<s>
Tropical	B-Application
cyclone	I-Application
track	I-Application
forecasting	I-Application
involves	O
predicting	O
where	O
a	O
tropical	O
cyclone	B-Device
is	O
going	O
to	O
track	O
over	O
the	O
next	O
five	O
days	O
,	O
every	O
6	O
to	O
12hours	O
.	O
</s>
<s>
The	O
history	O
of	O
tropical	B-Application
cyclone	I-Application
track	I-Application
forecasting	I-Application
has	O
evolved	O
from	O
a	O
single-station	O
approach	O
to	O
a	O
comprehensive	O
approach	O
which	O
uses	O
a	O
variety	O
of	O
meteorological	O
tools	O
and	O
methods	O
to	O
make	O
predictions	O
.	O
</s>
<s>
The	O
weather	O
of	O
a	O
particular	O
location	O
can	O
show	O
signs	O
of	O
the	O
approaching	O
tropical	O
cyclone	B-Device
,	O
such	O
as	O
increasing	O
swell	O
,	O
increasing	O
cloudiness	O
,	O
falling	O
barometric	O
pressure	O
,	O
increasing	O
tides	O
,	O
squalls	O
and	O
heavy	O
rainfall	O
.	O
</s>
<s>
The	O
forces	O
that	O
affect	O
tropical	O
cyclone	B-Device
steering	O
are	O
the	O
higher-latitude	O
westerlies	O
,	O
the	O
subtropical	O
ridge	O
,	O
and	O
the	O
beta	O
effect	O
caused	O
by	O
changes	O
of	O
the	O
coriolis	O
force	O
within	O
fluids	O
such	O
as	O
the	O
atmosphere	O
.	O
</s>
<s>
The	O
methods	O
through	O
which	O
tropical	O
cyclones	B-Device
are	O
forecast	O
have	O
changed	O
with	O
the	O
passage	O
of	O
time	O
.	O
</s>
<s>
In	O
1895	O
,	O
it	O
was	O
noted	O
that	O
cool	O
conditions	O
with	O
unusually	O
high	O
pressure	O
preceded	O
tropical	O
cyclones	B-Device
in	O
the	O
West	O
Indies	O
by	O
several	O
days	O
.	O
</s>
<s>
Despite	O
the	O
issuance	O
of	O
hurricane	O
watches	O
and	O
warnings	O
for	O
systems	O
threatening	O
the	O
coast	O
,	O
forecasting	O
the	O
path	O
of	O
tropical	O
cyclones	B-Device
did	O
not	O
occur	O
until	O
1920	O
.	O
</s>
<s>
In	O
1937	O
,	O
radiosondes	O
were	O
used	O
to	O
aide	O
tropical	B-Application
cyclone	I-Application
forecasting	I-Application
.	O
</s>
<s>
In	O
the	O
1950s	O
,	O
coastal	O
weather	B-Application
radars	I-Application
began	O
to	O
be	O
used	O
in	O
the	O
United	O
States	O
,	O
and	O
research	O
reconnaissance	O
flights	O
by	O
the	O
precursor	O
of	O
the	O
Hurricane	O
Research	O
Division	O
began	O
in	O
1954	O
.	O
</s>
<s>
The	O
launch	O
of	O
the	O
first	O
weather	O
satellite	O
,	O
TIROS-I	O
,	O
in	O
1960	O
,	O
introduced	O
new	O
techniques	O
to	O
tropical	B-Application
cyclone	I-Application
forecasting	I-Application
that	O
remain	O
important	O
to	O
the	O
present	O
day	O
.	O
</s>
<s>
About	O
four	O
days	O
in	O
advance	O
of	O
a	O
typical	O
tropical	O
cyclone	B-Device
,	O
an	O
ocean	O
of	O
in	O
height	O
will	O
roll	O
in	O
about	O
every	O
10seconds	O
,	O
moving	O
towards	O
the	O
coast	O
from	O
the	O
direction	O
of	O
the	O
tropical	O
cyclone	B-Device
's	O
location	O
.	O
</s>
<s>
The	O
ocean	O
swell	O
will	O
slowly	O
increase	O
in	O
height	O
and	O
frequency	O
the	O
closer	O
a	O
tropical	O
cyclone	B-Device
gets	O
to	O
land	O
.	O
</s>
<s>
Two	O
days	O
in	O
advance	O
of	O
the	O
center	O
's	O
passage	O
,	O
winds	O
go	O
calm	O
as	O
the	O
tropical	O
cyclone	B-Device
interrupts	O
the	O
environmental	O
wind	O
flow	O
.	O
</s>
<s>
Within	O
36hours	O
of	O
the	O
center	O
passage	O
,	O
the	O
pressure	O
begins	O
to	O
fall	O
and	O
a	O
veil	O
of	O
white	O
cirrus	O
clouds	O
approaches	O
from	O
the	O
cyclone	B-Device
's	O
direction	O
.	O
</s>
<s>
Within	O
24hours	O
of	O
the	O
closest	O
approach	O
to	O
the	O
center	O
,	O
low	O
clouds	O
begin	O
to	O
move	O
in	O
,	O
also	O
known	O
as	O
the	O
bar	O
of	O
a	O
tropical	O
cyclone	B-Device
,	O
as	O
the	O
barometric	O
pressure	O
begins	O
to	O
fall	O
more	O
rapidly	O
and	O
the	O
winds	O
begin	O
to	O
increase	O
.	O
</s>
<s>
Within	O
an	O
hour	O
of	O
the	O
center	O
,	O
the	O
rain	O
becomes	O
very	O
heavy	O
and	O
the	O
highest	O
winds	O
within	O
the	O
tropical	O
cyclone	B-Device
are	O
experienced	O
.	O
</s>
<s>
When	O
the	O
center	O
arrives	O
with	O
a	O
strong	O
tropical	O
cyclone	B-Device
,	O
weather	O
conditions	O
improve	O
and	O
the	O
sun	O
becomes	O
visible	O
as	O
the	O
eye	O
moves	O
overhead	O
.	O
</s>
<s>
The	O
large	O
scale	O
synoptic	O
scale	O
flow	O
determines	O
70	O
to	O
90percent	O
of	O
a	O
tropical	O
cyclone	B-Device
's	O
motion	O
.	O
</s>
<s>
Knowledge	O
of	O
the	O
beta	O
effect	O
can	O
be	O
used	O
to	O
steer	O
a	O
tropical	O
cyclone	B-Device
,	O
since	O
it	O
leads	O
to	O
a	O
more	O
northwest	O
heading	O
for	O
tropical	O
cyclones	B-Device
in	O
the	O
Northern	O
Hemisphere	O
due	O
to	O
differences	O
in	O
the	O
coriolis	O
force	O
around	O
the	O
cyclone	B-Device
.	O
</s>
<s>
For	O
example	O
,	O
the	O
beta	O
effect	O
will	O
allow	O
a	O
tropical	O
cyclone	B-Device
to	O
track	O
poleward	O
and	O
slightly	O
to	O
the	O
right	O
of	O
the	O
deep	O
layer	O
steering	O
flow	O
while	O
the	O
system	O
lies	O
the	O
south	O
of	O
the	O
subtropical	O
ridge	O
.	O
</s>
<s>
The	O
larger	O
the	O
cyclone	B-Device
,	O
the	O
larger	O
the	O
impact	O
of	O
the	O
beta	O
effect	O
is	O
likely	O
to	O
be	O
.	O
</s>
<s>
When	O
two	O
or	O
more	O
tropical	O
cyclones	B-Device
are	O
in	O
proximity	O
to	O
one	O
another	O
,	O
they	O
begin	O
to	O
rotate	O
cyclonically	O
around	O
the	O
midpoint	O
between	O
their	O
circulation	O
centers	O
.	O
</s>
<s>
Usually	O
,	O
the	O
tropical	O
cyclones	B-Device
need	O
to	O
be	O
within	O
of	O
each	O
other	O
for	O
this	O
effect	O
to	O
take	O
place	O
.	O
</s>
<s>
It	O
is	O
a	O
more	O
common	O
phenomenon	O
in	O
the	O
northern	O
Pacific	O
Ocean	O
than	O
elsewhere	O
,	O
due	O
to	O
the	O
higher	O
frequency	O
of	O
tropical	O
cyclone	B-Device
activity	O
which	O
occurs	O
in	O
that	O
region	O
.	O
</s>
<s>
Small	O
wobbles	O
in	O
a	O
tropical	O
cyclone	B-Device
's	O
track	O
can	O
occur	O
when	O
the	O
convection	O
is	O
distributed	O
unevenly	O
within	O
its	O
circulation	O
.	O
</s>
<s>
Because	O
of	O
this	O
effect	O
,	O
forecasters	O
use	O
a	O
longer	O
term	O
(	O
6	O
to	O
24hours	O
)	O
motion	O
to	O
help	O
forecast	O
tropical	O
cyclones	B-Device
,	O
which	O
acts	O
to	O
smooth	O
out	O
such	O
wobbles	O
.	O
</s>
<s>
High-speed	O
computers	O
and	O
sophisticated	O
simulation	O
software	O
allow	O
meteorologists	O
to	O
run	O
computer	B-Application
models	I-Application
that	O
forecast	O
tropical	O
cyclone	B-Device
tracks	O
based	O
on	O
the	O
future	O
position	O
and	O
strength	O
of	O
high	O
-	O
and	O
low-pressure	O
systems	O
.	O
</s>
<s>
Combining	O
forecast	O
models	O
with	O
increased	O
understanding	O
of	O
the	O
forces	O
that	O
act	O
on	O
tropical	O
cyclones	B-Device
,	O
and	O
a	O
wealth	O
of	O
data	O
from	O
Earth-orbiting	O
satellites	O
and	O
other	O
sensors	O
,	O
scientists	O
have	O
increased	O
the	O
accuracy	O
of	O
track	O
forecasts	O
over	O
recent	O
decades	O
.	O
</s>
<s>
The	O
addition	O
of	O
dropwindsonde	O
missions	O
around	O
tropical	O
cyclones	B-Device
in	O
what	O
are	O
known	O
as	O
synoptic	O
flow	O
missions	O
in	O
the	O
Atlantic	O
Basin	O
decreased	O
track	O
error	O
by	O
15	O
–	O
20	O
percent	O
.	O
</s>
<s>
Starting	O
in	O
the	O
mid	O
to	O
late	O
1990s	O
,	O
research	O
into	O
tropical	O
cyclones	B-Device
and	O
how	O
forecast	O
models	O
handle	O
the	O
systems	O
led	O
to	O
substantial	O
improvements	O
in	O
track	O
error	O
.	O
</s>
<s>
In	O
addition	O
,	O
at	O
1700UTC	O
during	O
the	O
hurricane	O
season	O
,	O
a	O
medium-range	O
coordination	O
call	O
takes	O
place	O
between	O
the	O
Hydrometeorological	O
Prediction	O
Center	O
and	O
the	O
National	O
Hurricane	O
Center	O
to	O
coordinate	O
tropical	O
cyclone	B-Device
placement	O
on	O
the	O
medium-range	O
pressure	O
forecasts	O
6	O
and	O
7days	O
into	O
the	O
future	O
for	O
the	O
northeast	O
Pacific	O
and	O
Atlantic	O
basins	O
.	O
</s>
<s>
In	O
forecasts	O
,	O
the	O
National	O
Hurricane	O
Center	O
uses	O
a	O
track	O
forecast	O
cone	O
for	O
the	O
graphical	O
representation	O
of	O
the	O
uncertainty	O
in	O
its	O
forecasts	O
of	O
a	O
tropical	O
cyclone	B-Device
's	O
future	O
location	O
.	O
</s>
<s>
The	O
cone	O
represents	O
the	O
probable	O
position	O
of	O
a	O
tropical	O
cyclone	B-Device
's	O
circulation	O
center	O
,	O
and	O
is	O
made	O
by	O
drawing	O
a	O
set	O
of	O
circles	O
centered	O
at	O
each	O
forecast	O
point	O
—	O
12	O
,	O
24	O
,	O
36	O
,	O
48	O
,	O
and	O
72	O
hours	O
for	O
a	O
three-day	O
forecast	O
,	O
as	O
well	O
as	O
96	O
and	O
120	O
hours	O
for	O
a	O
five-day	O
forecast	O
.	O
</s>
<s>
The	O
National	O
Hurricane	O
Center	O
states	O
that	O
the	O
entire	O
track	O
of	O
the	O
tropical	O
cyclone	B-Device
"	O
can	O
be	O
expected	O
to	O
remain	O
within	O
the	O
cone	O
roughly	O
60	O
–	O
70%	O
of	O
the	O
time.	O
"	O
</s>
