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Hawaii State Capital Breaks Through December Rainfall Record
December 25, 2021 at 05:34 PM EST
By WeatherBug Sr. Meteorologist, Chad Merrill
While much of the Lower 48 has been hoping for rainfall in the final month of 2021, the Aloha State is begging for the clouds to part following a rough start to December.
Often times during winter, low pressure often develops on the side of the Hawaiian Island chain that normally is sheltered from prevailing winds. Since trade winds usually come from the east or northeast, that leaves the western part of the Hawaii Islands in a rain shadow with far less moisture available to squeeze out showers.
A special type of moisture-rich system, called a “kona low” adjusts the prevailing wind to the south or southwest direction. This changes the entire ball game; instead of heavy rain falling on the eastern side of the islands, the kona low pressure triggers very heavy rain on the islands’ western flank.
The moisture hose coming from the south or southwest direction is forced up Mauna Kea, the tallest mountain on Earth at 32,696 feet and Mauna Loa (elevation of 11,000 feet above sea level) where temperatures are far below freezing. The moisture condenses in the subfreezing temperatures to unleash blizzard conditions.
Meteorologists began monitoring development of a kona low pressure on Saturday, December 4, 2021 when heavy rain began to fall in Hawaii. The storm system moved over the islands on Monday, December 6 when the governor issued a state of emergency.
Two-day rainfall amounts were staggering across the Hawaii islands. Between December 5 and 6, Nene Cabin, on Hawaii’s Big Island, was drenched with 14.26 inches of rain. On Maui, the highest rain total was in Kula where 12.86 inches of rain collected in the gauge. Nuuanu Upper on Oahu was soaked with 11.68 inches of rain while the highest total on Kauai was the Lihue Airport with 3.28 inches.
The rain was heavy enough to bust through the record books in Hawaii’s state capital on December 6, 2021. Honolulu set its daily and single-day rainfall record for December while also capturing its second highest all-time single day rainfall title with 7.92 inches.
Honolulu would have needed to double this amount to tie the all-time single day rainfall record of 15.32 inches set on March 5, 1958.
Damage from the rain and wind was unsurmountable. Homes and businesses were damaged, and power was cut to downtown residents. Highway 11 through the Kawa Flats and Highway 1 through Honolulu were closed for several hours while two planes at the Honolulu Airport were damaged when an empty storage contained blew into them. The strongest wind gust measured during the Kona low event was 105 mph on Mauna Kea Summit.
The recent rainfall records set in Honolulu and the still standing all-time single day rainfall record in March of 1958 both occurred in the historically favored wettest months of the year. Honolulu averages 2.36 inches of rain in March and 2.18 inches of rain in December. November is typically the second wettest month of the year in Honolulu with 2.25 inches of rain.
Stay up-to-date with the latest severe weather alerts 24/7 by downloading the WeatherBug phone App or Desktop Application.
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Story Image: A plume of moisture-rich air is seen in this Total Precipitable Water screen capture during the Kona Low event on December 2, 2021. (Courtesy of National Environmental Satellite Data and Information Service)
Often times during winter, low pressure often develops on the side of the Hawaiian Island chain that normally is sheltered from prevailing winds. Since trade winds usually come from the east or northeast, that leaves the western part of the Hawaii Islands in a rain shadow with far less moisture available to squeeze out showers.
A special type of moisture-rich system, called a “kona low” adjusts the prevailing wind to the south or southwest direction. This changes the entire ball game; instead of heavy rain falling on the eastern side of the islands, the kona low pressure triggers very heavy rain on the islands’ western flank.
The moisture hose coming from the south or southwest direction is forced up Mauna Kea, the tallest mountain on Earth at 32,696 feet and Mauna Loa (elevation of 11,000 feet above sea level) where temperatures are far below freezing. The moisture condenses in the subfreezing temperatures to unleash blizzard conditions.
Meteorologists began monitoring development of a kona low pressure on Saturday, December 4, 2021 when heavy rain began to fall in Hawaii. The storm system moved over the islands on Monday, December 6 when the governor issued a state of emergency.
Two-day rainfall amounts were staggering across the Hawaii islands. Between December 5 and 6, Nene Cabin, on Hawaii’s Big Island, was drenched with 14.26 inches of rain. On Maui, the highest rain total was in Kula where 12.86 inches of rain collected in the gauge. Nuuanu Upper on Oahu was soaked with 11.68 inches of rain while the highest total on Kauai was the Lihue Airport with 3.28 inches.
The rain was heavy enough to bust through the record books in Hawaii’s state capital on December 6, 2021. Honolulu set its daily and single-day rainfall record for December while also capturing its second highest all-time single day rainfall title with 7.92 inches.
Honolulu would have needed to double this amount to tie the all-time single day rainfall record of 15.32 inches set on March 5, 1958.
Damage from the rain and wind was unsurmountable. Homes and businesses were damaged, and power was cut to downtown residents. Highway 11 through the Kawa Flats and Highway 1 through Honolulu were closed for several hours while two planes at the Honolulu Airport were damaged when an empty storage contained blew into them. The strongest wind gust measured during the Kona low event was 105 mph on Mauna Kea Summit.
The recent rainfall records set in Honolulu and the still standing all-time single day rainfall record in March of 1958 both occurred in the historically favored wettest months of the year. Honolulu averages 2.36 inches of rain in March and 2.18 inches of rain in December. November is typically the second wettest month of the year in Honolulu with 2.25 inches of rain.
Stay up-to-date with the latest severe weather alerts 24/7 by downloading the WeatherBug phone App or Desktop Application.
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Story Image: A plume of moisture-rich air is seen in this Total Precipitable Water screen capture during the Kona Low event on December 2, 2021. (Courtesy of National Environmental Satellite Data and Information Service)