Hawaii Island Weather Update for February 27th, 2021

A Flash Flood Watch for parts of Hawaii Island (mainly East Hawaii districts) remains in effect until Sunday afternoon (February 28th).

Published by: HIRSC - Weather Team



The Flash Flood Watch continues for

* Maui and the Big Island.

* Through Sunday afternoon

* A persistent trough aloft will bring the potential for a
  prolonged period of rainfall to windward portions of Maui and
  the Big Island. Increasing ground saturation from repeated
  heavy rain bands will produce an increasing threat for flash
  flooding through the weekend.

* Flood prone roads and other low lying areas may be closed due
  to elevated runoff and overflowing streams. 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.


Strong and gusty trade winds will continue into early next week, while a trough aloft keeps the island atmosphere unstable. Clouds and showers will focus over windward areas, with some occasional heavy downpours. Increasing moisture near Maui and the Big Island will bring a more widespread threat of heavy windward showers, and a slight chance of thunderstorms. Typical trade wind weather will continue through much of next week, with showers favoring windward and mauka areas and spreading into leeward communities from time to time.


Currently, at the surface, a 1043 mb high is centered around 1600 miles northeast of Honolulu, while another 1033 mb high is centered around 1550 miles northwest of Kauai. In between these two highs, a nearly stationary south-southwest to north-northeast oriented front is located around 950 miles northwest of the Garden Isle. The gradient over the local area remains rather tight this evening, with breezy trade winds prevailing across the entire island chain. Infrared satellite imagery shows partly to mostly cloudy skies in windward areas, and clear to partly cloudy conditions in most leeward locales with the exception of leeward Big Island where mostly cloudy conditions persist. Radar imagery shows scattered to numerous showers moving into windward and mauka areas, with a few showers spreading to leeward areas from time to time. Main short-term concerns revolve around the Flash Flood and Winter Weather headlines, as well as the trade wind trends through the weekend. High-pressure northeast of the state will settle southward and weaken during the next couple of days, while the high northwest of the state builds eastward and strengthens to around 1044-46 mb by late Sunday and Sunday night due north of the island chain. This high will settle southward and weaken slightly early next week, followed by a new 1044 mb high building northwest of the state during the middle to latter part of next week. Overall, breezy to windy trades are expected to continue through the weekend and into early next week, with the trades peaking late Sunday through early Tuesday. Wind Advisories will likely be required once again for portions of the state during this time. The trades should ease a bit for the middle and latter part of next week, but will likely hold at moderate to breezy levels. As for the remaining weather details, the island atmosphere will remain unstable through the weekend and into next week, due to the presence of a persistent trough aloft, and its associated cold pool. As a result, inversion heights will be pretty much eliminated, allowing for heavier showers to affect windward areas and sending showers into leeward communities more regularly as well. While these showers will be progressive and will not linger over any one area for a prolonged time, high-resolution and global model guidance continues to indicate the likelihood of repeated development over the windward slopes of Maui and the Big Island during the next couple days. This persistent rainfall is expected to lead to increasing ground saturation and rising levels in streams and rivers, with additional rainfall potentially resulting in flash flooding as the weekend progresses. As a result, a Flash Flood Watch (FFA) remains in effect for windward portions of Maui and the Big Island. An expansion of the FFA to windward portions of the other islands is not anticipated. The cold temperatures aloft and deeper-than-normal moisture means that the Big Island Summits will receive periods of wintry weather, with the primary threats being freezing rain leading to icy roadways, although snow showers will mix in as well. A Winter Weather Advisory remains in effect through Monday morning and may need to be extended as the trough aloft lingers well into next week.

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