Around 27 typhoons strike Japan each year on average,
causing damage with gusty winds and torrential rain across the
nation. Torrential rains often cause floods, mud flow, etc.
In Tokyo, large typhoons have caused high tides and flooded
major river systems to submerge low grounds in the east, while
small and medium rivers like Shakujii and Kanda rivers have
also flooded areas of recent development. TMG has
implemented measures including modifying river routes,
establishing reservoirs, and developing floodwalls, thus
achieving a significant reduction in damage. Yet, frequent
record-breaking downpours, combined with urbanization, are
causing urban flooding, symbolized with water damage to
basement floors and subway facilities.
In order to minimize damage from typhoons and heavy rain,
we must equip ourselves with correct knowledge on storm /
flood damage and take precautions.
Torrential rains
Typhoon
Alerts / Warnings
Torrential rains represent massive
precipitation in a localized area.
They typically involve heavy rain and
thunder, lasting for many hours any
time of the day, be it midnight or
dawn.
Typhoon represents a tropical
low pressure system that
appears in the northwest
Pacific, with the maximum
velocity of at least 17 m/sec
(34 knots).
Alerts are issued when the
applicable weather system may
cause damage, whereas
warnings are issued when it
may cause serious damage.
Alert / warning issuing authorities and their jurisdictions
Alerts and warnings are issued for specific areas, if it is possible to identify areas that may suffer damage as a result of weather and other phenomena.
Issuance
authority
Jurisdiction
Tokyo
Meteorological
Agency
Northern
Izu Islands
Hachijo
observatory
Southern
Izu Islands
Local district name
used in
announcement
Applicable municipalities
Central east
Taito-ku, Sumida-ku, Koto-ku, Arakawa-ku,
Adachi-ku, Katsushika-ku, Edogawa-ku
Central west
Chiyoda-ku, Chuo-ku, Minato-ku, Shinjuku-ku, Bunkyo-ku, Shinagawa-ku,
Meguro-ku, Ota-ku, Setagaya-ku, Shibuya-ku, Nakano-ku, Suginami-ku,
Toshima-ku, Kita-ku, Itabashi-ku, Nerima-ku
Tama south
Hachioji-shi, Machida-shi, Hino-shi, Tama-shi, Inagi-shi
Tama north
Tachikawa-shi, Musashino-shi, Mitaka-shi, Fuchu-shi, Akishima-shi, Chofushi, Koganei-shi, Kodaira-shi, Higashimurayama-shi, Kokubunji-shi,
Kunitachi-shi, Nishitokyo-shi, Komae-shi, Higashiyamato-shi, Kiyose-shi,
Higashikurume-shi, Musashimurayama-shi
Tama west
Fussa-shi, Hamura-shi, Ome-shi, Akiruno-shi,
Nishitama-gun (Mizuho-machi, Hinode-machi, Hinohara-mura, Okutama-machi)
Oshima Island
Oshima-machi
Niijima Island
Toshima-mura, Niijima-mura, Kouzushima-mura
Miyake Island
Miyake-mura, Mikura-mura
Hachijo Island
Hachijo-machi, Aogashima-mura
Note: Use the phrase “surrounding waters” to indicate the entire waters for the applicable district.
Main alerts and warnings for storm / flood damage, issued by the Japan Meteorological Agency and Hachijo observatory, and their issuance criteria
Meteorological warning
Meteorological alert
Type
Region
Issuance criteria
When the average velocity is projected to be over 13m/sec (or 16m/sec if observed by the Hachioji observatory)
Tokyo
Strong
wind Northern Izu Islands When the average velocity is projected to be over 15m/sec (or 12m/sec if observed by the Oshima observatory)
alerts Southern Izu Islands When the average velocity is projected to be over 15m/sec
Heavy Tokyo
rain
alerts
Central and Tama
north / south
Tama west
Precipitation in 3 hours
Precipitation in 24 hours
Over 30mm
Over 70mm
Over 130mm
Over 50mm
Over 90mm
Over 180mm
Over 30mm (total precipitation of 70mm)
Over Kouzushima Island Niijima Island of 20mm
Over 30mm
Over Miyake Island of 20mm
Over 50mm
Over Kouzushima Island Niijima Island of 40mm
Over 60mm
Over Miyake Island of 35mm
Over 150mm
Over Kouzushima Island Niijima Island of 80mm
Over 150mm
Over Miyake Island of 100mm
When the average velocity is projected to be over 25m/sec
Strong
wind
warning
Heavy Tokyo
rain
warning
Precipitation in 1 hour
When the average velocity is projected to be over 25m/sec (or 20m/sec if observed by the Oshima observatory)
When the average velocity is projected to be over 30m/sec
Central and Tama
north / south
Tama west
Precipitation in 1 hour
Precipitation in 3 hours
Precipitation in 24 hours
Over 50mm
(total precipitation of 80mm)
Over 90mm
Over 200mm
Over 70mm
Over 120mm
Over 250mm
Over 50mm (total precipitation of 150mm)
Over Kouzushima Island Niijima Island of 40mm
Over 50mm (total precipitation of 150mm)
Over Miyake Island of 30mm
Over 100mm
Over Kouzushima Island Niijima Island of 80mm
Over 100mm
Over Miyake Island of 60mm
Over 300mm
Over Kouzushima Island Niijima Island of 140mm
Over 300mm
Over Miyake Island of 200mm
Note: The figures shown as issuance criteria have been defined based on past correlation between meteorological conditions and disaster frequency in Tokyo, and
should be used as a guide in predicting the likelihood of weather-induced damage under certain meteorological conditions.
High tide
Lands near a shoaling
beach, at the end of a bay
or at the mouth of a river
When the tide is high, the sea level is
likely to surge at a shoaling beach that
has the seabed dropping suddenly off
the coast,
and land at
the end of a
bay.
Coastal land close to sea level
Be aware of low grounds positioned
below the average sea level at high tide.
Such areas are prone to serious flood
damage if sea walls give way.
Flooding
Landslide
Alluvial plain
Reconstructed land
Flooding is likely at “delta plains”
created near the mouth of a river with
sand and soil carried in the river water,
or at “flood plains” created through
accumulation of sand and soil as a
result of repeated flooding.
Tracts of land, developed on a hillside, have
unstable soil properties
and shapes. Torrential
rain could weaken and
collapse the foundation.
Alluvial fan
Riverbank
Areas along rivers and lands that
used to form riverbanks, are vulnerable
to flooding at the time of torrential rain.
Landslides, caused by a localized rainstorm
at a mountainous
region, may strike an
alluvial fan at the foot
of the mountain.
Mountainous region
Sharp slopes at the gradient of over 30 degrees and
height of over 5 meters,
may cause landslide with
heavy rain. Mountainous
areas with low vegetation
density are also prone to
landslide.
Typhoons and rainstorms should not be taken lightly
although their arrival can be predicted. It is important to take
precautions to minimize storm / flood damage.
Outside preparation
Securely lock all windows and rain screens, and reinforce
with timber from outside if necessary.
Reinforce garden trees and fences.
Clear gutters and storm-water pipes for better drainage.
Check and reinforce the stay cables and bracing for TV
antenna.
Affix or store indoors objects that may be blown away
with winds.
Inside preparation
Checks on emergency supplies
Flashlight, portable radio (batteries), first aid kit,
clothes / valuables, emergency foods, portable cook-top
Safety measures from inside
Close rain screens, apply packing tape on windowpanes
to prevent the glass from shattering, and close curtains /
blinds in case of any airborne objects flying in through the
windows.
Water
Set aside drinking water in case the water supply
becomes suspended, and fill the bathtub with water for
miscellaneous household use.
Evacuation locations
Each municipality has a list of designated evacuation
areas. Check your designated area in case evacuation is
required.
Attention to typhoon information
When a typhoon is approaching, meteorological authorities issue upto-date typhoon information, which is broadcast on TV and radio.
When you learn of an approaching typhoon, conduct a safety check
around the house.
Attention to alerts / warnings
Alerts / warnings are issued when the approaching typhoon is
expected to deliver damage. Use TV and radio to be aware of the
latest alerts / warnings.
Staying away from hazardous areas
It becomes difficult to see the edges of rain-swollen streams and
gutters, causing many people to miss the steps and fall in. They also
trigger mudslides and landslides.
Inspection of emergency supplies
Check your emergency supplies.
Evacuation preparation
Check the route to your evacuation area, method of
evacuation instructions, and cooperative arrangement
with neighbors, so as to be well prepared when an
evacuation order is actually issued.
Evacuation
Be well prepared for swift evacuation when you feel imminent
danger or are instructed to evacuate by disaster management
authorities.
Make sure to put out any fires and flames before evacuation.
Keep your luggage to a minimum and carry it on your back
when evacuating, so that both of your hands are available for
emergency protection.
Act prudently according to the instructions of the leader.
At the evacuation site
Follow the instructions of the leader,
rather than act on your personal
judgment.
Continue to pay attention to typhoon
information, alerts and warnings.