49 Inches Of Rain Recently Fell In One Day Over Hawaii - Is That A Record?

49 Inches Of Rain Recently Fell In One Day Over Hawaii - Is That A Record?

Marshall Shepherd , Contributor Opinions expressed by Forbes Contributors are their own.

I am a scientist that has spent much of my career studying precipitating systems. I was also the Deputy Project Scientist for NASA's Global Precipitation Measurement (GPM) Mission for many years. Big rainfall events get my attention. From the period April 14th to 19th, extremely heavy rainfall disrupted the Hawaiian Islands. In fact, a Flash Flood Watch was in effect for the entire state of Hawaii on April 19th. Preliminary reports suggest that in one case, nearly 50 inches of rainfall fell in Kauai within one day. If this is verified, it would be a new United States record for a 24-hour period. I want to also emphasize that this is another weather-related human tragedy unfolding for people affected by the flooding, loss of supplies, and so forth.

NASA/JAXA and Hal Pierce

Rainfall as measured by Global Precipitation Measurement (GPM) Mission IMERG rainfall product. NASA's IMERG, a satellite based produced, reveals the pattern of rainfall accumulation from April 10 to 16, 2018.

My colleague Professor Tom Gill of University of Texas-El Paso made me aware of this statement by the National Weather Service-Honolulu on April 25th,

Preliminary data downloaded from a remote rain gage in North Kauai indicate that rainfall during the flash flood event on April 14-15, 2018 broke the U.S. 24-hour rainfall record. The rain gauge, located in Waipa about one mile west of Hanalei, recorded 49.69 inches of rainfall during the 24-hour period ending at 12:45 pm HST April 15. This total, if certified, will break the current U.S. 24-hour record of 43 inches at Alvin, TX on July 25-26, 1979, and the state of Hawaii record of 38 inches at Kilauea (Kauai) on January 24-25, 1956

The statement goes on to note that the National Climatic Extremes Committee will convene to review the case and start the certification process.
This particular region is no stranger to wet conditions. Mount Waialeale, the second highest peak on the island of Kauai (5,148 feet above sea level) is considered by some sources as the wettest place on Earth. However, many sources place the wettest location on the planet in India at either Cherrapunji or Mawsynram. According to a Weather.com article, there is "467.35 inches per year for Mawsynram vs. 463.66 inches for Cherrapunji." The same article also notes,

Though it's no longer the world's rainiest place — despite local tourism officials' boasts — not far behind Cherrapunji is Hawaii's Mount Waialeale, which sees an average of more than 450 inches of rainfall every year. In 1982, a record 683 inches of rain fell here, which works out to nearly 57 feet.

Even it is not the "wettest" place it is certainly one of them one of them. In some of our scholarly research, we published  a new extreme rainfall metric called a Wet Millimeter Day in Geophysical Research Letters about a decade ago. Our metric was intended to provide a way to quickly quantify extreme rainfall in the spirit of how Heating or Cooling Degree Day is used by energy companies. Mt. Waialeale's average daily rainfall total was used in the initial version as the reference value for our metric though it has recently been updated in a study published in Urban Climate by me and two colleagues at the Southeast Regional Climate Center at the University of North Carolina. By the way, Jurassic Park was filmed in the lush vegetation and mountainous surroundings of Mt. Waialeale. Other very wet places on Earth include:

• Tutendo, Colombia, South America
• Big Bog, Maui, Hawaii
• Debundscha, Cameroon, Africa
• San Antonio de Ureca, Bioko Island, Equatorial Guinea
• Cropp River, New Zealand.

So what caused this particular flooding event? According to NASA, it appears that a trough (an elongated area of low pressure) disrupted typical northeast trade winds flow producing heavy rainfall as the trough strengthened and slowly drifted over Kauai.

NASA/JAXA and Hal Pierce

Intense showers detected by the GPM satellite radar on he GPM core observatory satellite flew over Kauai on April 14, 2018 at 10:01 a.m. HST (4:01 p.m. EDT/2001 UTC)

To give this 49 inch rainfall total some perspective, the highest total amount from the devastating rains associated with Hurricane and Tropical Storm Harvey (2017). According to NOAA's Climate.gov website,

The highest rainfall amount totaled 48.20 inches at a rain gauge on Clear Creek and I-45 near Houston Texas. It was the highest rainfall amount in a single storm for any place in the continental United States. At Houston’s Hobby airport, the three-day rainfall from August 26-28 was larger than the previous record for wettest 65-day period......As the storm slowly moved east, it brought its record-setting rains with it. Beaumont, TX, broke its record for wettest day on record on August 29 when over 26 inches of rain fell—more than double the previous record. August rains reached a total of 54.73 inches, more than three times the previous wettest August and almost 32 inches more than the previous all-time wettest month (November 1902).