Hawaii County climate forecast is March 18, 2021

March 18, 2021, 7:16 a.m. HST

Hilo

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Kona

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Waimea

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Kohala

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South Big Island

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Waikoloa

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Summary

Breezy to locally windy trades will still carry clouds and showers in windy and mountainous regions today, with some heavier showers reaching the interior and leeward sections of each island. Additional moisture entering the state from the north will help improve the showers through Friday. Strong and gusty trade winds will persist through the weekend, and transient showers will develop throughout the region. Light and changing winds develop from late Monday in an unclear weather regime.

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A high pressure system that runs eastward far north of the Hawaiian Islands will keep windy to locally windy trade winds in the forecast for the weekend. Satellite imagery this morning shows a short-wave upper plain trough moving from the northwest into the state, while the remainder of the cloud band is moving from an ancient front into the islands from the north. Both functions combine forecasts to improve shower activity on all islands by Saturday. Strong trade winds will drive these unstable clouds up the north and east slopes of each island, with coverage and rainfall favoring wind and mountain areas. A subtropical jet lingers over the southern half of the Big Island, creating scattered high cirrus clouds mainly over the Ka’u and Puna districts.
Choppy stormy trade winds will continue this weekend as the upper trough stands over the islands and potentially forms a closed upper low. This upper low increases the instability of passing commercial showers with the possibility of isolated thunderstorms near the islands. Strong trade winds will peak on Saturday, with a slightly declining trend forecast that will begin late Sunday.
Trade wind speeds will be lower from Sunday evening through Monday as the high pressure system drifts further from the main Hawaiian islands into the Eastern Pacific. A low pressure system approaching the islands from the northwest appears to be stalling north of the region. These low pressure systems are likely to generate light and changing winds across the region for an extended period starting Tuesday. Without large winds, land and sea breezes develop on a local scale on every island. Long-range model solutions show that on Wednesday and Thursday a surface trough will move to the western islands, with shower trends increasing along the trough axis. Slow, unstable shower activities and possible thunderstorms can increase the risk of flash floods during this period. However, this forecast for long-term forecasting may struggle a little with the intensity and timing of this next weather system. Stay tuned for updates to our long-term forecast, as these weather effects are likely to change over time.

aviation

Windy trade winds continue to carry clouds and showers towards the windward slopes and coasts. A top trough that runs slowly over the area improves shower activity. Short MVFR conditions are expected in showers on both the windward and leeward coasts. Darkening the mountains remains a possibility for all islands day and night.
A light sea breeze will develop along the lee coast of the Big Island this afternoon. This will initiate the remediation of cumulus accumulations in the interior of the island. Both the sea breeze and the inland showers last into the early evening.
AIRMET Sierra is now in effect for mountain concealment toward the north slopes of Kauai. These conditions can later spread to the rest of the smaller islands.
AIRMET Tango remains effective for both low and high level turbulence. The minor mechanical turbulence above and downstream of high ground from Kauai to Maui is expected to persist for twenty-four hours and possibly beyond. High-level turbulence associated with an airborne jet is currently affecting the Big Island and adjacent waters above FL270, but is expected to end in the morning.

marine

A strong north of the area generates fresh to strong trade winds. A Small Craft Advisory (SCA) applies to all coastal waters due to winds of 25 knots or more, seas of 10 feet or more, or both. The SCA runs through Saturday evening, but there may be periods when some areas fall below the SCA thresholds. The winds will reach almost stormy force from Friday evening in the windier areas as a new high builds northeast of the area. The winds will subside next week as a front approaches from the northwest.
A High Surf Advisory (HSA) is valid for east coasts until Saturday afternoon due to a north swell and strong trade winds. A small north-westerly swell is expected on Monday evening. A large north-westerly swell is possible next Wednesday. The surf will remain low on the south-facing banks until early next week. Waves from storms near New Zealand may cause a slight surge in surf on the south-facing shores starting mid-next week.

HFO watches / warnings / notices

High Surf Advisory until 6:00 p.m. HST Saturday for east facing coastlines of Kauai, Oahu, Molokai, Maui, and the Big Island.
Small Craft Advisory until 6:00 p.m. HST Saturday for all Hawaiian waters,

Data courtesy of NOAA.gov

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