Weakening El Niño will influence this year’s tropical storm season
Typhoons and hurricanes in 2019
The number of hurricane-strength tropical storms in the upcoming North Atlantic hurricane season and Pacific typhoon season will be broadly in line with the long-term average, according to an analysis of the forecasts available to date. That means that heavy hits from storms will remain a possibility, and a breather ‒ which many people had been hoping for ‒ is unlikely. Damage prevention measures therefore remain critically important.
The framework conditions:
Actual storm activity is very difficult to predict, as it is influenced by many factors. A key factor is the progress of the natural El Niño-Southern Oscillation (ENSO) climate oscillation in the Pacific. The influence that ENSO typically exerts on both the Atlantic and Pacific basins is expected to be relatively low in 2019 as the current weak El Niño phase is expected to further diminish over the coming months. In the Atlantic, El Niño phases tend to suppress hurricane activity. On the other hand, El Niño conditions in the Northwest Pacific frequently bring an above-average number of powerful typhoons.
Forecasts from May predict further weakening to a low El Niño intensity or even neutral conditions over the coming months, including the typical peak months for Atlantic hurricane activity, August to October. If this proves to be the case, El Niño would then possibly exert little or no influence on storm activity in the Atlantic, which could result in some forecasts having been slightly over-optimistic.
The U.S. National Oceanic and Atmospheric Administration (NOAA) recently predicted a near-normal 2019 Atlantic hurricane season, which matches Munich Re’s expectations as well. The NOAA prediction expected a combination of slightly warmer-than-average sea-surface temperatures in the tropical Atlantic and Caribbean Sea, and an enhanced west African monsoon. These features supportive of tropical cyclone formation and development would be counterbalanced by an expected ongoing weak El Niño phase.
Earlier publications from well-known forecast institutes considered it probable that hurricane activity in the North Atlantic this year would be slightly below average, mostly in line with the influence from a weak El Niño phase, while sea surface temperatures in the tropical Atlantic in the season August to October were expected to not exceed average levels.
Ultimately, all of the aforementioned expectations for hurricanes are close to long-term mean activity levels. By comparison, the period from 1950 to 2018 experienced an average of 11.6 tropical cyclones a year, of which an average of 6.3 reached hurricane strength (more than 64 knots or 119 km/h) and 2.6 major hurricane strength.
The typhoon season in the Northwest Pacific is also expected to produce a total number of tropical cyclones close to the long-term average of 26, with 17 tropical cyclones of typhoon strength being in line with the long-term average. Weak El Niño conditions could produce 10 severe typhoons (Categories 3–5), a slightly higher number than the long-term average of 9 typhoons.
Predicting the scale of potential losses is not possible at this stage, as there are any number of possible storm tracks and points of landfall. This can only be done a few days in advance when a storm is already approaching. Given the extreme losses from tropical cyclones over the years, a key factor in preventing damage over the long term is to ensure storm-resistant building construction.
All it takes is a single extremely powerful storm to hit a major urban area for devastatingly high losses to occur. Invariably, most losses are not caused by a high number of small storms but by a low number of very powerful ones. Globally, tropical cyclones have caused losses totalling US$ 1.3tn since 1980. Munich Re’s NatCatSERVICE database indicates that almost 90% of these losses (US$ 1.2tn) were caused by particularly extreme events. These included cyclones in the highest three categories with wind speeds of some 180 km/h (95 knots).
In 2017, North Atlantic hurricanes caused record losses of US$ 230bn, mostly in the United States. Last year, hurricanes Florence and Michael again caused billions of dollars of damage in the U.S., while it was Asia’s turn to suffer record losses in the magnitude of US$ 30bn from typhoons in the Northwest Pacific.