The western Pacific Ocean had been building up heat for a record 200
days without the churning from a single typhoon. The ocean basin that
spawns the strongest storms on Earth had been oddly quiet, but it's
making up for its slumber in a big way with Super Typhoon Nepartak.
This storm, which had maximum sustained winds of 175 miles per hour as of Wednesday morning, is a beast.
At that time, it was as close to a textbook case of an intense
typhoon as one typically sees in any season, or even multiple seasons,
and it illustrates how these storms grow and sustain themselves by
feasting on the energy drawn from a deep reservoir of warm ocean
waters.
Based on satellite imagery, Super Typhoon Nepartak has struck many
meteorologists as a near-perfect storm, to use the cliche phrase.
"There is a visual symmetry factor that goes into what makes a
tropical cyclone appear as what we might call "perfect,"" said Anthony
Sagliani, a meteorologist at Earth Networks in Maryland. "A small round
eye in the center of the storm surrounded by a ring of massive, deep
convection. Certainly Nepartak has that look. But to maintain that look
the storm actually needs several parameters to coincide for several
days," he said.
Hurricanes and typhoons (these are the same type of storms, but
located in different parts of the world and called different things) are
essentially giant heat engines, powered by the latent heat release from
evaporating warmth and moisture from mild ocean waters as well as humid
air masses.
Warm waters are present in abundance in the northwest Pacific Ocean
at this point. Water temperatures in the Philippine Sea are above 86
degrees Fahrenheit, or 30 degrees Celsius.
"This is partly because the region had previously been untouched by a
tropical cyclone for a record length of time," Sagliani said.
"Another parameter a storm like this needs in place is very low wind
shear. From the get-go, Nepartak has been impacted by no more than 6-12
mph shear. Its convective towers have no problem sustaining themselves
in that environment," Sagliani said in a Twitter message.
"Nepartak has a massive set of lungs"
The warm waters plus low shear helped the storm catapult from
Category 1 to Category 5 intensity within a 24-hour period. "The
upper-level conditions were perfect for rapid/explosive
intensification," said Ryan Maue, a meteorologist for the private
weather firm WeatherBell Analytics, in an email.
"Ocean heat content is anomalously high along the track of Nepartak
as well, likely contributing to the extreme intensification rates," Maue
said.
The heat goes into fueling massive thunderstorms that are tightly
packed around the center of the storm, in an area known as the central
dense overcast, or CDO.
Through Wednesday morning eastern time, such a feature was readily
apparent with Super Typhoon Nepartak. At the center of the CDO is the
storm's eye, where the air is descending and the air pressure is the
lowest. Nepartak features a relatively small eye, but that could change
over time.
The storm has also taken on the appearance of a so-called "annular"
tropical cyclone, with an absence of multiple spiral bands and the
presence of a large, dense area of thunderstorms extending well out from
the storm's center.
Also evident with this storm is its extraordinary "outflow channels" of air at upper levels of the atmosphere.
Tropical cyclone schematic, showing airflow within the storm.
Image: University corporation for atmospheric research
According to Sagliani, the healthy outflow from this storm has been particularly noteworthy.
"I think what impresses me the most about Nepartak, is its ability to
breathe. Nepartak has a massive set of lungs, with dual outflow
channels stretching both poleward and equatorward through almost 30
degrees of latitude from northern edge to southern edge," he said.
Essentially, at upper levels of the atmosphere, there is an area of
high pressure flowing counterclockwise, evacuating air from the storm.
Tropical cyclones lift a huge volume of air into the upper levels of
the atmosphere, where the air cools and dries. It is therefore necessary
for this air to be evacuated from the storm for hundreds to more than
1,000 miles away from the storm's center.
Infrared satellite image of Super Typhoon Nepartak on July 6, 2016.
Image: RAMMB/CIRA/CSU
Reconnaisance
aircraft are not flying into this storm as is the case for storms in
the Gulf of Mexico and Atlantic Ocean, so we don't know exactly what the
storm's intensity and minimum central air pressure is. The intensity
most likely peaked on Wednesday morning eastern time, likely to be
disrupted by internal dynamics prior to its arrival in Taiwan.
Meanwhile, meteorologists are using multiple methods using satellite imagery in order to estimate the storm's strength.
"Its near-perfect visual display should be taken as a warning like
the gorgeous colors and intricate patterns we see on venomous snakes and
fish," Sagliani said.
"While beautiful from the comfort of our computer screens, [it] is a
real, life-threatening typhoon that should be met with utmost concern
and preparation by those in its path."
Typhoon Nepartak is forecast to make landfall along the eastern coast
of Taiwan on July 8 or 9 as a Category 4 or 5 storm, capable of causing
extensive damage.
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