You should not be jealous of folks vacationing in Hawaii this week.
A ferocious Kona Low storm is hitting paradise right now, with very heavy rain, flooding, and high winds. Even blizzard warnings on the peaks on the Big Island.
A Kona Low storm occurs when an area of low pressure builds or moves to a position just west of the islands. In that position, the circulation around the low draws a plume of tropic moisture northward. The Kona Low circulation also causes upward motion that releases the moisture in heavy showers and thundershowers.
Here is a satellite image of atmospheric water vapor taken around 4 PM Sunday. You can see the circulation around the low and an impressive plume of tropic moisture heading northward into the Hawaiian Islands.
Just as in the Pacific Northwest plumes of moisture, the Hawaiian version dumps huge amounts of moisture on the windward (Koʻolau) side of the mountains, with rainshadows on the downslope/leeward (Kona) side of the terrain. The European Center precipitation forecast for the event across the Big Island illustrates the huge variation across the mountainous island.
Now let me show the total precipitation for the 72 hr ending noon today across Hawaii (see below, click on image to expand). Over EIGHT INCHES on the southwest side of the Big Island, but only 1.29 inches near Kona. Similar variations across Maui. It reminds me of the precipitation variation across the Olympic Mountains.
The Hawaiian weather radar image this morning shows the potent Kona moisture band, which was heading westward toward Kuaui. And winds have also been potent, with some exposed locations experiencing gusts to 50 mph. Not my kind of Luau weahter.
The origin of the Kona Low is fascinating, and I will show you a series of upper-level (500 hPa, about 18000 ft) charts to illustrate the evolution. The Kona Low started as a minor trough of low pressure in the westerlies/jet stream that amplified and pushed southward.
In the figures below, the red arrow shows you the low, with the colors indicating higher than normal (red) and lower than normal (blue, purple) heights/pressures.
At 10 PM December 1, it was only a modest trough.
By 4 AM on December 3rd is was a potent trough heading southward.
Relative scary at 4 AM December 5th--and this set up all the bad weather over Hawaii. The central color indicates a VERY, VERY unusual situation.
The good news? The low will slowly drift westward and by Wednesday normal conditions should return, with the northeast trade winds being reestablished. Unfortunately, with so much rain and wind, sediments will obscure the viewing for snorkeling for several days and hiking trails will be muddy.
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Announcements
I will be doing an in-person book signing for the second edition of my book, the Weather of the Pacific Northwest, at the University Book Store in Seattle on Sunday at 1-3 PM. So if you want a signed copy for yourself or a holiday gift....or just to chat...stop in. You can bring a copy if you already possess one or you can purchase a copy there.
And on this Saturday, I will be doing a Virtual Book Talk and Signing, with a talk on Northwest weather and Q&A using Facebook Live at 10 AM. My ability to give live book talks is limited by COVID, so I hope this will serve as a useful substitute. More information on this virtual signing will be coming (all you have to do is go to my Facebook page: https://www.facebook.com/realcliffmass
Better yet....come to the virtual book talk on Saturday and stop in on Sunday.
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