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Hawaii Island Weather Outlook for January 22nd, 2021

Wind Advisory has been issued for parts of the Island of Hawaii through Sunday morning (January 24th).

Wet weather (with the possibility of widespread heavy rains) possible for the Island of Hawaii from Sunday to Monday (January 25th).

(Further details for both advisory and outlook/forecast posted below)

Published by: HIRSC - Weather Team



* WHAT...East winds 20 to 30 mph with localized gusts over 45 mph
  expected. Winds will be strongest over and immediately downwind
  of the mountains.

* WHERE...Portions of Kauai, Oahu, Molokai, Lanai, Maui and the
  Big Island.

* WHEN...Until 6 AM HST Sunday.

* IMPACTS...Winds this strong are capable of downing tents or
  other temporary structures, as well as downing trees and
  causing power outages.


Motorists should use extra caution.

Hydrological Outlook for the State of Hawai'i as of 9:00 pm Friday evening:


A very strong surface high will develop far northeast of the islands
this weekend, while a low develops far to the northwest. Strong
trade winds are expected to bring brief and passing windward showers
through most of the weekend, but the strong winds are expected to
shift to the southeast Sunday and Monday, bringing increased
moisture over the islands.

A slow-moving convergence band is expected to develop, bringing the
threat of several days of widespread rainfall, with locally heavy
showers possible. This band could lead to the development of
training rainfall over the islands, where showers repeatedly form
over the same area, potentially leading to flash flooding.

While it is too early to provide specifics as to where and when the
heaviest rain will occur, there is increasing confidence that
widespread heavy rain will affect at least portions of the islands
from late Sunday into the middle of next week.

Keep up to date with the latest forecast information through the
Internet (weather.gov/hawaii), local media, social media, or NOAA
Weather Radio broadcasts. An updated Hydrologic Outlook will be
issued by 5 AM HST Saturday.


Hawaii Forecast Discussion as of 8:40 pm Friday evening:


Strong and gusty trade winds will become especially strong over the weekend, delivering passing clouds and showers, some briefly heavy, mainly dampening windward areas. More widespread rainfall may develop early next week as winds remain strong and shift to the southeast.


Windy and locally wet trade wind weather will prevail through the weekend, with most clouds and showers focused over windward areas. The strong trades will blow showers leeward on the smaller islands, leading to prime rainbow weather as leeward areas should see ample amounts of sunshine. Strong winds will shift to the southeast early next week, increasing the potential for widespread cloudiness and rainfall starting on Sunday over the Big Island, spreading to the other islands Monday and Tuesday, then diminishing after mid-week. A Flood Potential Outlook (ESFHFO) has been issued to bring attention to the potential for widespread rainfall. After a relatively dry day statewide, satellite and radar data show an increased amount of showery and stable low clouds immediately upstream of the islands from Maui to Kauai, being driven quickly westward by a 1034 mb surface high centered to the distant NE. Low- level moisture extends as high as 10 thousand feet, due to the presence of weak troughing in the mid- and upper-levels, which has led to a weakened subsidence inversion. This will lead to an increase in overnight showers, mainly windward. While fewer clouds lie upstream of the Big Island, orographic forcing will likely drive the formation of a few showers over the windward slopes. Meanwhile, most leeward communities will remain mostly dry. Through the weekend, mid-level temperatures will remain cooler than normal, and strong trade winds will strengthen as the high to the distant NE is reinforced Saturday and Sunday, reaching a central pressure over 1040 mb. A Wind Advisory is in effect for a large portion of the area in anticipation of the strengthening winds. The development of a deep-layer low to the distant W and NW of the islands is expected to cause the winds to veer to the SE late in the weekend, while an associated moisture convergence band extending SE from the low creeps towards the islands from the S. Latest guidance indicates this band will move over portions of the islands from late Sunday into Wednesday - bringing PWAT close to 2", layered cloudiness, and widespread rainfall. Deep moisture and modest instability are expected, so the chance of thunderstorms appears too low to mention thus far. A drying trend is generally expected thereafter as the band shifts W of the area. High pressure to the distant NE will continue to support locally strong trade winds.

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