October is shaping up to be a record for typhoons in Japan, with five, and perhaps even six, expected to have hit before the month is out.
A powerful typhoon, the 27th this season, is forecast to approach southern Kyushu as well as the main Honshu island this weekend, hard on the heels of one last week that was the most powerful storm to batter Japan in a decade.
Even as October draws to a close, two typhoons are on the horizon. One is Typhoon No. 27, which is set to be the fifth to come near Japan this month. Typhoon No. 28 was also confirmed to have formed on Oct. 21, but it is too early to predict whether it will pound these shores.
According to the Japan Meteorological Agency, an average 1.5 typhoons approach in October. The most until now have been the four in 1955 and 2012.
A one-degree rise in ocean surface temperature near the equator is responsible for the large number this October, according to Akiyoshi Wada, a senior researcher in the Typhoon Research Department of the Meteorological Research Institute.
Typhoons generally form to the northwest of a warm ocean, and more are generated as the ocean temperature rises.
Typhoons then generally move in a northwest direction and swipe the eastern coast of the Philippines.
In normal years, typhoons passing that area during summer churn up the ocean water. As cooler water from deeper in the ocean is mixed in, ocean temperatures tend to drop.
However, this year, ocean temperatures in that area were also higher than normal in September. Typhoons intensify in force as they pass over a warmer ocean.
"Bad conditions that lead to the formation of many typhoons and allow the typhoons to strengthen easily have been aligned this year in the Pacific," Wada said.
There are other conditions that have made it easier for the typhoons to threaten Japan this year.
JMA officials said the high pressure system over the Pacific has been stronger than usual this year. Typhoons pass along the western periphery of that system, making it easier for typhoons to move upward toward Japan.
Also, in normal years, westerlies that have moved southward have kept typhoons much farther south of Japan before they move eastward. This year, however, those westerlies have remained at more northly latitudes, which allows the typhoons to move northward.
JMA forecaster Norihisa Fujikawa said, "If southern winds from the typhoon blow into the front, it causes heavy rain. That is the basic pattern for heavy rain brought by autumn typhoons."
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