Fewer typhoons, longer rainy season possible…big forecast! What will happen this summer?

Probability is 60%… If an “El Nino Phenomenon” occurs, low temperatures and lots of rainfall are possible.

Summer days in many places even though it is April. Will this summer be as hot and humid as last year…?

On the 10th of this month, the Japan Meteorological Agency released an “El Nino Monitoring Bulletin. It says there is a 60% chance that an El Nino phenomenon will occur through this summer. What happens when an El Nino phenomenon occurs?

The El Niño phenomenon refers to an increase in sea water temperature off the coast of Peru.

When an El Niño phenomenon occurs, the overhang of the Pacific High pressure system weakens during the summer near Japan, resulting in cooler temperatures and less sunshine hours. During the rainy season, the high pressure that pushes up the rainy season front weakens, so the rainy season may last longer. Conversely, in winter, the winter pressure pattern of high in the west and low in the east tends to weaken, and temperatures tend to be higher.

says Sayaka Ikeda, a weather forecaster.

Last summer, Tokyo experienced a heat wave of more than 35°C for nine consecutive days. According to Ikeda, this was due in large part to the “La Niña phenomenon” that occurred from the fall of ’21 to the winter of ’23.

The lowering of sea water temperature off the coast of Peru makes it easier for the Pacific High to overhang during the summer, opposite to the case of the El Niño phenomenon, and the temperature tends to be higher. Last summer, the Tibetan High also extended out, making the Japanese archipelago look like two layers of bedding, and the heat wave continued.

This summer, however, we are experiencing the El Niño phenomenon. Will it stay cool?

We cannot let our guard down. I think it is unlikely that we will have the heat wave and extreme heat like last year, but the base temperature has been rising due to global warming to begin with.

The most recent El Niño event occurred in summer was in ’15. Generally speaking, it is supposed to be a cool summer, but Tokyo experienced eight extremely hot days of 35°C or higher from July 31 to August 7.

Incidentally, 30 years ago in 1993, the highest temperature was 32.9°C in August. It is hard to believe that the hottest day was in the 32°C range. The base temperature has certainly been rising.

Fewer typhoons, rainy season may last longer

An El Niño phenomenon is considered to have occurred when sea water temperatures in the “monitoring area” off the coast of Peru rise above +0.5°C above the reference value and are expected to continue for at least one year. When the temperature drops below -0.5°C, it is defined as a La Niña event.

The larger this difference in sea surface temperature, the greater the impact. When El Niño occurs, the number of typhoons may decrease because the pressure pattern makes it difficult for cumulonimbus clouds to develop off the coast of the Philippines.

In 2010, 25 typhoons occurred, including Typhoon No. 14, which flooded a river in Nichinan City, Miyazaki Prefecture, and submerged the tracks of the Tokyo Metro Tozai Line between Iidabashi and Kudanshita stations in Tokyo. In addition, Typhoon No. 15 caused a 24-hour rainfall of 416.5 mm in Shizuoka City. It caused major damage, including power outages in approximately 119,000 households. Is that going to happen this year?

I think the number of outbreaks will be fewer, but the course is a problem. When the Pacific High is overhanging, typhoons often avoid hitting Honshu because they travel around the edge of the high.

Could we see heavy rainfall like last year?

One of the reasons for the increase in the amount of rain that falls at one time is the effect of global warming. Higher temperatures increase the amount of moisture that can be contained in the air, making it easier for heavy rainfall to occur.

What about the rainy season?

If an El Niño phenomenon occurs and the high pressure system is weak, the rainy season may be prolonged. Along with the prolonged rain, we will need to be careful of heavy rains.

Although the possibility of a heat wave as intense as last year’s will be reduced, we cannot let our guard down this summer. The next “El Niño Monitoring Bulletin” is scheduled to be released on May 12.

Sayaka Ikeda qualified as a meteorologist in 2003 and has appeared on NHK TV’s “Asaichi” (Tuesday) and TBS Radio’s “Seikatsu wa Odoru,” “Komigito,” “Session,” “Saturday Wide Radio TOKYO: Nights no Chaki-Chaki-Daihoso,” etc. She is also a member of the Japan Meteorological Agency (JMA), the Japan Meteorological Agency (JMA), and the Japan Meteorological Agency (JMA).