop in the Atlantic Ocean.

William was the second tropical system on record to incur any impact on the Canary Islands, the first being Tropical Storm Delta in 2005 (both of which had become post-tropical cyclones by the time of such impacts). It completely dissipated near Morocco, bringing much-needed rain to the region.

## **Meteorological history**

On the afternoon of October 28, the extratropical remnants of Subtropical Depression 23 were absorbed by a temperate frontal low, which was moving to the southeast of the Azores. The low pressure system gained a more concentrated circulation and lost its frontal structure after absorbing the extratropical remnants. The developing system became a tropical depression itself early on 29 October 900 miles (1448 km) southeast of El Hierro in the Canary Islands, the twenty-fourth system of the season. The depression kept its tropical characteristics briefly, as it degenerated into a tropical wave. The system completed an anticyclonic loop on 31 October before heading on a easterly course. The storm gradually regained the tropical characteristics of symmetry and a warm inner core and became a tropical storm early on November 1. Its transformation to a tropical system occurred over water temperatures cooler than 24 °C (75 °F), much colder than the 26.5 °C (80 °F) usually required for tropical development.

Soon after it became a tropical storm on 1 November near La Palma, with a ragged eye already present, the JMC officially named it Tropical Storm William and began to issue advisories once again on the system. An increase in the system's organization was accompanied by strengthening, and William reached its peak strength as a hurricane with 75 mph (120 km/h) winds later that day.

Hurricane William's organization was short lived as westerly wind shear began to erode the eye within hours. In response, the storm weakened to a tropical storm shortly thereafter. A broad low-level trough approached the storm from the northwest, pulling the convection northward as the storm's low-level center accelerated eastward. On 10 October, two brief bursts of convection surprised forecasters, but with the sea surface temperature as low as 21 °C (70 °F), the flares were not sustained. William continued to weaken as it approached the Canaries and became a tropical depression on 2 November. The system lost its tropical characteristics, and transitioned into an extratropical cyclone before completely dissipating the next day. Light impact was felt throughout the Canaries, particularly La Palma where the system made landfall.

## **Impact**

No damage or fatalities were reported. William's remnants was compared to normal rain events from non-tropical systems, with only 1 to 2 inches (25 to 50 mm) of rain falling.

## **Records and Naming**

Although Hurricane William developed in an unusual location in the northeastern Atlantic well away from where tropical cyclones are usually found, it is neither the northernmost forming nor the easternmost forming Atlantic tropical cyclone.

When Tropical Storm William formed on 1 November, it was the second-earliest in the season that the twenty-first tropical or subtropical storm had ever developed, and the second time ever that more than 20 tropical/subtropical storms formed in an Atlantic season; records beaten only by Hurricane Vince. William was also the second named "W" storm in the Atlantic since naming began in 1950, the first being Wilma. Both of the aforementioned storms are a part of the 2005 Atlantic hurricane season.