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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E954
ABSTRACT: Hurricane Lane (2018) was an impactful event for the Hawaiian Islands and provided
a textbook example of the compounding hazards that can be produced from a single storm.
Over a 4-day period, the island of Hawaiʻi received an island-wide average of 424 mm (17 in.) of
rainfall, with a 4-day single-station maximum of 1,444 mm (57 in.), making Hurricane Lane the
wettest tropical cyclone ever recorded in Hawaiʻi (based on all available quantitative records).
Simultaneously, fires on the islands of nearby Maui and Oʻahu burned 1,043 ha (2,577 ac) and
162 ha (400 ac), respectively. Land-use characteristics and antecedent moisture conditions exac-
erbated fire hazard, and both fire and rain severity were influenced by the storm environment and
local topographical features. Broadscale subsidence around the storm periphery and downslope
winds resulted in dry and windy conditions conducive to fire, while in a different region of the same
storm, preexisting convection, incredibly moist atmospheric conditions, and upslope flow brought
intense, long-duration rainfall. The simultaneous occurrence of rain-driven flooding and landslides,
high-intensity winds, and multiple fires complicated emergency response. The compounding
nature of the hazards produced during the Hurricane Lane event highlights the need to improve
anticipation of complex feedback mechanisms among climate- and weather-related phenomena.
https://doi.org/10.1175/BAMS-D-19-0104.1
Corresponding author: Alison D. Nugent, anugent@hawaii.edu
In final form 27 January 2020
©2020 American Meteorological Society
For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy.
Article
Fire and Rain
The Legacy of Hurricane Lane in Hawaiʻi
Alison D. Nugent, Ryan J. Longman, Clay Trauernicht,
Matthew P. Lucas, Henry F. Diaz, and Thomas W. Giambelluca
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E955
AFFILIATIONS: Nugent—Department of Atmospheric Sciences, University of Hawaiʻi at Mānoa, Hono-
lulu, Hawaiʻi; Longman—East West Center, Honolulu, Hawaiʻi; Trauernicht—Department of Natural
Resources and Environmental Management, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi; Lucas
and Diaz—Department of Geography and Environment, University of Hawaiʻi at Mānoa, Honolulu,
Hawaiʻi; Giambelluca—Water Resources Research Center and Department of Geography and Environ-
ment, University of Hawaiʻi at Mānoa, Honolulu, Hawaiʻi
Severe tropical cyclones are arguably the most destructive storms on Earth. Commonly
referred to as “hurricanes” in the North Atlantic and eastern North Pacic, “typhoons” in
the western North Pacic, and “cyclones” elsewhere, these storms pose multiple threats
to the people and property that lie in their paths. Research on fatalities from Atlantic tropical
cyclones has shown that the most lethal aspects of these storms are (beginning from the most
severe threat) storm surge, rain, wind, and coastal and oshore hazards such as waves and
rip currents (Rappaport 2014). Although the specic threats vary from storm to storm and
place to place, single storm events pose multifaceted and potentially cumulative hazards.
The vulnerability of a population in any given location to the impacts of tropical cyclone
hazards is determined by and mediated by a multitude of interacting factors. Biophysical as-
pects include distance inland from the coast, terrain slope, coastal ecosystem integrity, and
land surface cover. Socioeconomic factors include infrastructure quality, the availability of
early warning systems, and capacity for evacuation and emergency response. The combina-
tion of biophysical and socioeconomic factors influences the severity of storm impacts in any
given place (Turner et al. 1996).
In Hawaiʻi, landfall by hurricanes is relatively rare due to persistent vertical wind shear
over the islands. The earliest report of a major hurricane causing severe damage in Hawaiʻi
dates back to 1871 (Businger et al. 2018) and since 1950, only five hurricanes (Nina in 1957,
Dot in 1959, Iwa in 1982, Estelle in 1986, and Iniki in 1992) have caused serious damage to
the main islands of Hawaiʻi (Smith et al. 2012). Hurricane Iniki (1992) was the strongest and
most destructive of these storms, with sustained 145-mph (1 mph ≈ 0.45 m s−1) winds just prior
to landfall, that caused an estimated US$1.8 billion in property damage and six fatalities
(Brown et al. 1993). When hurricanes do occur near Hawaiʻi, the geography of the islands can
exacerbate the hazards. The nearly 1,200 km (746 mi) of coastline makes much of the state
susceptible to coastal flooding, and the mountainous topography can enhance atmospheric
lifting and subsequent high-intensity rainfall, as well as intensifying wind speeds. In addi-
tion, the steep mountainous terrain can enhance flash flooding and trigger landslide events.
The 2018 Northern Hemisphere hurricane season was especially active, with a combined
total of 66 storms occurring in the Atlantic and Pacific basins. The Atlantic basin had 15 named
storms, including 8 hurricanes and 2 major hurricanes (>111-mph sustained winds, equivalent to
category 3, 4, or 5 on the Saffir–Simpson scale; NOAA/NHC 2019), while the central and eastern
Pacific had 22 total named storms, including 13 hurricanes and 10 major hurr icanes (NOAA/CPHC
2019). Activity from these storms set a new record for accumulated cyclone energy, a measure of
total wind energy, in the northeast Pacific since 1971 when the record began (Klotzbach and Bell
2018). Anomalously warm sea surface temperatures (SSTs) were found across the world (NOAA/
NCEI 2019), and the global ocean surface heat content (upper 700 m) for July–September 2018
was the highest since records began in 1955 for both the Atlantic and Pacific basins (NOAA/NCEI
2018). Increased ocean heat is potentially explained by El Niño–Southern Oscillation, which
developed from a neutral phase over the summer of 2018 leading to El Niño (warm) conditions
that emerged in September and persisted through the following winter.
Around the Hawaiian Islands, SSTs were just above 27°C throughout August 2018, slightly
higher than the 26.7°C seasonal average in the region (Coral Reef Watch 2019), and over a
2-month period (8 Augu st–4 October) five hurricanes tracked within 445 km (275 mi) of the island
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E956
chain. Hurricanes Hector (category 4), Lane (category 5), Norman (category 4), Olivia (category
4), and Walaka (category 5) all entered Hawaiian waters, causing varying degrees of damage
in the islands. Of these storms, only Olivia made landfall on the main Hawaiian Islands, after
being downgraded to a tropical storm. Hurricane Walaka (ranked the second strongest tropi-
cal cyclone ever recorded in the central Pacific) passed near to and essentially destroyed East
Island, one of the unpopulated northwestern Hawaiian Islands (NOAA/CPHC 2018). Hurricane
Lane (hereafter, Lane) was by far the costliest storm of the 2018 hurricane season in Hawaiʻi.
Despite never making landfall, Lane caused considerable damage and disruptions across the
state, including severe flooding on the island of Hawaiʻi and multiple fires on the islands of
Maui and Oʻahu. In fact, the damages from the floods and fires were so severe that it prompted
the U.S. government to issue a major disaster declaration for this event (FEMA 2018).
Hurricane–fire interactions have been documented in the literature (Myers and van Lear
1998; Liu et al. 2008; Platt et al. 2002; Christopher et al. 2009). The general hypothesis is that
fire hazard can increase after an intense hurricane due to greater fuel loads from downed
woody debris and litter, and lower fuel moistures due to increased insolation and higher wind
speed under an open canopy (Myers and van Lear 1998). Liu et al. (2008) showed that on the
Gulf of Mexico coast, the highest-intensity fires tended to occur within years or decades after
a catastrophic hurricane strike. However, real-time interactions of hurricane and concurrent
fire events are very rarely reported. The only two we have found documented are Subtropical
Storm Andrea (2007), which exacerbated fires already burning in the Okefenokee National
Wildlife Refuge across Florida and Georgia (Christopher et al. 2009; Barbero et al. 2015; FDEM
2011), and a recently reported connection between storm-force winds from Hurricane Ophelia
(2017) and wildfires in Portugal (Fernandes 2018). While heavy rain is a familiar feature of
tropical storms, the strong convection near the storm center is also associated with, or perhaps
compensated by, descending air around the storm’s periphery (Fett 1964). This subsiding air
is warm and dry, and together with intense storm-driven winds, we hypothesize this could
increase the risk of fire hazard in the periphery of the hurricane, especially if preexisting
conditions predisposed the area to fire. The potential for compounding hazards warrants
further exploration, and to date, the authors are not aware of any work documenting the
simultaneous occurrence of both heavy rainfall and fire during a hurricane event. The Lane
event therefore provides a compelling case study of how atmospheric conditions associated
with hurricanes can simultaneously contribute to record rainfall and increased fire risk.
The primary objective of this study is to present a detailed analysis of the multiple haz-
ards associated with the passage of Lane in the Hawaiian region over the 4-day period of
22–25 August 2018 (Fig. 1) and to determine how simultaneous fire and rain impacts from a
hurricane can both be possible. First, we provide a synopsis of the storm. Next, we draw on
several data sources to identify and characterize how environmental conditions contributed
to intense rainfall and severe flooding on the island of Hawaiʻi and to multiple wildfires that
occurred on the islands of Maui and Oʻahu during the storm passage. Finally, we discuss
land use changes that are likely to impact fire risk, terrain interactions that can exacerbate
hazards associated with wind and rain, and specific features of the hurricane environment.
Datasets and methods
A combination of surface observations were used to investigate the storm environment with
a focus on precipitation and re weather.
Rainfall data. Daily precipitation data were used to characterize the Lane event and the months
leading up to it. These data were obtained from several national online data repositories in-
cluding the National Center for Environmental Information (NCEI; www.ncei.noaa.gov/) and the
Hydrometeorological Automated Data System (HADS; https://hads.ncep.noaa.gov/) along with
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E957
additional data from various local networks. A 25-yr (1990–2014) time series of daily rainfall
maps on a 250-m grid were utilized to characterize past rainfall events [see Longman et al.
(2018) for a complete description of local networks and data sources in Hawaiʻi]. In total, 156
rainfall stations with continuous data over the 4-day event were identified across the state
(Fig. 2). Mean monthly rainfall climatologies were obtained from the Rainfall Atlas of Hawai‘i
(Giambelluca et al. 2013).
Meteorological stations. The atmospheric conditions contemporaneous with wildfires on
Maui and Oʻahu during the Lane event are examined using hourly and daily observations of
“fire weather” variables based on the National Weather Service (NWS) red flag warning criteria
for Hawaiʻi (NWS/HFO 2018a). The NWS tracks the daily Keetch–Byram drought index (KBDI),
hourly wind speed, and relative humidity (RH) at the Daniel K. Inouye International Airport
(PHNL) in Honolulu and uses the thresholds indicated in Fig. 3 to declare red flag warnings for
high fire danger when all thresholds are crossed and maintained for at least 2 h. KBDI is cal-
culated from mean annual rainfall, daily rainfall, and temperature, such that the KBDI value
indicates the quantity of rain (mm) necessary to saturate the soil. Larger KBDI values indicate
more severe drought conditions, and over time the value of KBDI steadily increases when no rain
is received. As a daily index, KBDI captures short-term fluctuations in moisture availability and
performs well for fire prediction in tropical and subtropical climates such as Hawaiʻi (Dolling
et al. 2005; Brolley et al. 2007). In Fig. 3, KBDI was derived from NWS calculations at PHNL;
however, RH and wind data were obtained from Kapalua Airport (PHJH) in Lahaina, Maui, and
Fig. 1. The background image shows a visible image from GOES-15 of Hurricane Lane at 2300 UTC
22 Aug 2018 when its eye was centered at ~15°31΄00�N, 156°11΄00�W near the Hawaiian Islands
in the central Pacific . The white dashed line indicates the best track of Lane (Knapp et al. 2010),
labeled with dates and times (UTC), and the color of the hurricane symbol indicates the strength
of winds in the storm.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E958
Kalaeloa Airport (PHJR) on Oʻahu, the closest high-quality weather stations to the fires. Drought
status was also characterized using the National Drought Monitor (Svoboda et al. 2002) condi-
tions at the fire locations. Finally, the Hilo radiosonde sounding (PHTO) was utilized for time
series of the vertical profile of atmospheric conditions.
Fire extent and land cover. The areas burned by fires on Maui and Oʻahu were mapped in
Google Earth Engine using Sentinel- satellite images captured within 2 months following the
fires (Drusch et al. 2012). Land cover on the islands and within the burned areas was obtained
from a 2.4-m resolution NOAA Coastal Change Analysis Program (C-CAP) land cover product
(Klemas et al. 1993), last updated for Maui in 2010 and for Oʻahu in 2011.
Rainfall mapping. Following methods similar to those used by Longman et al. (2019), daily
precipitation maps were created for the island of Hawaiʻi using an inverse distance weighting
(IDW) approach combined with climatologically aided interpolation (Willmott and Robeson
1995). For each day, anomalies were calculated as the ratio of station daily rainfall to mean
daily rainfall retrieved from the Rainfall Atlas of Hawaiʻi at the station location (Giambelluca
et al. 2013). Station anomalies were then interpolated to a 250-m grid for each island.
Finally, the gridded daily anomalies were multiplied by the gridded daily mean to produce a
daily rainfall map. The 4-day Lane event rainfall was calculated as the sum of the four-daily
(midnight to midnight local time) rainfall grids within 22–25 August 2018 time period. Finally,
Fig. 2. Map highlighting the locations impacted by heavy rainfall and fire in the Hawaiian Islands.
Circular dots indicate the location of rain gauges used for estimating precipitation from Hurricane
Lane, and the 4-day accumulated rainfall totals (mm) from 22 to 25 August 2018. Also included
are the locations of the wildfires on Maui and Oʻahu, with their burned areas denoted in red, and
the locations of the Kalaeloa Airport (PHJR) and Lahaina, Maui (PHJH), weather stations used for
analysis denoted with purple triangles.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E959
4-day Lane rainfall was compared to rainfall for all 4-day periods in the 25-yr daily gridded
rainfall time series.
Our methods of rainfall mapping during the Lane event differ from those of Longman et al.
(2019) in that we use all available stations (as opposed to the closest five) in the interpola-
tion of anomalies and a weighting parameter of 1 (as opposed to 1.5). These parameters were
updated as a result of optimization conducted during this present analysis and are specific
to the island of Hawaiʻi. To enable comparison between Lane and past events, we reanalyzed
the entire 25-yr (1990–2014) set of daily rainfall maps from Longman et al. (2019) using this
new optimization scheme.
Results
Hurricane Lane synopsis. According to the National Hurricane Center (NHC) tropical cyclone
report (Beven and Wroe 2019), Lane was declared a tropical depression at 0000 UTC 15 August,
intensified into a tropical storm 12 h later, and reached hurricane status at 0000 UTC 17 August.
Rapid intensification during the next 30 h elevated the storm to category 4 strength by
0600 UTC 18 August. As Lane crossed into the central Pacific basin (nominally, west of 140°W),
it was weakened by vertical wind shear and downgraded to a category 3 storm. Soon after,
Lane reintensified back into a category 4 hurricane on 20 August, eventually reaching category
Fig. 3. Time series of fire weather variables for the time well before, during, and after Lane from 1 Jul to
15 Sep 2018 HST showing the red flag warning variables and thresholds for wildland fire danger used
by the NWS Honolulu Forecast Office (HFO). (top) Daily KBDI, as calculated by the NWS, is shown for the
Honolulu Airport. Hourly (middle) wind speed (m s–1) and (bottom) RH (%) are shown for the two NWS
stations closest to the active forest fires on Maui (Lahaina, Maui; PHJH) and Oʻahu (Kalaeloa Airport;
PHJR). Also shown are the ignition times (vertical red lines) indicating the start times of the west Maui
fires during the early morning on 24 Aug 2018 (Kauʻaula and Kāʻanapali fires) and the west Oʻahu Kahe
Point Power Plant fire at midday on 24 Aug 2018.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E960
5 intensity just after 1800 UTC 21 August (as determined by NOAA aircraft; Beven and Wroe
2019). Lane peaked with 160-mph winds and a central pressure of 926 hPa on 22 August, while
located approximately 320 miles (515 km) south-southeast of the island of Hawaiʻi. As Lane
approached the Hawaiian Islands, it began to weaken as vertical wind shear intensified once
again, and was downgraded to a tropical storm at 0600 UTC 25 August. The initial westward
track of Lane was controlled by the semipermanent high pressure system located to the
northeast of the Hawaiian Island chain. As the high pressure system weakened (on 23 August),
Lane made a near 90° turn north and in multiple forecasts from 20 to 23 August, the cone of
uncertainty allowed for landfall on Oʻahu and Maui at hurricane strength. Instead, the storm
was weakened as a result of vertical wind shear, thus allowing the lower level trade winds to
advect it westward, prompting a second 90° turn in the storm track and removing the threat
of landfall on any of the main Hawaiian Islands. Lane’s initial path, strength, and late August
timing were reminiscent of Hurricane Dot (1959). The primary differences between the two
storms being that Dot continued to move Northward while Lane was advected westward before
landfall and Lane produced significantly more rainfall than Dot for the Hawaiian Islands.
As Hurricane Lane approached the island chain, the island of Hawaiʻi was located in
the right-front quadrant of the storm, a favorable area for enhanced convective activity and
precipitation in hurricanes (Corbosiero and Molinari 2003; Lonfat et al. 2004). Although the
center of Lane did not pass closer than 140 miles (225 km) from the island of Hawaiʻi, its large
circulation and slow translation speed brought prolonged torrential rains which resulted in
flooding, mudslides, and landslides across many parts of the island of Hawaiʻi and various
other parts of the state.
Environmental evolution. Meteorological time series are shown for fire weather variables
from 1 July to 15 September 2018 at Kalaeloa Airport, Oʻahu, and Lahaina, Maui, in Fig. 3. The
closest approach of Lane (131 mi or 212 km) from Honolulu occurred at 1200 UTC (0200 HST)
25 August. The fire weather variables indicate that preexisting drought and high winds due
to Lane were key factors driving fire occurrence and spread. KBDI values crossed and re-
mained above the Red Flag threshold of 600, suggesting increased risk of fire danger from 18
to 26 August at the wildfire locales. Furthermore, the U.S. Drought Monitor for the same time
period indicated “abnormally dry” to “moderate drought” conditions at those same locations.
The most anomalous weather condition during the Lane influence period was the elevated
surface wind speeds recorded at both the Lahaina and Kalaeloa station on 24 August, coincid-
ing with the initiation of the Oʻahu and Maui fires. Winds at Lahaina clearly exceeded the red
flag threshold (8.9 m s–1 or 20 mph for >2 h), while winds at Kalaeloa, though elevated, did not
cross the Red Flag threshold. This is perhaps due to the station position south of, rather than
downwind of the Waiʻanae mountain range. Minimum RH reached near or below the Red Flag
threshold (45%) at Kalaeloa on 21 August (43%) and 22 August (46%) as Lane approached,
but was above the threshold at both stations at the time of the fires.
Shifts in atmospheric conditions were also observed throughout the atmospheric column
preceding and during the passage of Lane (Fig. 4) from vertical atmospheric profile data re-
trieved from the Hilo sounding for the period 16–31 August 2018. As Lane approached (21–22
August), temperatures were slightly elevated at all significant levels and vapor pressures were
slightly depressed. This observed warming and drying was followed by a steep rise in vapor
pressure (beginning on 22 August) especially in the midlevels, along with maxima in wind
speeds occurring throughout the vertical profile (23–24 August).
Wildfires. Beginning on 24 August, three wildfires were detected on Maui and one on Oʻahu,
all of which occurred on the drier, leeward slopes of both islands. The incidents on Maui in-
cluded (i) a 28-ha fire at Mā‘alaea ignited at 2300 HST 23 August, self-extinguished due to heavy
rainfall generated by the storm that was not included in our analysis; (ii) a 896-ha fire near
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E961
Lahaina (the “Kauaʻula Fire”)
that ignited at 0100 HST 24
August; and (iii) a 119-ha fire
at Kā‘anapali that ignited
at 0730 HST 24 August. On
Oʻahu, a 162-ha fire ignited
near the Kahe Point Power
Plant around 1100 HST 24
August. Nonnative, fire-
prone grass- and shrublands
accounted for more than 85%
of the area burned. Available
agricultural census data in-
dicates that all lands burned
were under agricultural land
use as of 1980 (sugarcane on
Maui and pasture on Oʻahu),
but abandoned by the most
recent census in 2015 (State
of Hawaiʻi Office of Planning
2019; Perroy et al. 2016).
The causes of the Maui fire ignitions remain unknown; however, the Honolulu Fire Depart-
ment attributed the Oʻahu fire to arcing from electrical lines caused by high winds generated
by Lane. Lightning was not a factor as there was little to no precipitation, and no thunder-
storms near Maui or Oʻahu at the time the fires began. The Kauaʻula and Kā‘anapali fires on
Maui required significant suppression resources including more than 70 county firefighters
aided by state airport fire crews (Wilson 2018). Both fires grew rapidly within the first 12 h
until approximately 1300 HST 25 August, after which the fires were contained and eventually
extinguished approximately 30 h from the start time of the largest fire, the Kauaʻula Fire. On
Oʻahu, 54 firefighters worked to contain the blaze with strong, downsloping winds contributing
to erratic fire behavior, grounding air support, and creating difficult conditions for suppres-
sion. According to land managers on site at the time of the fire, the downslope winds also
appeared to help contain the fire within the bowl-shaped valley and prevent fire spread farther
upslope into forested areas of the watershed (T. Anuheali‘i 2018, personal communication).
Rainfall. While wildfires coincided with Lane on Maui and Oʻahu, continuous long-duration
rainfall plagued the island of Hawaiʻi. During the closest passage of Lane (22–25 August)
the east (windward) side of the island of Hawaiʻi received nearly continuous rain. Over this
4-day period, the daily island areal means (calculated as the island means from the 250-m
gridded surface) were 93, 121, 162, and 48 mm, respectively, and the 4-day event areal mean
was 424 mm. A maximum single-day rainfall total (0000–0000 HST) of 646 mm (25 in.) was
recorded at a meteorological station on the northeast side of the island of Hawaiʻi (at Pua‘ākala)
on 22 August and a 4-day event maximum of 1,444 mm (57 in.) was recorded to the southwest
of Hilo at the Waiākea Uka station. Overall, the instrumental record (dating back to 1949) sug-
gests that Lane was the wettest hurricane ever recorded in the state of Hawaiʻi (NWS 2018),
and had the second highest storm total rainfall from a tropical cyclone in the United States,
second only to Hurricane Harvey (2017) (Beven and Wroe 2019).
The spatial distribution of the rainfall during the Lane event on the island of Hawaiʻi is
shown in Fig. 5. The highest precipitation totals were focused just to the west and southwest
of Hilo on the eastern (windward) slopes of the island. The summits of the tallest mountains
Fig. 4. Time series of (top) temperature (°C), (middle) vapor pressure (hPa),
and (bottom) wind speed (m s–1) from 16 to 31 Aug 2018 from the Hilo
radiosonde balloon sounding (PHTO). The lowest five significant levels are
included for each: 1000 (red), 925 (green), 850 (cyan), 700 (blue), and 500 hPa
(magenta). PWAT (mm; black) is also included on the middle panel. The Lane
influence period is shaded in light gray.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E962
(Mauna Kea and Mauna Loa) as well as
the western (leeward) side remained
fairly dry by comparison. Heavy rainfall
also occurred on the exposed windward
areas of Maui and Oʻahu as the storm
moved westward, however, it was not
nearly as extreme as it was on the island
of Hawaiʻi. The single station 4-day
rainfall maxima over the same period,
22–25 August, for Maui and Oʻahu, were
457 and 151 mm, respectively.
The 4-day Lane event produced more
rainfall than any other 4-day period in
the 25-year (1990–2014) gridded time
series available for the island of Hawaiʻi.
Areal mean rainfall for Lane (424 mm)
was 43.2% greater than the largest 4-day
total areal mean identified in the grid-
ded time series (17–20 November 1990;
296 mm). The single-day station high
during Lane (646 mm) was 22.3% greater
than the largest daily rainfall recorded
on the island of Hawaiʻi (528 mm) and
19.8% greater than the largest daily
rainfall anywhere in the state (539 mm)
within the 25-year daily rainfall record. The continuous and steady nature of the rainfall from
Lane on the windward side of the island of Hawaiʻi over 4 days made this event especially notable.
Impacts. The Hawaiian Islands suffered considerable damage as a result of the passage of
Lane. Multiple wildfires in west Maui destroyed 21 structures and 30 vehicles, forced the
evacuation of 100 homes, and the relocation of a hurricane shelter. Record-breaking rainfall
caused severe flooding and landslides, leading to road closures across the island of Hawaiʻi.
Road closures dramatically reduced accessibility, since impacted roads were often the only
access roads, cutting off entire sections of coastline and communities from municipal resources
and aid (see sidebar “Complications to emergency response”). For example, on 24 August,
the only road along the windward (northeast) coast of the island of Hawaiʻi (Highway 19) was
closed due to 14 landslides within a 25-mile stretch. Torrential rains also forced more than
100 people to evacuate from their homes on the island of Hawaiʻi, primarily in the area near
Hilo. Poststorm assessments found 30 businesses and 152 homes damaged, 29 of the homes
with major damage from flooding (Burnett 2018). On Maui, rainfall from Lane was blamed
for one death, landslides there also blocked roadways, and one roadway collapsed due to a
sinkhole (Peterkin 2018). The total estimate of damage costs for the state of Hawaiʻi (including
damage from flood and fires) was US$250 million (Aon 2019).
Discussion
The simultaneous occurrence of extreme precipitation and wildres during the passage of
Lane provides a new perspective on the range of hazards associated with a hurricane event.
Here, interactions between the atmospheric and biophysical conditions are discussed with
respect to the hurricane environment to show how they exacerbated hazards and created
favorable conditions for wildres.
Fig. 5. Total accumulated rainfall (mm) during Hurricane Lane,
from 22 to 25 Aug 2018 on the island of Hawaiʻi. Hillshade is
included along with white dashed contours indicating terrain
height every 500 m.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E963
Fires on both Maui and Oʻahu
ignited in areas dominated by
nonnative grasses, known to
respond quickly to changes in
precipitation and contribute to fire
risk both by accumulating biomass
during wet periods and rapidly
drying out during dry periods
(Trauernicht 2019). The 2017/18 wet
season (November–April) was rela-
tively wet compared to historical
means at most stations across the
state (NWS/HFO 2018b) resulting
in grass accumulation (Trauernicht
2019). During the 3 months leading
up to Lane (May–July), a drying
pattern was observed in leeward
areas across the state with many
leeward stations receiving <50%
of their long-term average rainfall
(NWS/HFO 2018b). In west Maui,
the NOAA/NWS station located
140 m from the Lahaina fire re-
ported rainfall 3% and 8% of the
long-term average for the months
of June and July, respectively, and
over the 3 weeks leading up to the
Lane event, only 5 mm of accumu-
lated rainfall was observed at this
location (NWS/HADS 2018). Dry conditions were also observed at a climate station ~4 km
upslope of the Oʻahu fire. This pattern of wet months followed by dry months led to a surplus
of dead, dry grass (i.e., fuel) on the ground, increasing the risk of fire.
Over the days of Lane’s approach and preceding wildfire ignitions, drought conditions
steadily worsened as indicated by the KBDI. Under well-developed drought, the condition of
the vegetation (e.g., plant moisture content and the proportion of dead to live vegetation) was
well suited to support combustion. Compounding these drought conditions on the ground,
the atmospheric conditions as Lane approached exacerbated the risk of fire. Wind is the pri-
mary driver of fire spread, which can develop especially rapidly in the fine, grassy fuels that
dominated the burn areas (Cheney and Sullivan 2008). It can also contribute to ignitions by
knocking down power lines, as observed with the Oʻahu fire. The recorded strong, erratic
winds at both locations grounded helicopters, which are a critical resource for fire suppres-
sion in Hawaiʻi’s steep terrain.
The geographical location of the fires on exposed leeward slopes, the reports from local fire
officials, and the observed strong winds on both Maui and Oʻahu suggest that dynamically
driven downslope winds (Elvidge and Renfrew 2016) contributed to the occurrence and spread
of fire during Lane. Downslope winds on the lee sides of the Hawaiian Islands are common,
and enhanced wind speeds from the hurricane environment at the 850- and 700-hPa levels
(Fig. 4) likely amplified these winds further. Downslope winds occur once orographically
lifted air transits the peak of a mountain and begins to descend on the lee side, resulting in
an increase in speed, and often both warming and drying of the air due to its descent, and
Complications to Emergency Response
An additional hazard brought on by Lane arose from the limitations
imposed on emergency managers. The simultaneous occurrences of
high winds, res, ooding, and landslides across the islands strained the
capacity of emergency responders, limiting their ability to assist in other
hurricane-related incidents, such as evacuations, medical emergencies,
and road clearing. In some areas on the island of Hawaiʻi, ooding and
landslides led to road closures that essentially cut off entire sections of
coastline and communities from municipal resources and aid.
The majority of the state’s 1.43 million people and associated infra-
structure are located in coastal zones and thus highly vulnerable to the
many hazards associated with the passage of a hurricane. Current storm
emergency response plans involve sheltering in place or moving inland
to areas of higher elevation (Wolshon et al. 2005). Furthermore, the
state is more than 3,900 km from the continental United States, compli-
cating and delaying the arrival of outside emergency assistance in the
wake of a natural disaster. A recent analysis by the Hawaiʻi Emergency
Management Agency highlighted the vulnerability associated with having
only one harbor capable of accommodating high-volume container ships
and only a 5–7-day supply of food available in the islands at any given
time (Hara 2018). The population of the state is expected to reach 1.65
million by 2045 (Kim et al. 2018), which will put additional strains on
food supplies, land resources, and emergency response.
To fully understand the vulnerability of populations to extreme
weather events such as Lane, the full spectrum of risk associated with
the natural hazards produced by an event and the social responses to
these hazards must be considered. For Hawaiʻi, this is especially impor-
tant considering access to emergency services from the U.S. mainland
is limited and, in the event that damage occurs to the shipping ports or
airports, access to the islands and the distribution of emergency supplies
could be compromised.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E964
due to mixing of upper-level dry air downward. This typical signature of warm, dry air in the
downslope wind is not visible during Lane from the surface stations, but relatively dry air
was present in the midlevels (Fig. 4).
A distinct drying signal was seen as Lane approached the state. Weak broadscale subsid-
ence is often found just outside the periphery of a hurricane, characterized by slowly sinking
air that is warm and dry, as a result of compression upon descent. Prior work showed this
subsidence region surrounding a storm visible from satellite images as a cloud-free ring (Fett
1964). Water vapor channel satellite images (not shown) of Lane as it approached the state
(19–21 August) clearly showed a similar dry, cloud-free ring or “hurricane lei” (a term coined
here) surrounding Lane, which is a result of either subsidence or advection of dry air around
the storm periphery. The hurricane lei effect can be seen in the surface stations as a drop in
the minimum RH, precipitable water (PWAT), and vapor pressure prior to Lane’s arrival on
21–22 August (Figs. 3 and 4). Although lower RH increases fire intensity and rate of spread,
the observed atmospheric drying in the hurricane lei occurred prior to the fire ignitions and
therefore did not directly contribute to fire danger in this case. Instead, longer term drought
conditions strongly contributed to fire potential due to its effect on fuel curing, and the
elevated wind speeds in the storm environment were the largest direct factor influencing fire
development. Low humidity in the atmosphere increases fire risk over short-term (hourly) time
scales by decreasing fuel moisture in standing vegetation, thereby increasing the likelihood
of combustion and the energy released by the fire (i.e., fire intensity, Viney 1991; Beverly and
Wotton 2007). While low humidity was not a factor during the Lane event, the potential for
the hurricane lei drying effect to enhance fire risk should not be overlooked. Three weeks
prior to Lane, the approach of Hurricane Hector was also associated with low humidity,
and large fires on Oʻahu and the island of Hawaiʻi raised concerns among NWS forecasters
over increased fire intensity due to the abnormally dry conditions (D. Wroe 2018, personal
communication). Moreover, Hawaiʻi has some of the highest recorded densities of wildfire
ignitions (e.g., number of fires per square kilometer per year), caused primarily by human
activity (Trauernicht and Lucas 2016) and, thus, has near-constant risk of wildfire initiation.
Extreme rainfall due to the interaction of tropical cyclones with mountains is common
(DeHart and Houze 2017; Smith et al. 2009; Li et al. 2007; Wu et al. 2002). Many important
criteria for heavy orographic precipitation were present during Lane including a moisture rich
environment, steady upslope winds, and the presence of a large, preexisting, slow-moving,
convective system (Lin et al. 2001). The moisture rich environment is visible as an increase in
PWAT (22 August) that coincides with an increase in the 700-hPa vapor pressure, suggesting
a deepening of the marine boundary layer (Fig. 4). The deepening is accompanied by a slight
simultaneous downward shift in the 700-hPa temperature consistent with the disappearance
of the trade wind inversion. Without this low-level temperature inversion, deep convection
can more easily develop in the environment. Finally, enhanced winds at mid- and upper levels
concurrent with these moist unstable conditions led to strong wind shear between 850 and
500 hPa, which intensified convection and helped to bring extreme rainfall to the island of
Hawaiʻi (Callaghan 2019).
The presence of these important ingredients for extreme rainfall makes it no surprise that
Lane produced a record-breaking rainfall event. The simultaneous occurrence of extreme pre-
cipitation and wildfires, however, is uncommon and provides a new perspective on the range
of hazards associated with a hurricane event under certain biophysical and atmospheric condi-
tions. The fires on Maui and Oʻahu are explained by a number of these interacting conditions.
First, all of the fires occurred in areas dominated by nonnative grasses. Second, the wet and
then dry rainfall pattern preceding the event created an abundance of fuel. Finally, windy
conditions were driven by the storm environment and topography. Consequently, the fires
spread rapidly across the landscape due to the abundance of fine, grassy fuels and strong
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E965
winds creating firefighting conditions the deputy fire chief described as “some of the most
adverse the Maui Fire Department has faced in recent history” (Osher 2018).
While the Lane example is only one case study connecting a hurricane to fires, future
changes are expected to increase the risk of both in Hawaiʻi. Over the last 60 years, Hawaiʻi
has seen >60% decline statewide in the land areas under agricultural production, including
cultivated crops and ranching (Trauernicht et al. 2015; Perroy et al. 2016). These abandoned
agricultural lands are now covered with the same nonnative fire-prone grasses and shrubs
that burned during Lane, which currently comprise nearly 25% of state land. With rising
costs of labor and the increasing value of real estate in Hawaiʻi, continued declines in agricul-
tural production are replaced by increased residential development (Suryanata 2002). These
land-use changes are compounded by an observed trend of drying in the area (Frazier and
Giambelluca 2017), both of which are expected to further increase the risk of fire in Hawaiʻi
in the future (Trauernicht 2019). As for the connection of fire and hurricanes, we note that
hurricane season in the central Pacific (1 June–30 November) coincides with the dry season
(May–October) and the climatological peak in KBDI, illustrating an ongoing connection
between hurricanes and fire risk in Hawaiʻi that requires further investigation.
Hurricane risk in Hawaiʻi and the Pacific region in general is also expected to increase. A
warming climate increases the amount of energy available to fuel storms, thus supporting
the formation of stronger storms (Knutson et al. 2010; Bengtsson et al. 2007; Bender et al.
2010) and an increase in storm driven precipitation (e.g., Knutson et al. 2010; O’Gorman and
Schneider 2009). Another influence on precipitation comes from a projected global slow-down
of storm translation speed (Kossin 2018) allowing local precipitation totals to increase when a
storm spends more time over a given location. Finally, studies suggest a poleward shift of the
location of storm maximum intensity (Kossin et al. 2014). For Hawaiʻi specifically, changes in
the North Pacific semipermanent high pressure ridge and changes in the strength of vertical
wind shear in a changing climate are important. Projections by Murakami et al. (2012) showed
an increase in tropical cyclones in the central Pacific near Hawaiʻi by late century.
Concluding remarks
Lane brought to light the risk of compounding hazards associated with the passage of a hur-
ricane in the Hawaiian region. From this study we document what we believe to be the rst
instance of a hurricane causing both heavy rainfall and contributing to multiple instances
of re simultaneously. Future research eorts are needed to examine whether this is an iso-
lated instance, or whether these types of compounding hazards have occurred elsewhere
or previously. Additional research will help to determine if this particular instance of hur-
ricane–re connection is an artifact of global changes to the global climate system that may
become more common in the future. A complete understating of these factors is critical to
understanding the vulnerability of people and resources exposed during a severe weather
event. This is especially of interest in the context of a changing climate where intensity and
frequency of compounding extreme events is likely to increase (e.g., Mora et al. 2018).
Acknowledgments. We appreciate constructive criticism from three reviewers, and discussions with
the National Weather Service (NWS) Honolulu Forecast Office (HFO), especially Kevin Kodama, who
provided additional rainfall datasets and knowledge of the storm precipitation and hydrology. GOES
images were provided by Randall Alliss (Northrop Grumman Corporation), and support for the Hawaiʻi
EPSCoR Program is provided by the National Science Foundation’s Research Infrastructure Improve-
ment (RII) Track-1: ‘Ike Wai: Securing Hawaiʻi’s Water Future’ Award OIA-1557349.
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AMERICAN METEOROLOGICAL SOCIETY JUNE 2020 E966
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