Transcript W6-3: Thoughts and Data about Hurricanes

“It's tough to make predictions,
especially about the future”
HOfail all
WEVER…
“You can see a lot by looking”
Yogi Berra
Formation by Organized Convection
Figure 16.5A
Figure 16.5B
One theory explains that hurricane formation requires cold air above an
organized mass of thunderstorms, where the release of latent heat warms
the upper troposphere, creates high pressure aloft, which pushes air
outward and causes a low to deepen at the surface.
Air moving toward this low intensifies the cycle.
Formation by Heat Engine
Another theory of hurricane development proposes that
a heat engine cycle, fueled by warm moist input air and
the release of heat when it converts to cool dry air.
Differences in the input and output temperatures
determine the amount of work on the ocean and winds
that is performed.
Hurricane Stages of Development
The initial
components of a
hurricane may
form as a tropical
disturbance, grow
into a tropical
depression when
winds exceed 20
knots, become a
tropical storm
when winds
exceed 35 knots,
and finally then
qualify as a
hurricane when
winds exceed 64
knots.
Figure 16.6
Tropical cyclone structure
Maintaining
the coherent
outflow is key
to rate of
hurricane
pressure
evolution
• Hurricane characteristics
• Sustained winds greater than 120 km/hr (74 mph)
• Average diameter = 600 km (350 mi)
• Central pressure = ~ 950 mb to 870 mb
Outflow at top driven by internal
pressure increase due to latent
heat addition to the column
Subject to Dust Suppression
Tropical cyclone genesis areas and related storm tracks
11
Conditions in Active Seasons
This inter-related set of conditions has strong links to tropical climate
factors. CPC has an extensive monitoring program to assess and predict
these conditions and the associated climate factors.
www.cpc.ncep.noaa.gov/products/hurricane/
13
Better Visualization
1950-1980

1950 - 1980
1990 - 2012
1990-2012 Cat 3 heat map
1950-1980 – feature absent
Strong Primary Peak (sep 10) – but
also an Oct 18 secondary peak
Driven by thunderstorms in
Caribbean
The
Anomalous
Path of Sandy
Erratic Paths of Hurricanes
August – October SSTs: Ten Most Active – Ten Least Active Atlantic
Hurricane Seasons Since 1950
Current SST Pattern – Mid-April 2015
April SST Pattern Correlated with
Seasonal Atlantic ACE
b – La Niña
a – El Niño
El Niño and La Niña
El Niño and La Niña reflect large year-to-year changes
in tropical Pacific Ocean temperatures.
El Niño
La Niña
Increased Wind Shear, Fewer Hurricanes
Decreased Wind Shear, More Hurricanes
Warm, Wet
More
Shear
El Niño suppresses hurricane activity
by increasing the vertical wind shear.
Strong wind shear can prevent
hurricanes from forming, and can
also kill an existing hurricane.
Cool, Dry
Less
Shear
La Niña favors more hurricane
activity by decreasing the vertical
wind shear.
www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml
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Tropical Multi-Decadal Signal
Associated with Atlantic High-Activity Era
Warmer
Warmer
Stronger West
African Monsoon
This climate pattern lasts 25-40 years, and produces key ingredients of a highactivity era for Atlantic hurricanes: warmer waters, reduced wind shear, and
favorable winds that strengthen cloud systems coming from Africa.
•ACE index measures overall season strength by accounting for the combined
number, intensity and duration of tropical storms and hurricanes.
•ACE=Sum of squares of maximum sustained surface wind speed (measured
6-hourly) for all named storms while at least tropical storm strength.
THC (or AMO)
STRONG
THC (or AMO)
WEAK
H
H
3
1
2
Courtesy of John Marshall (MIT)
Annual Correlation (1950-2014) between SST and 0-400
Meter Averaged Salinity (50-60°N, 50-10°W)
Linear Trend in Annual Sea Surface Temperature (2005-2014)
There is some recent evidence that overall Atlantic hurricane
activity may have increased since in the 1950s and 60s in
association with increasing sea surface temperatures…
Source: Kerry Emanuel, J. Climate (2007).
PDI is proportional to the time
integral of the cube of the surface
wind speeds accumulated across all
storms over their entire life cycles.
Late 21st Century projections: increased vertical wind
shear may lead to fewer Atlantic hurricanes
Average of 18 models, Jun-Nov
“storm-friendly”
Source: Vecchi and Soden, Geophys. Res. Lett., (2007)
“storm-hostile”