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Hawaii Island Weather Update for January 17th, 2021

A Flash Flood Watch has been issued for the Island of Hawaii from Monday morning (January 18th) till Tuesday evening (January 19th). Snowfall atop the summits of Maunakea and Mauna Loa is possible over the next few days.

Published by: HIRSC - Weather Team


The National Weather Service in Honolulu has expanded the

* Flash Flood Watch to include the Big Island.

* From Monday morning through Tuesday afternoon

* A cold front will move over the islands from the northwest
  tonight, then stall near Maui and the Big Island Monday through
  Tuesday. A low aloft combined with strong north and northeast
  winds will help enhance precipitation along windward and mountain
  areas. These areas especially around the Hamauka coast will see
  the greatest risk for 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 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.

Hawaii Forecast Outlook as of 4:00 pm Sunday afternoon from NWS:


A vigorous front will move down the island chain tonight, then stall around Maui and the Big Island between Monday and Tuesday. Behind the front, we will see strong northerly winds of 20 to 30 mph with stronger gusts. The combination of strong northerly winds, and an upper level low aloft, will bring the risk of Flash Flooding to parts of Oahu, Maui County and the Big Island. The greatest risk will be along windward and mountain areas, especially on Maui Monday afternoon and Monday night. Moderate to strong easterly trade winds return to the region during the second half of the week with a bit of a wet flavor.


The leading edge of a vigorous cold front is now moving through Kauai and is expected to move through Oahu and Maui County later tonight. Numerous impacts are expected with this front, including the potential of flash flooding and strong northerly winds behind the front. A Flash Flood Watch has been expanded to include the Big Island with this forecast package. Confidence is increasing for flash flooding Monday into Monday night especially around windward areas of Maui County and the Big Island. The latest model guidance is in fairly good agreement with the front stalling between Maui and the Big Island on Monday. The combination of the strong northerly winds and an upper level low aloft will enhance precipitation and will allow rainfall to anchor over the terrain. Confidence is increasing for select areas to receive over 10 inches of rainfall during this event. The most likely areas to see heavy rain will be over windward Maui and the Hamakua Coast on the Big Island between Monday afternoon and Monday night. Also due to the strong northerly winds expected behind the front, a Wind Advisory has been issued for the smaller islands with sustained winds of 20 to 30 mph with gusts of over 45 mph expected. Although the front looks to dissipate on Tuesday, moisture associated with the front will continue to linger across the state and is expected to slowly drift westward through Wednesday. The strong northerly winds should taper off by then, and breezy trades should return by the middle of the week. A trade wind pattern is expected for the second half of the week but due to lingering moisture, we will likely see a more of a wet trade wind pattern.


Maunakea and Mauna Loa Summits Forecast as of 6:00 pm Sunday evening (January 17th)

Mauna Loa Weather Forecast through Thursday, January 21st.
Maunakea Weather Forecast through Thursday, January 21st.

Based on the latest weather models/forecast reviewed, the heaviest snowfall is expected to happen on Monday afternoon and continue through Tuesday morning on both summits. From Tuesday Evening through Thursday morning, a light dusting of snow is possible.

Maunakea Access Road information as of 6:00 pm Sunday evening:


The access road to the summit of Maunakea is closed overnight to the public at the Visitor Information Station located at the 9,200 feet elevation due to a forecast for high humidity and below-freezing temperatures. There is a risk of increasing fog with ice and flurries overnight.

The Maunakea Rangers will continue to monitor the summit weather conditions and update this message accordingly.

Thank you for your patience and understanding.

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