Hawaii Flood Threat Expected This Week

Hawaii is going to see yet another round of very heavy rainfall this week.

The entire state is under flood watches as rounds of powerful bands of rain are expected beginning Wednesday and lasting until Friday.

This comes after the state just saw powerful rainfall that caused devastating flooding in March. Flooding from one of these storms led to evacuations of thousands and caused risks of dam failure at the Wahiawa Dam. Back-to-Back Kona lows brought an estimated $1 Billion in damage to the state.

(MORE: March Kona Low Recap)

Happening Now

The first round of heavy rainfall has moved to hit the more eastern islands of the state. Water has been reported over the Hana Highway on Maui by emergency managers, and water was reported coming into a home in the Puna district near Hawaiian Paradise Park on the Big Island.

The heaviest rainfall has been reported across the eastern side of the Big Island, where flash flood warnings are still in place. Rainfall totals over the last 24 hours have widely been between 2-6 inches for the island, with isolated totals topping 6 inches. Heavy rainbands are producing strong rainfall rates, which could lead to more flash flooding.

How Much Rainfall?

Rainfall is expected to surge across the entire island Wednesday to Friday.

Rainfall totals are expected to be highest across The Big Island and Kauai, where storm totals up to 8 inches are possible. However, across higher elevations, rainfall could exceed a foot.

(WATCH: Hawaii Hit With Worst Flooding In Past 20 Years)

And these places are saturated, so it will not take as much to see flooding. Honolulu, for example, has seen over a foot of rainfall since March 1, which is about six times more than its average. And Kahului is even more impressive. It has seen over 20 inches since March 1 and is running about a foot and a half above normal.

Snowfall is possible across the peaks of the highest volcanoes. Across the summits of The Big Island, snowfall up to 6 inches and ice up to a quarter of an inch is possible.

Winds could blow between 40 and 50 mph, with gusts to 60 mph possible across the lee side of the mountains on the islands of Kauai and Oahu.

Cause Of Rainfall

There are a couple of factors in play that are causing this rainfall.

The first is occurring further up in the atmosphere. We have an upper level low pressure system that will pull in moisture from the southwest, spreading it over the state.

Eventually, a surface level low pressure system will develop west of the islands and will enhance that surge of moisture from the southwest. A wide plume of moisture dwells to the southwest of Hawaii, so long story short, when the winds come in from the southwest, you can see some heavy rainfall on the Kona, or western sides, of the islands.

Kona Low?

When you hear about low pressure systems impacting Hawaii, you may have heard the term Kona Low. While this low is meeting the criteria of a Kona Low, it is not the sole driver of the powerful rainfall for the state this time.

(MORE: Weather Words: Kona Low)

But, know this: Whether we call it a Kona Low or not doesn’t diminish the fact that rainfall is coming and will last for days.

The impacts are what are important, and the flood threat for the already waterlogged state is very real.

Rob Shackelford is a meteorologist and climate scientist at weather.com. He received his undergraduate and master’s degrees from the University of Georgia studying meteorology and experimenting with alternative hurricane forecasting tools.