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
Projection of tropical storm
winds relates to evacuation
KATRINA 24 HOURS BEFORE
LANDFALL
M. POWELL HURRICANE IMPACTS 2012
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
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
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
Post Landfall
KATRINA 10AM CDT
Pressure continues rising
Pressure gradient
continues weakening
Enhanced friction
diminishes the wind field
M. POWELL HURRICANE IMPACTS 2012
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
Wind Damage
Turbulence lofts missiles
Complex terrain
Local hilltops can
double the wind
MISSILES LOFTED DURING HURRICANE INIKI ON LIHUE
(BRUCE ASATO, HONOLULU ADVERTISER)
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
M. POWELL HURRICANE IMPACTS 2012
Hurricane
Tornadoe
s
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
Hurricane Andrew 1992
M. POWELL HURRICANE IMPACTS 2012
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
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