Comparing Hawaii'sTropical Storm Lala to Washington’s December floods

Hawaii recently experienced devastating flooding from Tropical Storm Lala. So how does it compare with our atmospheric river flooding in Washington last December?

Turns out, there are some interesting similarities. First, both storm systems were fueled by deep Pacific moisture. And both dumped tremendous amounts of rain over mountainous terrain, sending huge volumes of runoff into rivers, streams, and valleys below.

Both events also produced extraordinary rainfall totals measured in feet, not just inches.

But Hawaii's recent flooding was even more concentrated. Laupahoehoe on the Big Island recorded 43.54 inches of rain from Lala, with most of that rain falling over just a few days.

Western Washington's flooding, meanwhile, developed during a much longer series of storms in December. The most intense atmospheric river hit December 8 through 11, when some mountain communities picked up 20" of rain. The broader storm pattern continued to keep the region exceptionally wet through much of the month.

Another big difference was the engine driving all that rain.

Washington's flooding was fueled by an atmospheric river—a long, narrow corridor transporting enormous amounts of water vapor across the Pacific and repeatedly directing it into the Pacific Northwest.

Hawaii's flooding came from a tropical cyclone—an organized storm powered by warm ocean water, producing intense bands of tropical rainfall along its path.

So both storms had a similar ingredient—an enormous supply of Pacific moisture—but delivered it differently: Washington's was the prolonged atmospheric-river event; Hawaii's was the shorter, more concentrated tropical deluge.