Quieter than usual Atlantic hurricane season predicted

The North Atlantic is likely to experience two major hurricanes in 2023 with about 12 named storms, according to an analysis of leading forecasters and researchers.

But the North Pacific typhoon season is expected to be more severe than usual, according to an analysis from Munich Re, released on the first day of the 2023 hurricane season.

The re/insurer said it expected six named storms in the North Atlantic, but warned the forecast was complicated by the conflicting effects of a stronger than usual El Niño phenomenon and unusually high water temperatures in the tropical North Atlantic.

While El Niño is expected to reduce hurricane severity in the Atlantic, higher water temperatures contribute to hurricane strength. Munich Re said it was not clear which of the factors would dominate, or if they would cancel each other out.

The possibility of a quieter than usual hurricane season comes after several active years. In 2022, there were 14 tropical cyclones in the North Atlantic, of which six were hurricanes and two were category 3–5, which are considered major hurricanes. The most devastating storm of the year was Hurricane Ian, with overall losses of $100 billion, of which roughly $60 billion was insured. 2020 was a record hurricane season with 30 storms, Munich Re said.

The company said of 2023: "Around six tropical cyclones could develop into hurricanes, and two into severe hurricanes with wind speeds in excess of 110 mph (177 km/h).

"This estimate more or less matches predictions from leading forecasting institutes and corresponds to the long-term annual average from 1950 to 2022 (12.2 named storms, of which 6.4 were hurricanes and 2.6 major hurricanes).

"Since the mid-1990s, storm activity during the cyclical warm phase in the North Atlantic has been slightly higher than this, with an average of 15.7 tropical storms, of which 7.7 were hurricanes and 3.6 major hurricanes."

It added: "Current predictions for this year anticipate sea surface temperatures of up to 1°C above average during the main months of hurricane activity from August to October. Even now, temperatures in the tropical North Atlantic are showing a significant increase.

"A warmer than usual tropical North Atlantic is known to create generally more favourable conditions for the development and intensification of hurricanes. It also ensures lower air pressure and weaker trade winds, which likewise contribute to an environment favouring hurricanes."

However, it said the El Nino phenomenon, also known as ENSO - El Niño/Southern Oscillation - was expected to counter this.

It said: "Even though this is actually a temperature swing in the Pacific, it exerts a strong influence on extreme weather in very distant regions.

"After three years with La Niña conditions, which favour hurricanes, a swing to what may become a strong El Niño phase is expected in the late summer.

"El Niño years are accompanied by strong winds at high altitude over the North Atlantic. This is known as vertical wind shear, which inhibits cyclones because it literally tears storm systems apart. According to current forecasts, vertical wind shear is likely to increase to a high level during the main period of the hurricane season."

But it added: "Although the models are predicting a strong El Niño phase for the late summer with relative certainty, the level of hurricane activity will also depend heavily on the current high ocean temperatures. These conflicting signals make it difficult to provide a reliable forecast for this year’s hurricane season."

Munich Re said El Niño was expected to have the opposite effect on the typhoon season in the western part of the North Pacific from the North Atlantic.

It added: "El Niño is likely to favour greater typhoon activity here in 2023. In the period 1980 to 2021, the region experienced an average of 26 named storms per year, 16 of which were typhoons and nine major typhoons in category 3–5.

"The heaviest losses from typhoons regularly occur in Japan, but there is also a rising loss trend in China and India. The costliest typhoons in Japan to date – Jebi in 2018 and Hagibis in 2019 – with losses in the tens of billions, both were influenced by El Niño conditions.

"The landfall risk in Japan is slightly higher in El Niño years. For Japan, though, it is essential to distinguish between two El Niño types: the “classic” basin-wide El Niño and the so-called “El Niño Modoki”, where the warming pattern is particularly strong in the Central Pacific. In El Niño Modoki years, the landfall risk in Japan and Korea is particularly high, although this year a classic El Niño is expected to form."

Munich Re's analysis was supported by a forecast from Tropical Storm Risk, which forecast a below average season with 13 named storms and six hurricanes, of which two are expected to be Category 3 or above.

TSR said it expected El Nino to suppress tropical storm activity.