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