Q2 - International Workshop on Wave Hindcasting and Forecasting

Diagnosing the Large Swell Event Associated with
the Extratropical Transition of Hurricane Florence
Mark Willis
National Hurricane Center
Tropical Analysis and Forecast Branch (TAFB)
Thanks to: Jack Beven, Robbie Berg, John
Cangiolosi, and Jamie Rhome.
TAFB Area of Responsibility
MOTIVATION
• PROTECT LIFE AND PROPERTY – At least two
drownings, hundreds of ocean rescues, erosion, and
flooding resulted from this swell event.
• 22% of all tropical cyclone related deaths are
offshore or surf related (2nd only to inland flooding),
Rappaport (2000).
• Improve public misperceptions of swell events from
tropical cyclones – the category and type of storm
don’t matter!
• Wave model guidance did not represent the peak of
the swell event very well. Why?
• Improve NWS/NCEP marine forecast products.
METHODOLOGY
• A detailed case study was performed to understand
the social and scientific challenges associated with
the large swell event from Hurricane Florence.
• Gain an understanding for the meteorology in
hindsight – what atmospheric patterns made the
waves so big?
• Compared strengths and weaknesses in the
available wave model guidance at TAFB – NWW3,
NAH WW3, WNA WW3, FNMOC WW3.
• Located problems in the GFDL and GFS wind forcing
that led to problems in the NAH and WNA models.
• Compared swell of Florence (Cat 1) to Luis (Cat 4).
CONCLUSIONS
•
•
•
•
•
•
This uniquely large swell event was due to: large storm from
origin, ET, interaction with strong Canadian high pressure that
built south.
NAH and WNA WW3’s low with height and period offshore
Florida on 14 Sept due to problems in the GFDL and GFS wind
forcing on 13 Sept.
WW3’s OVERestimated the heights and low with the periods off
Cape Hatteras for the same reason.
As marine forecasters, we always need to get a handle on the
wind progs first, then waves.
NAH isn’t always better than WNA for tropical cyclones –
especially ones going through ET.
Further outreach is needed to inform the public of potential
indirect dangers of tropical cyclones (Swells and Surf!), and the
misperceptions of the Saffir Simpson scale.
Hurricane Florence ( Sept 2006)
65
60
18
19
Hurricane Florence
3 - 12 September 2006
17
Hurricane
Tropical Storm
Tropical Dep.
55
Extratropical
Subtr. Storm
50
15
16
14
Subtr. Dep.
Low / Wave
45
00 UTC Pos/Date
12 UTC Position
40
NE swell peaking in Florida after
NHC advisories ceased
13
PPP Min. press (mb)
12
35
974 mb
11
30
10
25
9
20
8
7
6
15
5
4
10
-90
-85
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
Hurricane Florence ( Sept 2006)
THE METEOROLOGY
• Large storm from
origin.
• Strong high pressure
over Canada built
south 11-13 Sept.
• This allowed
significant NE fetch to
build SW towards
Florida.
• Led to peak of swell
in FL as Florence
seemingly was not a
threat and moving out
to sea.
NWS/NCEP Unified Surface Analysis 12Z 11 Sept 2006
Wave Model Verification
Swell Peaking in Florida when
Florence was moving out to sea and
no longer tropical – dangerous!
Wave heights offshore Central Florida
Wave Model Verification
Wave periods offshore Central Florida
Wave Model Verification
Wave heights offshore Cape Hatteras
Wave Model Verification
Wave periods offshore Cape Hatteras
Why were the NAH and WNA
WW3’s off? – The wind forcing!
GFDL Winds (used in NAH WW3) vs. Observations
Why were the NAH and WNA
WW3’s off? – The wind!
GFS better than GFDL with developing
frontal structure N/NE of center, worse
with high winds near core.
GFS Winds (used in WNA WW3) vs. Observations
Florence (Cat 1, 2006) vs. Luis (Cat 4, 1995)
Luis
Florence
Saffir-Simpson Scale
* Denotes major hurricane
Category
Category11
•• Storm
Storm surge:
surge: 4-5
4-5 ftft above
above normal.
normal. Some
Some coastal
coastal road
road flooding
flooding and
and minor
minor pier
pier damage.
damage.
(64-82 kt)
(64-82 kt)
•• Wind
Wind Damage:
Damage: Primarily
Primarily to
to unanchored
unanchored mobile
mobile homes,
homes, shrubbery,
shrubbery, and
and trees.
trees. Some
Some damage
damage to
to poorly
poorly
constructed
signs.
Scattered
downed
power
lines
and
power
outages.
constructed signs. Scattered downed power lines and power outages.
Winds:
mph
Winds:74-95
74-95 mph
Pres:
mb
Pres:>>980
980 mb
29.94 "Hg
29.94 "Hg
Category
Category22
Winds:
mph
Winds:96-110
96-110 mph
(83-95 kt)
(83-95 kt)
Pres:
mb
Pres:965-979
965-979 mb
28.50-28.91 "Hg
•• Storm
6-8 feet
feet above
above normal.
normal. Coastal
Coastal and
and low-lying
low-lying escape
escape routes
routes flood
flood 2-4
2-4 hours
hours before
before arrival
arrival of
of the
the
Storm surge:
surge: 6-8
center.
center.
•• Wind
Wind Damage:
Damage: Some
Some roofing
roofing material,
material, doors,
doors, and
and window
window of
of buildings.
buildings. Considerable
Considerable damage
damage to
to shrubbery
shrubbery and
and
trees
trees with
with some
some trees
trees blown
blown down.
down. Considerable
Considerable damage
damage to
to mobile
mobile homes,
homes, poorly
poorly constructed
constructed signs,
signs, and
and piers.
piers.
Small
Small craft
craft in
in unprotected
unprotected anchorages
anchorages break
break moorings.
moorings. downed
downed power
power lines
lines and
and power
power outages.
outages.
28.50-28.91 "Hg
Category
Category3*
3*
•• Storm
9-12 ftft above
above normal.
normal. Low-lying
Low-lying escape
escape routes
routes cut
cut by
by rising
rising water
water 3-5
3-5 hours
hours before
before arrival
arrival of
of the
the
Storm surge:
surge: 9-12
center
of
the
hurricane.
Flooding
near
coast
destroys
smaller
structures
with
larger
structures
damaged
by
center of the hurricane. Flooding near coast destroys smaller structures with larger structures damaged by
battering
battering from
from floating
floating debris.
debris. Terrain
Terrain lower
lower than
than 55 ftft above
above mean
mean sea
sea level
level may
may be
be flooded
flooded inland
inland 88 miles
miles or
or
more.
more.
Pres
mb
Pres: 945-964
: 945-964 mb
27.91-28.47 "Hg
27.91-28.47 "Hg
•• Wind
Some structural
structural damage
damage to
to small
small residences
residences and
and utility
utility buildings
buildings with
with minor
minor amount
amount of
of curtain
curtain
Wind Damage:
Damage: Some
wall
wall failures.
failures. Foliage
Foliage blown
blown off
off trees
trees and
and large
large trees
trees blown
blown down.
down. Mobile
Mobile homes
homes and
and poorly
poorly constructed
constructed signs
signs
destroyed.
destroyed. Numerous
Numerous downed
downed power
power lines
lines and
and power
power outages.
outages.
• •Storm
13-18ftftabove
abovenormal.
normal.Low-lying
Low-lyingescape
escaperoutes
routesmay
maybe
becut
cutby
byrising
risingwater
water3-5
3-5hours
hoursbefore
before
Stormsurge:
surge:13-18
arrival
of
the
center
of
the
hurricane.
Major
damage
to
lower
floors
of
structures
near
the
shore.
arrival of the center of the hurricane. Major damage to lower floors of structures near the shore.Terrain
Terrainlower
lower
than
than10
10ftftabove
abovesea
sealevel
levelmay
maybe
beflooded
floodedrequiring
requiringmassive
massiveevacuation
evacuationofofresidential
residentialareas
areasas
asfar
farinland
inlandas
as66
miles.
miles.
Winds:
mph
Winds:111-130
111-130 mph
(96-113 kt)
(96-113 kt)
Category
Category4*
4*
Winds:
mph
Winds:131-155
131-155 mph
(114-135 kt)
(114-135 kt)
Pres:
mb
Pres:920-944
920-944 mb
27.17-27.88 "Hg
27.17-27.88 "Hg
Category
Category5*
5*
Winds:
mph
Winds:>>155
155 mph
(> 135 kt)
(> 135 kt)
Pres:
mb
Pres:<<920
920 mb
<27.16 "Hg
<27.16 "Hg
• •Wind
Extensivecurtain
curtainwall
wallfailures
failureswith
withsome
somecomplete
completeroof
rooffailures
failureson
onsmall
smallresidences.
residences.Shrubs,
Shrubs,
WindDamage:
Damage:Extensive
trees,
and
all
signs
are
blown
down.
Complete
destruction
of
mobile
homes.
Extensive
damage
trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damagetotodoors
doorsand
and
windows.
windows. Widespread
Widespreaddamage
damagetotopower
powerlines
linesand
andpower
poweroutages.
outages.
•• Storm
18 ftft above
above normal.
normal. Low-lying
Low-lying escape
escape routes
routes are
are cut
cut by
by rising
rising water
water 3-5
3-5 hours
hours before
before arrival
arrival of
of
Storm surge:
surge: >> 18
the
center
of
the
hurricane.
Major
damage
to
lower
floors
of
all
structures
located
less
than
15
ft
above
the center of the hurricane. Major damage to lower floors of all structures located less than 15 ft above sea
sea level
level
and
and within
within 500
500 yards
yards of
of the
the shoreline.
shoreline.
•• Wind
Complete roof
roof failure
failure on
on many
many residences/industrial
residences/industrial buildings.
buildings. Some
Some complete
complete building
building failures
failures
Wind Damage:
Damage: Complete
with
with small
small utility
utility buildings
buildings blown
blown over
over or
or away.
away. All
All shrubs,
shrubs, trees,
trees, and
and signs
signs blown
blown down.
down. Complete
Complete destruction
destruction of
of
mobile
mobile homes.
homes. Severe
Severe and
and extensive
extensive window
window and
and door
door damage.
damage. Extensive
Extensive damage
damage to
to power
power lines
lines and
and
widespread
widespread power
power outages.
outages.
Florence (Cat 1, 2006) vs. Luis (Cat 4, 1995)
FLORENCE MAX 70 KT
OR LUIS MAX 120 KT ?
Which storm created the largest swell offshore Florida?
And the winner is…TIE! Both swell
events peaked around 14’ at 16s.
Not unusual for Oahu, but very
unusual for Florida.
Saffir Simpson Scale not
valid for swell events.
Outreach needed to teach
the public this.
Swell photos
Thank You.
Questions,
Comments?