hurricane winds mark powell noaa-aoml hurricane research division m. powell hurricane impacts 2012
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Hurricane WindsMark Powell NOAA-AOML Hurricane Research Division
M. POWELL HURRICANE IMPACTS 2012
MeasuringA VARIETY OF
SENSORS EXAMINE THE STORM’S WIND
FIELD
M. POWELL HURRICANE IMPACTS 2012
Wind FieldPeak wind determines intensityExtent of damaging winds: radiiProjection of tropical storm winds relates to evacuation
KATRINA 24 HOURS BEFORE LANDFALL
M. POWELL HURRICANE IMPACTS 2012
LandfallMoving northward closer to land, storms:
Encounter cooler water on the continental shelf
Interact with shear from approaching cold fronts
Receive inflow of cooler, drier air flowing offshore
KATRINA 4 AM CDT
M. POWELL HURRICANE IMPACTS 2012
LandfallPressure begins to rise
Pressure gradient weakens
Peak winds begin to decrease
wind field expands: conservation of angular momentum
KATRINA 7 AM CDT
M. POWELL HURRICANE IMPACTS 2012
Landfall WindsStructures and vegetation (roughness) slow down the wind
Frictional Inflow increases
Convergence zones can increase
Gustiness (turbulence) increases
Large wind differences between marine, open, suburban areas
KATRINA 7 AM CDT
M. POWELL HURRICANE IMPACTS 2012
Post LandfallPressure continues rising
Pressure gradient continues weakening
Enhanced friction diminishes the wind field
KATRINA 10AM CDT
M. POWELL HURRICANE IMPACTS 2012
Storm Decay
Cooler, drier air over land: less fuel for the heat engine
Stronger storms decay faster
By 6 h after landfall, Andrew reduced from 140 kts to 95 kts
ANDREW 6 HOURS AFTER LANDFALL
M. POWELL HURRICANE IMPACTS 2012
Wind Damage
Turbulence lofts missiles
Complex terrain
Local hilltops can double the wind
Valleys and gorges can funnel the wind
Wind tunnel modeling and flow models can help identify risk areas
HURRICANE MARILYN 1995 HILLTOP DAMAGE ON ST. THOMAS
MISSILES LOFTED DURING HURRICANE INIKI ON LIHUE (BRUCE ASATO, HONOLULU ADVERTISER)
M. POWELL HURRICANE IMPACTS 2012
Hurricane TornadoesMostly in outer bandsMostly front rightWeaker than great plains typesDifficult to detectShort life times, move quicklyAdditional damage: microbursts
M. POWELL HURRICANE IMPACTS 2012
Hurricane Andrew 1992
M. POWELL HURRICANE IMPACTS 2012
Wind DamageForce goes with wind2
Turbulence: Cycling between gusts and lulls causes fatigue
Roof suction pressures related more to turbulent wind structure than peak wind
Wind direction: houses experiencing winds from many directions compared to one general direction (eye vs eyewall)
Upstream terrain
M. POWELL HURRICANE IMPACTS 2012
Eyewall Damage: Hurricane Andrew
Importance of construction details
Strong building code
Code enforcement and product approval
PHOTO: POWELL, NARANJA LAKES AFTER HURRICANE ANDREW
M. POWELL HURRICANE IMPACTS 2012
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