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Typhoon Ma‐on (Japan) A typhoon is a mature tropical storm that develops in the northwestern part of the Pacific Ocean between 180°E and 100°E. This region is referred to as the northwest Pacific basin and covers the area of ocean north of the equator and west of the International Date Line, including the South China Sea. This is the busiest cyclone basin in the world, averaging 25.7 tropical storms a year and 16 typhoons a year from 1968‐
89. Typhoons are known as cyclones in the Indian Ocean and the Bay of Bengal. Outside of these areas, they are simply known as hurricanes. There are six main criteria that must be fulfilled before a typhoon will form: sufficiently warm surface sea temperatures, atmospheric instability, high humidity in the troposphere, a pre‐existing low level focus or disturbance, low vertical wind shear, and enough Coriolis force to develop a low pressure centre. Wind shear is generally accepted by pilots to be where the wind changes horizontal direction by more than 30 knots (15m/s), although that value is higher for airliners, where it is 45 knots (22m/s). The Coriolis Effect is defined as the deflection of moving objects when they are viewed in a rotating reference frame. This essentially means that the Earth’s spin causes a movement of air in a clockwise direction in the northern hemisphere and an anticlockwise direction in the southern hemisphere. It is the Coriolis Effect which makes it necessary for long distance planes to start their journey slightly off‐
target, so that the rotation of the Earth will bring them back towards their destination. Typhoons form when strong clusters of thunderstorms drift over warm ocean waters. The storm air combines with the warm ocean air and rises, causing low pressure at the ocean surface. As trade winds hit the winds within the storms, The Coriolis Effect causes the winds to gyrate and spin. This makes the hot air rise faster and creates low pressure not only at the surface but also above it. It can take anywhere from a few hours to a few days for storms to develop into a typhoon. Typhoon Ma‐on was spotted as remnants of a storm near Wake Island on July 9th. It is currently affecting most of southern Japan. It is the second typhoon in the 2011 Pacific Typhoon Season. From the remnants of the storm, the system slowly organized as it developed low‐level circulation. With low wind shear and generally favourably climatic conditions requireed for a typ
phoon to fo
orm, tropicaal cyclone fforecast mo
odels predicted th
that a ttropical cycclone would
d develop ffrom the syystem. On July 11 , the Joint Typ
phoon Warnin
ng Centre (JJTWC), run by the US Navy and A
Air Force an
nd located iin Pearl Harbour, issued aa tropical ccyclone form
mation alerrt, and a few hours latter the Japaan Meteoro
ological Agencyy (JMA) reported the fformation o
of a tropical depressio
on about haalfway betw
ween Wake Island and tthe Northern Marianaas Islands, w
which are aabout threee‐quarters o
of the om Hawaii tto the Philippines. way fro
The dep
pression travelled west on the trrade winds after its fo
ormation. TThe circulation was initiallyy not very faast or well‐‐defined, an
nd dry air cconditions m
made its co
onvection w
weak. However better co
onditions w
were found when it tu
urned north
hwards and
d the JMA th
upgraded it to Tro
opical Storm
m Ma‐on on
n July 12 . The storm intensified
d at a slowe
er than averagee rate for the region, but en eye was identified on t
July 13th
. The same day, the JMA upgraded it to a severe tropical storm, and on the 14
4th it was upgraded to
o a typhoo
on. By then,, it was abo
out 970km ssoutheast o
of Iwo Jima. By the 15th, Typho
oon Ma‐on had develo
oped a well‐defined eye, an
nd the JTWC
C estimated
d 1 minute sustained winds of 135mph. The nextt day, JMA estimated 10 minute sustained winds of 11
10mph. The
e same day Maa‐on started
d travellingg northwestt. After M
Ma‐on attained tropicaal storm staatus, the Gu
uam Nation
nal Weatheer Service isssued a tropical storm watch for threee areas in the Pacificc. It was lateer upgraded to a tropical storm w
warning aftter Ma‐on b
became a typhoon, which was caancelled wh
hen the sto
orm passed south of th
he islands. The typhoo
on caused h
high wavess and storm
m surges in G
Guam, and in JJapan it briefly made landfall in ssouthern Tokushima P
Prefecture.. Persisteent rain cau
used by thee typhoon o
over southe
ern Japan h
has affected
d rail servicces and has cau
used over 1
120 flights o
on Wednessday to be ccancelled, in addition to the 400 cancelled on Tuessday. People have beeen warned tto be on th
he alert for mudslides and maji, Kochi P
Prefecture,, accumulatted precipittation meaasured flooding. In the village of Um
851.5 m
mm on Tuesday, which
h is a one‐d
day record in Japan. B
Because Maa‐on is so slow movingg, the total rainfall from the storm
m on the Pacific side o
of western and easterrn Japan iss now at ovver 1000mm
m. As of W
Wednesday morning, ttorrential raain and stro
ong winds h
had injured
d over 55 people and one is reporteed missing.