Developed thunderclouds are currently forming in central Tokyo. Be on alert for "guerrilla thunderstorms" through tonight.

2025年09月11日 14:51

According to meteorological observation data, thunderclouds are developing in central Tokyo and its surrounding areas, with some regions already experiencing short bursts of heavy rain and lightning. Even in areas where it was sunny, cloud development has significantly progressed from afternoon to evening, increasing the risk of sudden thunderstorms.tenki.jp
According to forecasts from the Japan Meteorological Agency and the Japan Weather Association, the atmosphere is considered "very unstable." Factors inducing this instability include the influx of warm, moist air, surface heating, and the approach of a pressure trough. These factors combined are promoting the development of thunderclouds.tenki.jp

Time Period: The risk is highest from late afternoon to evening, with the possibility of intermittent lightning and heavy rain continuing into the night. In areas where thunderclouds have already formed, it is necessary to be prepared for sudden weather changes.tenki.jp
Location: Particularly dangerous areas include urban districts including central Tokyo, low-lying areas in the suburbs, places with poor road drainage, underground facilities, underground shopping areas, and underpasses where water tends to accumulate. Even if it is sunny, sudden rain can occur if thunderclouds develop nearby.tenki.jp+1

Event	Details
Flooding and Inundation	Heavy rain in a short period may exceed drainage capacity, leading to flooding on roads and in underground facilities. The risk is particularly high in low-lying areas like underpasses.tenki.jp
Lightning and Electrical Hazards	The development of thunderclouds increases the risk of lightning strikes in areas where thunder and lightning are observed. Damage may occur to buildings, power lines, and outdoor equipment.tenki.jp
Poor Visibility and Traffic Disruptions	Heavy rain, hail, and strong winds can reduce visibility and make roads slippery. There is also the possibility of delays or cancellations in public transportation.
Human and Safety Risks	Outdoors, there is a risk not only of direct lightning strikes but also of accidents such as slipping into gutters or manholes, injuries from flying debris due to strong winds, and hail-related injuries.

Lightning Radar and Rain Cloud Radar: Utilize services that allow real-time confirmation of lightning activity and rain cloud movement. In Tokyo, "Lightning Radar (Live)" and "Guerrilla Thunderstorm Radar" are available, with some forecasts provided up to three hours ahead.tenki.jp+2Weather News+2
Warning and Advisory Information: Do not miss heavy rain and lightning advisories or warnings issued by the Japan Meteorological Agency, local governments, or the Japan Weather Association, especially information related to flooding and severe lightning.tenki.jp+1
Expected Precipitation: There are regions where heavy rain of several tens of millimeters per hour is expected in a narrow area, necessitating preparation for short-term heavy rain.tenki.jp

It is reassuring to make the following preparations:

Carry rain gear (folding umbrella, raincoat).
If you can adjust your outing time, avoid the periods of thunderstorms and heavy rain.
When outdoors, if you notice changes in the weather such as thunder, dark clouds, or cold winds, seek shelter indoors.
If using a car, consider detour routes as low roads, underground parking lots, and underpasses are prone to flooding.
Pay attention to your footing while walking. Areas like puddles, gutters, and manholes that become less visible are particularly dangerous.
Indoors, stay away from windows, walls, and electrical appliances. Prepare flashlights and mobile batteries in case of power outages.

Atmospheric Instability: The combination of warm, moist air, cold air, and the approach of a pressure trough strengthens updrafts, creating an environment conducive to the growth of cumulonimbus and lightning-producing clouds.tenki.jp
Frontal Conditions: The autumn rain front may be stationary or starting to move, leading to a continuous influx of moist air, triggering thunderstorms from afternoon to evening.tenki.jp
Impact of Topography and Urbanization: In urban areas with a lot of concrete and asphalt, the ground tends to retain heat, making it easier for updrafts to occur, which can promote the development of thunderclouds.

The risk of rain and lightning is expected to continue into tonight, with a possibility of similar atmospheric instability persisting into the following days.
Particular caution is needed during times of high temperature and humidity, especially during the evening to nighttime commute, where it is advisable to act with caution in anticipation of sudden weather changes.
Regularly check updates from meteorological agencies and local governments, and be prepared to respond to new warnings, advisories, and forecast changes.

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