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Hurricane Winds

Hurricane Winds. Mark Powell NOAA-AOML Hurricane Research Division. M. POWELL HURRICANE IMPACTS 2012. Measuring. A VARIETY OF SENSORS EXAMINE THE STORM ’ S WIND FIELD. M. POWELL HURRICANE IMPACTS 2012. Wind Field. Peak wind determines intensity Extent of damaging winds: radii

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Hurricane Winds

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  1. Hurricane Winds • Mark Powell NOAA-AOML Hurricane Research Division M. POWELL HURRICANE IMPACTS 2012

  2. Measuring A VARIETY OF SENSORS EXAMINE THE STORM’S WIND FIELD M. POWELL HURRICANE IMPACTS 2012

  3. Wind Field • Peak wind determines intensity • Extent of damaging winds: radii • Projection of tropical storm winds relates to evacuation KATRINA 24 HOURS BEFORE LANDFALL M. POWELL HURRICANE IMPACTS 2012

  4. Landfall KATRINA 4 AM CDT • Moving 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 M. POWELL HURRICANE IMPACTS 2012

  5. Landfall KATRINA 7 AM CDT • Pressure begins to rise • Pressure gradient weakens • Peak winds begin to decrease • wind field expands: conservation of angular momentum M. POWELL HURRICANE IMPACTS 2012

  6. Landfall Winds KATRINA 7 AM CDT • Structures 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 M. POWELL HURRICANE IMPACTS 2012

  7. Post Landfall KATRINA 10AM CDT • Pressure continues rising • Pressure gradient continues weakening • Enhanced friction diminishes the wind field M. POWELL HURRICANE IMPACTS 2012

  8. Storm Decay ANDREW 6 HOURS AFTER LANDFALL • 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 M. POWELL HURRICANE IMPACTS 2012

  9. 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 MISSILES LOFTED DURING HURRICANE INIKI ON LIHUE (BRUCE ASATO, HONOLULU ADVERTISER) HURRICANE MARILYN 1995 HILLTOP DAMAGE ON ST. THOMAS M. POWELL HURRICANE IMPACTS 2012

  10. Hurricane Tornadoes • Mostly in outer bands • Mostly front right • Weaker than great plains types • Difficult to detect • Short life times, move quickly • Additional damage: microbursts M. POWELL HURRICANE IMPACTS 2012

  11. Hurricane Andrew 1992 M. POWELL HURRICANE IMPACTS 2012

  12. Wind Damage • Force 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

  13. 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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