Transcript Ch12: Tropical Storms and Hurricanes

How do the hurricanes amplify?
Review of last lecture
• Tropical cyclone genesis: Western Pacific has the
highest averaged number per year
• 6 necessary conditions for tropical cyclone
genesis
• 4 stages of tropical cyclone genesis
• Tropical cyclone tracks
• Tropical cyclone intensity scale. Category 1:
74mph, category 5: 155mph
• Hurricane names: alphabetically, 6 lists in rotation
• Trends and variability in tropical cyclone activity
Video: Hurricane Structure
http://www.youtube.com/watch?v=OEPZ
OC6YHUc
Horizontal Structure of tropical cyclones
• Total diameter: about 600km
• Lifetime: up to a week or more
• Make up: many thunderstorms
arranged in pinwheel formation
• Three components:
1. Central eye - clear skies, light
winds (25 km diameter)
2. Eye wall - strongest winds
(can be 200 mph), max precip. (up
to 2500 mm/day)
3. Spiral rainbands
• Cylonic inflow, anticyclonic
outflow. Outflow creates cirrus
shield that often obscures
pinwheel structure
Vertical Structure: Wind flow
H
L
Vertical Structure:
Heating, temperature, pressure and wind
H
L
• Warm core fueled by thermal
energy - core
warmer than
outside at upper
levels
• Maximum rainfall
occur in the region
of eye wall
• Minimum surface
pressure occurs in
the region of central
eye
• Maximum winds
occur in the region
of eye wall
Eye wall replacement
• A shrinking eye indicates
storm intensification.
• Some intense hurricanes
develop double eye walls,
as rain bands contract and
intensify.
• Eye wall replacement
leads to weakening of the
hurricane winds, followed
by renewed strengthening.
Vertical Structure: Feedbacks
Sea surface temperature
1. Convergence-Convection (CISK): positive
2. Surface flux-Convection (WISHE): positive
3. Air-sea interaction: negative
Hurricane Landfall
Video: Landfall of Hurricane Sandy
http://www.youtube.com/watch?v=YeutC
1WN6dc
Tropical cyclone Destruction and Fatalities
Destruction caused by:
• Hurricane-scale winds (>74 mph)
• Rainfall (10 in/day)
• Storm surge (winds blowing coast-ward + lower atmosphere pressure)
• Fine-scale Tornadoes
Destruction most intense on right side of cyclone (wind + storm speed)
Hurricane-spawned tornadoes
• More than half of the landfall
hurricanes produce at least one
tornado
• Hurricane Buelah (1967) produced
141 tornadoes
• Most likely occur in the right-front
quadrant
• Generally less intense than those
that occur in the great plains
Hurricane Destruction: Storm Surges
• The storm surge is a rise in
water level induced by a
hurricane. They occur as water
piles due to heavy winds and low
atmospheric pressure and
increase with storm intensity.
• High surf can occur atop the
storm surge, increasing damage.
• Winds and storm surge are
typically most intense in the right
front quadrant of the storm
where wind speeds combine with
the speed of the storm’s
movement to create the area of
highest potential impact.
Hurricane Forecasts and Advisories
•
The National Hurricane Center is
responsible for predicting and
tracking Atlantic and east Pacific
hurricanes.
•
Data are gathered through satellite
observations, surface
observations, and aircraft using
dropsondes (packaging
containing temperature, pressure,
and moisture sensors).
•
Statistical, dynamic, and hybrid
computer models running on
supercomputers assist in
forecasting track position and
storm intensity.
•
Future positions are given along
six-hour trajectories with accuracy
decreasing as lead time increases.
By Tim Marchok of NOAA/GFDL
Hurricane Watches and
Warnings
• A hurricane watch is issued if
an approaching hurricane is
predicted to reach land in
more than 24 hours.
• If the time frame is less, a
hurricane warning is given.
• Tropical storm watches and
tropical storm warnings are
issued with the same
anticipated lead time.
• The erratic nature these storm
systems leads to difficulties in
exact prediction, warning, and
evacuation.
Tropical cyclone forecast skill: Track
Tropical cyclone forecast skill: Intensity
Summary
• Tropical cyclone structure: 3 major components,
rotation direction of inflow and outflow, location of
maximum wind and rainfall, 3 feedbacks
• Tropical cyclone destruction: 4 reasons? Which
side has the most intense destruction?
• Tropical cyclone forecast: track and intensity
Currently which skill is better?