Although much media attention weather-wise (at least recently) for Hawaii has been about tropical storms (Kilo’s possible impact on the Hawaiian Isles and some more in the pipeline) an even more interesting story has been the exceptional rainfall that has drenched the islands in recent days and the on-going record hot summer. Despite a record warm July, accumulating snow managed to dust the summit of Mauna Kea on the Big Island. Here are some details about the above events.
August Rainfall Records
A deep plume of moisture associated with the passage of Tropical Storm/Depression Kilo overran much of the Hawaiian Island chain on September 23-24. Honolulu received its greatest August rainfall for both a calendar day (3.59” on August 24th) and for a 24-hour period (4.42” August 23-24). The previous calendar day August record was 2.92” on August 4, 2009. In addition, Honolulu now has also surpassed its August monthly rainfall record with a 5.64” total (as of August 25th) surpassing the previous record for such of 4.47” set in August 1888. The precipitation POR for Honolulu dates back to 1877. What is also remarkable is that until this month, Honolulu had seen a TOTAL of only 3.59” of precipitation since the beginning of the year (January through July).
Kahului on Maui Island, also broke its August calendar day rainfall record with 1.46” on August 24th (previous record 1.13” on August 1, 1982) and its monthly August record as well: 2.12” as of August 25th, previous record 1.54” in August 1982.
Lihue on Kauai came very close to breaking its August calendar day rainfall with 5.28” on August 24th, just shy of the record 5.31” measured on August 6, 1959. So far this month (as of August 25th) 7.39” has accumulated, closing in on the August monthly record of 8.19” set in 1959.
Hilo on the Big Island has picked up 16.88” so far this month, some 8.77” above average to date (August 25th) but a long way from the August record of 26.92” seen in 1991.
Anomalously high sea surface temperatures this summer have, no doubt, played a role in the record warmth and tropical storm formation associated with the recent rainfall events.
Temperatures: Many Records Established
More impressive than the recent rainfall have been the extraordinary warm temperatures experienced across the island chain this summer.
July was the warmest month on record (any month) for Hilo with a 79.4° average temperature, surpassing by a large margin (for a tropical location) the previous such of 78.5° set in August 1994. Furthermore, 12 of the 31 days of July set or tied a daily record high. So far this August, nine out of the past 25 days have also achieved record daily high status. On August 22nd, the daily low temperature of 77° was the warmest minimum ever observed at the site (76° was the previous record set on three former occasions and once again on August 23rd this month). With just six days left to the climatological summer, the average temperature since June 1st has been 78.6°, so it is very likely this will be the warmest summer on record for Hilo, besting the previous such observed in 1986 when the summer average was 77.6°. The temperature POR for Hilo begins in 1949 according to NOW data.
Daily record highs for Hilo, Hawaii. So far this climatological summer (as of August 25th) there have been 23 daily record highs: 2 in June, 12 in July, and 9 so far this August.
Honolulu experienced six record daily highs in July and two so far this August including a 93° reading on August 12th which ties their all-time August monthly record (set on 14 other occasions however!). Honolulu’s all-time record high is 95° registered on September 19, 1994. On August 22nd the minimum temperature of 81° set a new all-time (any month) record high-low. The previous record of 80° has occurred before on six different days, the most recent being August 1, 2004. July was the warmest such on record with a 83.3° average (previous July monthly record being 83.2° in 1995). Despite, all the warmth there is little chance that either an all-time new monthly or summer record will be broken: monthly record being 84.3° in August 1994 and the warmest summer being that of 2005 with an 83.1° average. Temperature POR for Honolulu begins in 1890.
Lihue also had its warmest July on record with a 80.7° average (tied with 1982). So far this August the average temperature has been 81.5° which, if it holds, will make this the hottest month (any month) on record, beating out the 81.2° set in August 1980. The summer so far has averaged 80.2°, just shy of the record of 80.3° observed during the summer of 1996. The 90° observation August 23rd ties the August monthly heat record (on five other occasions) and is 1° short of their all-time heat record of 91° set on seven different days in the past. POR for temperatures since 1905 according to NOW data.
Kahului observed its warmest month (any month) on record this past July with a 81.7° average (previous record 81.5° in August 1982). So far this August the average has been 82.9°. No doubt this will surpass last month as the warmest such on record. The summer has averaged 81.0°, tied with 1996 as the warmest climatological summer. July saw 11 days setting record daily highs and August seven days so far (as of August 25th). On August 22nd the temperature reached 97°, tying the site’s all-time (any month) heat record last observed on August 31, 1994. POR since 1954 for temperature data at the Kuhului airport.
The 97° figure is also quite likely the warmest reliably measured temperature on record for the state of Hawaii. Although temperatures of 98°-100° are in the record books for various sites on seven different occasions (in all), a close look at every one of these readings exposes a lack of credibility. The only way any of these readings could be, in fact, accurate is if some very local and extreme type of downslope wind effect took place confined only to the sites in question and not observed at any other nearby sites. This is very unlikely.
Snow in Hawaii in the middle of one of its hottest summers on record?
The day after Hilo measured a daily record high of 89° on July 16th, a rare July snowfall blanketed the summit (13,796’) of Mauna Kea (just 30 miles away as the crow flies) on July 17th. Hilo saw a daily record rainfall on that day of 2.97” and a temperature range of 71°-84°. Although snowfall on the summit of Mauna Kea (and the other high volcanic peaks of Hawaii) is fairly common, this is the first instance I am aware of a July snowfall. The accumulation was measured at 1.5”. Unfortunately, the summit observatory does not keep track of snowfall events so it is quite possible this was not a unique event for the time of the year. Regardless, when it does snow, it is normally associated with cold ‘Kona’ winter storms that occur between November and April.
Web cam screen shot of the 1.5” of snowfall that blanketed the summit of Mauna Kea on July 17th. I’m not sure how rare snowfall in mid-July is at the summit of the mountain, but it is a strange sight in respect to the record warm temperatures that were occurring at lower elevations. Image courtesy of Mauna Kea Observatory.
Christopher C. Burt
Weather Historian
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