Tuesday, 8 January 2019: 1:30 PM
North Ballroom 120CD (Phoenix Convention Center - West and North Buildings)
On the 14th of April, 2018 the 24-hour U.S. rainfall record was broken. It occurred
as part of an extreme, multi-day, rainfall event that impacted the island of Kauai, Hawaii.
An extremely moist unstable flow impinged on the slopes of Mt. Wai'ale'ale, inundating the
island with up to ~50 inches of rainfall in a 24-hour time period, decimating the old record
of 43 inches set in Alvin, Texas in 1979. Several factors conspired to break the U.S. rainfall
record, including i) a slowly propagating upper-level trough, ii) a deep layer of moist low-
level easterly flow, iii) pronounced orographic forcing and anchoring of thunderstorms
along the north-eastern slopes of Mt. Wai'ale'ale, and iv) a strong southwesterly flow aloft
providing ample wind shear and exhaust. The combination of these conditions resulted in
sustained deep convection, heavy rainfall, and frequent lightning. Mesoscale analyses
benefit from sub-hourly rain-gauge data and GLD360 lightning strike densities. Additionally,
high resolution numerical simulations employing the Weather Research and Forecast(WRF)
model with data assimilation were used to further analyze this extraordinary event. The
island terrain in the WRF model was modified to improve terrain resolution to more
accurately account for the steep slopes and cirques of Mt. Wai'ale'ale, thus allowing the
contribution of orographic vertical motion to the record rainfall distribution to be
investigated.
as part of an extreme, multi-day, rainfall event that impacted the island of Kauai, Hawaii.
An extremely moist unstable flow impinged on the slopes of Mt. Wai'ale'ale, inundating the
island with up to ~50 inches of rainfall in a 24-hour time period, decimating the old record
of 43 inches set in Alvin, Texas in 1979. Several factors conspired to break the U.S. rainfall
record, including i) a slowly propagating upper-level trough, ii) a deep layer of moist low-
level easterly flow, iii) pronounced orographic forcing and anchoring of thunderstorms
along the north-eastern slopes of Mt. Wai'ale'ale, and iv) a strong southwesterly flow aloft
providing ample wind shear and exhaust. The combination of these conditions resulted in
sustained deep convection, heavy rainfall, and frequent lightning. Mesoscale analyses
benefit from sub-hourly rain-gauge data and GLD360 lightning strike densities. Additionally,
high resolution numerical simulations employing the Weather Research and Forecast(WRF)
model with data assimilation were used to further analyze this extraordinary event. The
island terrain in the WRF model was modified to improve terrain resolution to more
accurately account for the steep slopes and cirques of Mt. Wai'ale'ale, thus allowing the
contribution of orographic vertical motion to the record rainfall distribution to be
investigated.
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