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Hawaii Island Flood Watch Update for March 12th, 2021

A Flash Flood Watch for Hawaii Island has been extended until Saturday evening (March 13th). The potential for more moderate to heavy showers is likely beginning early Saturday morning for the West Hawaii districts of Hawaii Island.

Published by: HIRSC - Weather Team


The Flash Flood Watch is now in effect for

* The Big Island.

* Through Saturday afternoon

* A front over the western half of the state, along with a moist and
  unstable atmosphere will maintain the potential for intense
  rainfall and flash flooding.

* Significant flooding may occur due to the overflow of streams and
  drainages. Roads in several areas may be closed, along with
  property damage in urban or low lying spots due to runoff.
  Landslides may occur in areas with steep terrain.


Be prepared to take action if a Flash Flood Warning is issued. If
you experience heavy rain or rising waters, head to higher ground

A Flash Flood Watch means that conditions are favorable for flash
flooding. Flash Flooding is LIFE THREATENING. Do not cross fast
flowing water in your vehicle or on foot.


The wet pattern will continue as a front and upper disturbance advance down the island chain overnight through Saturday. Heavy showers and a few storms along and ahead of the front combined with saturated grounds will keep the threat for localized flash flooding in place across the state. Brisk trade winds will follow the front, which will focus clouds and showers over windward and mountain locations. The wet pattern will be possible through the first half of the upcoming week as low pressure tracks westward across the state.


Heavy showers and a few thunderstorms will continue to belt portions of the state as a cold front and upper trough advance down the island chain overnight through Saturday. This additional rainfall will only aggravate the ongoing flooding issues due to the inundated soils and swollen streams from the week's heavy rainfall. Although the rainfall will become more widespread over the eastern end of the state late tonight through Saturday as this front moves through, strong north to northeast winds following its passage will shift the rainfall coverage to windward and mountain locations for Kauai and Oahu through this time. This has already begun this evening on Kauai in the wake of this boundary, where gusty northerly winds and showery conditions (rainfall rates ranging from a quarter to half of an inch per hour) continue to impact the northern slopes. In addition to the rainfall, the gusty winds filling in behind the front over the western end of the state combined with the saturated soils could translate to downed trees tonight through Saturday, which could further delay or impact restoration efforts. As a result, the Flash Flood Watch remains in effect statewide through Saturday and a wind advisory for Kauai will be possible later tonight. For the Big Island Summits, gusty winds along with a wintry mix can be anticipated overnight through Saturday as the aforementioned shortwave trough dives southeastward into the area. The Winter Weather Advisory for the Summits may need to be extended into Saturday night in later packages. Despite the model inconsistencies this week that has lowered forecast confidence for later this weekend and next week, the last two model cycles between the various solutions have been more consistent and in decent agreement. They depict low pressure positioned northeast of the state along the front beginning to track back toward the islands Sunday, then through the islands as a trough early next week. If this solution evolves as projected, expect gusty northerly winds to hold over the western end of the state and potentially remaining light over the eastern end. This surface feature combined with broad upper troughing over the region will keep the rainfall chances in the forecast. They indicate the low opening and dampening out as it slips west- southwest of the area with trades returning statewide Wednesday.

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