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Hawaii Island Weather Update for January 18th, 2021

A Flash Flood Watch remains in effect for Hawaii Island till Tuesday evening (January 19th) and Winter Weather Advisory remains in effect for the summits of Maunakea and Mauna Loa until Tuesday morning.

Drier conditions along with breezy trade winds are expected to take over beginning Tuesday afternoon.

Published by: HIRSC - Weather Team

Flash Flood Watch Update for January 19th, 2021 at 11:00 pm:


The Flash Flood Watch continues for

* The Big Island.

* Through Tuesday afternoon

* Abundant moisture from a stalled front near the Big Island will
  continue to bring the threat of flash flooding through Tuesday.
  The greatest areas of risk will be over windward and mountain
  areas. This moisture will gradually shift westward on Tuesday and
  the threat of flash flooding should gradually decrease on the Big

* 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 also 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.
Gemini Telescope Webcam - Facing West

Winter Weather Advisory for the Summits of Maunakea and Mauna Loa Update as of 11:00 pm:


* WHAT...Snow expected. Total snow accumulations of 2 to 4

* WHERE...Big Island Summits above 12,000 feet.

* WHEN...Through 6 AM HST Tuesday.

* IMPACTS...Plan on slippery icy road conditions and low
  visibility in freezing fog.


A Winter Weather Advisory means that periods of snow, sleet, or
freezing rain will cause travel difficulties. Be prepared for
slippery roads and limited visibilities and use caution while

Hawaii Forecast Discussion as of 8:52 pm Monday evening:


A large cold front stalled out over Maui and the Big Island this evening will continue to produce widespread rain across the eastern islands through Tuesday. This unstable cloud band begins to drift westward on Tuesday with shower trends increasing over the western islands of Oahu and Kauai through Tuesday night. Strong north to northeasterly winds will begin to ease over the eastern islands by early Tuesday morning, becoming moderate to breezy trade winds for Maui and Hawaii Counties. Windy and wet weather conditions will continue over Oahu and Kauai through Tuesday afternoon. Improving weather trends are forecast from Wednesday through the end of the week with moderate to breezy easterly trade winds with periods of showers favoring windward and mountain areas. Trade winds are expected to strengthen through the weekend with more scattered shower activity.


A Flash Flood Watch remains in effect for all islands between Oahu and the Big Island through Tuesday afternoon due to a large diminishing cold front and strong northerly winds elevating regional flash flood threats. Unstable moist air along this frontal cloud band will be forced up the windward and mountain slopes of each island producing widespread rain, heavy at times. The highest rainfall amounts are expected to fall along the northern to northeastern slopes of each island due to orographic forcing. Enough dynamic forcing and instability over the region may produce a few thunderstorms along this frontal cloud band. A Winter Weather Advisory remains in effect for the highest peaks on the Big Island above 12,000 feet elevation, where 2 to 4 inches of total snow accumulations are forecast through Tuesday morning. On Tuesday, a high pressure ridge building north of the Hawaiian Islands will begin to shift towards a more easterly direction. The cold frontal band will diminish into a trough as this unstable cloud band is pushed back westward with increasing rainfall trends for Oahu and Kauai through Tuesday evening. Meanwhile out east, the Big Island and Maui will begin to see improving weather trends by Tuesday afternoon with gradually decreasing rainfall amounts. Wind speeds over these eastern islands will weaken by Tuesday morning. A wind advisory remains in effect for all islands through Tuesday morning, this advisory may be extended for Oahu and Kauai through Tuesday afternoon. Wednesday through Friday, this wet and windy weather pattern will diminish by Wednesday. Wind and flood threats will diminish as the trough fades and drifts west of the islands. Trade winds will become moderate to breezy easterlies with periods of showers favoring windward and mountain areas, less showers are forecast over leeward areas. Saturday and Sunday, trade winds will increase through the weekend, becoming breezy to windy easterlies on Sunday. Isolated to scattered showers remain in the forecast for both days favoring typical windward and mountain areas.

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