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Required Characteristics for a Tropical Cyclone:
- Warm core
- Low pressure
- develops over tropical or sub-tropical waters
- Organized surface circulation
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3 Types of Tropical Cyclone and their wind speeds:
- Tropical Depression (<39 mph)
- Tropical Storm (39-73 mph)
- Hurricane (74+)
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What kind of core does an extratropical cyclone have?
Cold Core
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What are extratropical cyclone associated with?
- Cold fronts
- Warm fronts and
- Occluded fronts
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Characteristics of warm core systems?
- Strongest winds at or near the surface
- They develop using the heat from the underlying warm surface and using convection to elevate it.
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Required characteristics for a Hurricane:
- Pre-existing disturbance (Easterly wave)
- Warm water
- Atmospheric instability
- Sufficient low-level cyclonic (positive) vorticity
- Abundant mid-level moisture
- Low vertical wind shear
- Divergence in the upper atmosphere
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Saffir-Simpson Wind Scale categories for Hurricane Intensity (based on expected damage to structures):
- 1 74-95 mph
- 2 96-110
- 3 111-130
- 4 131-155
- 5 >156
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Area of minimum central pressure
The Eye
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Area of strongest winds:
Eyewall
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What is the RMax?
- Distance from the storm center to the strongest winds is called the radius to maximum winds (Rmax).
- Here and in feeder bands, air is moving toward the center and upward into the
- high level clouds.
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What are Feeder Bands?
Bands of heavy rain, convection and strong gusty winds that spiral in toward the center of a hurricane.
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What are "damage functions"?
Mathematical equations that describe the interaction between buildings and their contents and the local intensity to which they are exposed. They are validated from damage surveys after events and from billions of dollars of claims data.
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Greater number of simulated events correlates how to actual historical events?
Very closely
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Useful frequency distribution for the tail
Negative Binomial
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Minor differences in the tail lead to:
Larger differences in the return period of extreme, multiple season events
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Landfall happens when:
The eye crosses the land.
A storm can have multiple landfalls.
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Bypassing storm:
Doesn't make landfall but passes sufficiently close to cause damaging winds over land.
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US Landfall Segments happen every:
50 Nautical Miles
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For each scenario year, the model generates the number of hurricanes that occur that year, and for each simulated hurricane, parameter values are assigned. These parameters include:
- Landfall location
- Minimum central pressure
- Radius of maximum winds
- Forward speed
- Track angle at landfall
- Track direction at each time step
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Smoothing
Used for modeling hurricane landfalls in the US, it reduces the effect of scarcity of historical data for hurricanes.
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Primary determinant of intensity?
- Central Pressure
- Modeled using Weibull distributions.
- Wind speed measurements are not reliable.
AIR used Central Pressure, NOT wind speeds.
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Distance from the storm's center, or eye, to where the strongest winds are found in the eyewall:
RMax (Radius of Maximum Winds)
- Varies with Central Pressure and Latitude
- Smaller the RMax, usually the more intense the storm. Also, storms typically become larger at northern latitudes.
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Measured using mean and standard deviation from which a log-normal distribution is built:
Forward Speed
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Sizes of catalogs for Hurricane models
10K, 50K and 100K
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WSST
- Warm Sea Surface Temperature catalog
- Contains all the events in the standard catalog PLUS additional events by segment and intensity to reflect the impact of warm sea surface temperatures.
- Conditioned on only those seasons in which the Atlantic Ocean has been warmer than average.
- 10K, 50K and 100K catalogs for the US and entire Basin.
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Hurricanes spin counter clockwise in the Northern Hemisphere. Hurricane winds and forward motion produce stronger winds on the right hand side of the storm. This is called:
Storm Asymmetry
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Wind Velocity Profiles:
- Higher winds at higher elevations.
- Slower winds at ground level because of surface friction.
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Significant risk to property in Southeast Asia:
Flooding
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