HomeMy WebLinkAboutCommunication No. 2026-12 Kau Flooding Events and Drivers Civil Defense ReportSelected Impactful Rain Events - Kaʻū District
National Weather Service
Communication No. 2026-12
RECENT IMPACTFUL RAIN EVENTS
The March 2026 Kona Lows
Back-to-back storm systems brought prolonged heavy rainfall to Hawaiʻi Island. The first system produced 15
to 25 inches of rain across the Kaʻū District, with localized areas receiving over 30 inches. The rainfall led to
overflowing streams, landslides, and roadway closures. A second system moved over the saturated ground
on March 23, producing thunderstorms with rainfall rates of over 4 inches per hour from Pāhala through Hilo,
which resulted in additional road closures.
The February 2023 Kona Lows
Two Kona lows affected the state, resulting in notable flooding across the Kaʻū District. The first storm
produced 15 to 25 inches of rain across southeastern Hawaiʻi Island, with rainfall rates exceeding 3 inches per
hour at Kapapala Ranch. The resulting runoff led to several road closures, including Wood Valley Road,
Kaalaiki Road, and Highway 11 at Kawa Flats. Due to the high soil moisture from this initial system, a second
storm on February 20 and 21 caused additional runoff that closed Highway 11 at Kawa Flats again.
The November 2000 Event
In early November 2000, the remnants of a tropical storm brought catastrophic flooding to parts of Hawaiʻi
Island, including the Kaʻū District. The highest precipitation occurred between November 1 and November 2,
when a gauge at Kapapala Ranch near Pāhala recorded 38.97 inches of rain. The flooding damaged or
destroyed four bridges along the Mamalahoa Highway, temporarily closing the primary route between
Pāhala and Hilo and leading to a federal disaster declaration.
METEOROLOGICAL DRIVERS OF FLOODING
Meteorological Similarities
The March 2026, February 2023, and November 2000 events share a fundamental meteorological pattern:
they were all driven by large-scale, slow-moving low-pressure systems. These systems disrupted the typical
northeasterly trade winds and drew deep plumes of warm, equatorial moisture northward over the state.
Wind Direction and Orographic Lift
During all three events, the counter-clockwise circulation of the low-pressure systems generated southerly
winds. This shift in wind direction is a contributing factor for extreme rainfall. When these moisture-laden
winds encounter the island's topography, the air is mechanically forced to rise. As the air ascends, it expands,
cools, and condenses its water vapor into rain—a process known as orographic lift.
Why the Kaʻū District Was Highly Impacted
The pronounced impacts in the Kaʻū District are a direct result of its geography. The district is located on the
expansive southern and southeastern slopes of Mauna Loa. While it is somewhat sheltered during normal
trade-wind patterns, it is fully exposed to southerly and southeasterly wind flows.
When anomalous low-pressure systems drive deep tropical moisture directly into the broad, high-elevation
slopes of Mauna Loa, the resulting orographic lift is highly efficient. The mountain acts as an orographic
barrier, anchoring rain bands in place and continuously wringing out moisture as long as the southerly winds
persist. This localized, sustained rainfall rapidly exceeds the soil's infiltration capacity, leading to rapid runoff
and significant flash flooding in the drainages and communities below.
KONA LOWS OF MARCH 10-24, 2026
Event Summary
Between March 10 and March 24, 2026, the Hawaiian Islands experienced a historic weather disaster driven
by back-to-back storm systems. The first major storm delivered its heaviest rainfall from Tuesday, March 10,
through Monday, March 16. This phase dropped 15 to 25 inches of rain across portions of Hawaiʻi
Island—including the Kaʻū District—with localized areas seeing over 30 inches. Most of this rain fell during
a single 24 hour period on March 14. As one of the hardest-hit areas in the state, the southern half of the
Hawaiʻi County suffered from overflowing streams, landslides, road closures, and significant flooding of
homes and businesses, while severe winds downed trees and caused widespread power outages.
Because the ground was already entirely saturated, a second storm system easily triggered additional
flooding the following week. The heaviest rain for the Big Island during this second wave arrived on March
23, bringing intense thunderstorms with rainfall rates of over 4 inches per hour stretching from Pāhala (in
the Kaʻū District) through Hilo. Fortunately, the impacts on the Big Island during this final round were
primarily limited to road closures from heavy ponding before the skies finally cleared on March 24.
KONA LOWS OF MARCH 10-24, 2026
PRECIPITATION ANALYSIS
During the Kona Lows of March 2026
the nearest weather stations to
Waiʻōhinu received around 30” of
rainfall.
The majority of this rain fell on 3/14.
An additional heavy rain event
impacted the Pāhala area on 3/23.
Location Total
Pahala (15004)32.14
Kaiholena (UHM)29.32
Kapapala Ranch (15003)30.22
KONA LOWS OF MARCH 10-24, 2026
DAILY PRECIPITATION
Of the ~30” that fall during both
Kona Storms the majority of the rain
occurred on one day (3/14). Each of
the three closest weather stations
recorded over 15” during this
particular 24 hour period.
There was an additional heavy rain
day on 3/23, which primarily
impacted areas from Pāhala into the
lower Puna District.
Location 3/10/2026 3/11/2026 3/12/2026 3/13/2026 3/14/2026 3/15/2026 3/16/2026 3/17/2026 3/18/2026 3/19/2026 3/20/2026 3/21/2026 3/22/2026 3/23/2026 3/24/2026
Pahala (15004)0.01 0.96 0.36 1.78 17.66 0.37 1.88 0.55 0.46 0.09 0.02 0.04 0.38 7.12 0.46
Kaiholena (UHM)0.07 0.55 0.49 3.86 20.80 0.37 0.19 0.27 0.94 0.13 0.07 0.02 0.35 0.78 0.43
Kapapala Ranch (15003)0.00 0.39 0.41 2.60 18.99 0.46 0.58 0.95 0.78 0.13 0.01 0.88 0.46 3.88 0.20
RADAR ESTIMATES
Radar estimates suggest
upwards of 20” of rain fell
in the higher terrain above.
The lower values values
near Nāʻālehu are an
artifact due to the local
terrain blocking the radar
beam.
KONA LOWS OF MARCH 10-24, 2026
MARCH
10
Little to no rain
MARCH
11
Light Amounts
MARCH
12
Light Amounts
MARCH
13
Rain Amounts Increase
MARCH
14
Peak Rainfall Day
KONA LOWS OF MARCH 10-24, 2026
MARCH
15
Light Amounts
MARCH
16
Light Amounts
MARCH
17
Light Amounts
MARCH
18
Light Amounts
MARCH
19
Light Amounts
KONA LOWS OF MARCH 10-24, 2026
MARCH
20
Light Amounts
MARCH
21
Light Amounts
MARCH
22
Light Amounts
MARCH
23
Second Peak Rain Day
Pāhala area
MARCH
24
Light Amounts
KONA LOWS OF FEB 16-21, 2023
Summary
In mid-February 2023, a pair of Kona low storm systems brought severe flash flooding to the state. The first
storm began impacting the Big Island late on Thursday, February 16, and intensified on the morning of Friday,
February 17. The Kaʻū District was hit heavily during this initial wave, with flooding forcing the closure of
Highway 11 at Kawa Flats, Wood Valley Road, and Kaalaiki Road. The heavy rain intensified further early
Saturday morning, with automated gauges (including at Kapapala Ranch) recording extreme rainfall
rates of more than 3 inches per hour. This kept several roads impassable across the Kaʻū and Puna districts
until the storm finally diminished on Saturday night.
After a brief break on Sunday, February 19, the second storm system arrived. While its heaviest rainfall
focused primarily on Kauaʻi and Oʻahu, it still dropped rain over the slopes of the Kaʻū District on Monday,
February 20. Even though the rainfall totals on the Big Island were relatively low during this second wave,
the ground was already saturated from previous system. This caused immediate runoff and another
episode of flooding that once again shut down Highway 11 at Kawa Flats.
KONA LOWS OF FEBRUARY 16-21, 2023
DAILY PRECIPITATION - FEB 17, 2023
RADAR ESTIMATES
Radar estimates suggest the heaviest rain fell from February 16-18, 2023. Additional lighter rain amounts
occurred through February 21st.
DAILY PRECIPITATION - FEB 18, 2023
FLOODING OF NOV 1-3, 2000
Summary
In early November 2000, the remnants of Tropical Storm Paul interacted with an upper-level trough resulting
in thunderstorms and historic flooding for Hawaiʻi County. The heaviest rain fell between November 1 and
November 2, severely impacting the Kaʻū District. A rain gauge at Kapapala Ranch near Pāhala recorded
an astonishing 38.97 inches of rain, with 37.02 inches falling in just a 24-hour period. This overwhelmed
streams, carved out new flood channels, and triggered numerous landslides.
Significant to catastrophic flooding impacts occurred across the Kaʻū, Puna, and Hilo districts. Flooding
damaged or destroyed four bridges along the Mamalahoa Highway (Highway 11), and damaged or
destroyed nearly 300 homes.
FLOODING OF NOV 1-3, 2000
STORM TOTAL PRECIPITATION - FEB 17, 2023
TOTAL RAINFALL
Rain totals exceeding 30 inches we reported in portions of the
Kaʻū District during this event.
SELECT RAIN TOTALS