September is usually the most active month of the year for tropical cyclones worldwide, but in 2018 there were 21 named tropical cyclones active at some point during the month – just one short of the record of 22 set in 1966.

Atlantic

Despite conditions in the tropical Atlantic and Caribbean not being as favourable for tropical cyclone formation as in 2017, the region still saw a total of seven named storms in September, the strongest of which developed outside of the deep tropics. Florence was the most significant hurricane bringing over 750 mm rain and severe flooding to North Carolina in the USA. Gordon made landfall as a tropical Storm over southern USA and Helene remained in the eastern Atlantic and affected the UK and Republic of Ireland as a ‘post-tropical’ storm. Isaac was a weakening tropical storm as it encountered the unfavourable conditions in the Caribbean, but still brought a spell of heavy rain to some islands as did Kirk a couple of weeks later. The latter produced some severe flooding in Barbados. Joyce meandered near the Azores for a few days and as the month ended Leslie was set to move slowly over central parts of the subtropical Atlantic for several days to come.

Hurricanes Florence and Helene with Tropical Storm Isaac seen at
1345 GMT 10 September 2018 (Credit: RAMMB/CIRA).

Eastern Pacific

The eastern Pacific hurricane season in 2018 has been very active. In September Hurricanes Miriam and Norman remained far from land, but Olivia brought heavy rain and flooding to parts of Hawaii as it weakened on its journey into the central Pacific. Paul was a weak tropical storm, but as the month ended Tropical Storm Rosa, formerly a hurricane, threatened to bring flash flooding to parts of north-western Mexico, southern California and Arizona after landfall. Tropical Storm Sergio is expected to become a hurricane over open waters during early October.

Western Pacific

The month started with Typhoon Jebi bringing strong winds and rain to parts of Japan. Mangkhut developed soon after and ploughed a track across the northern Philippines as a powerful typhoon causing loss of life and severe damage from wind and flooding.  Mangkhut went on to also have severe impacts over Hong Kong. Barijat reached southern China as a weak tropical storm, but the next in line was Trami which became another powerful typhoon. After moving slowly for several days east of Taiwan, it eventually crossed the Ryukyu Islands and into the main islands of Japan at a similar location to Jebi a few weeks before. As the month ended, Typhoon Kong-rey looked set to head towards Japan or South Korea during the first week of October.

Typhoon Mangkhut seen at 0800 GMT 13 September 2018 (Credit: RAMMB/CIRA).

Elsewhere in the Globe

Walaka became the first storm to be named in the central Pacific region for two years and quickly developed into a hurricane. In the Bay of Bengal a depression strengthened into Tropical Storm Daye just before landfall and brought flooding impacts to parts of India. There was also an unusual September tropical storm in the South Pacific near the Solomon Islands named Liua.

In addition to the named tropical storms described above there were other weaker tropical depressions in the Atlantic, east and west Pacific and the south Indian Ocean. Finally, the Mediterranean saw what is often referred to as a ‘medicane’, which made landfall over Greece as a likely tropical or subtropical storm bringing severe flooding to some regions. Since this was not officially named by any tropical cyclone warning agency, it has not been included in the total of 21 named storms for the month of September.

Mediterranean Storm at 1130 GMT 29 September 2018

Further Information

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