(BIVN) – The Flood Watch for Hawaiʻi begins Wednesday evening, and a Winter Storm Watch has been added for the summits of Maunakea and Mauna Loa, as a powerful and slow-moving kona low moves over the islands from the northwest. 

“Considerable flash flooding is possible beginning later today as a large and powerful kona storm northwest of the state draws deep tropical moisture northward across the islands,” the National Weather Service wrote, concerning Hawaiʻi island. “Persistent bands of heavy rain and thunderstorms may produce intense rainfall rates, leading to rapid rises in streams and flooding of roads and low-lying areas.”

The Flood Watch is expected to be in place for the Big Island from Wednesday evening through Saturday afternoon.

Heavy rain is already impacting Kauaʻi and Oʻahu.

The same weather system is expected to bring heavy snow to the Hawaiʻi island summits, where snow accumulations up to 8 inches is possible.

A High Wind Watch will also be in place at the summits of Maunakea and Mauna Loa from Thursday evening through Sunday afternoon. “Southwest winds 45 to 65 mph will strengthen to 60 to 80 mph by Saturday,” forecasters say. “Wind gusts could exceed 100 mph by Saturday.”

From the National Weather Service discussion posted on Wednesday morning:

In addition to the rainfall threat, strengthening south to southwest winds may develop Friday into the weekend as the pressure gradient tightens between the developing low to the northwest and high pressure to the northeast. If this materializes, strong and potentially damaging kona winds will be possible, including localized downslope winds capable of downing trees and power lines.

Environmental conditions will also periodically become favorable for strong to severe thunderstorms over the next few days, particularly Friday into Saturday. Instability combined with strong deep-layer wind shear during this period will support thunderstorms capable of producing damaging winds, large hail, and possibly a tornado.