Weather Forecast

Hawaii County Weather Forecast for October 17, 2021

October 17, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Mostly cloudy with showers likely. Highs 76 to 82 near the shore to around 68 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows around 67 near the shore to around 53 at 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs 78 to 84 near the shore to around 69 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 80 to 85 near the shore to around 70 near 5000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 69 to 75 near the shore to around 54 near 5000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 20 percent.

ARTICLE CONTINUES BELOW AD

Monday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 71 near 5000 feet. West winds up to 10 mph. Chance of rain 30 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs around 78 near the shore to 70 to 77 near 3000 feet. East winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 66 near the shore to 54 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs around 78 near the shore to 70 to 77 near 3000 feet. East winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 66 near the shore to 54 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

South Big Island

Today: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 81 near the shore to around 70 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 66 to 71 near the shore to around 52 near 5000 feet. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 82 near the shore to around 72 near 5000 feet. East winds 10 to 20 mph decreasing to up to 15 mph in the afternoon. Chance of rain 30 percent.

Puna

Today: Mostly cloudy with showers likely. Highs 76 to 82 near the shore to around 68 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows around 67 near the shore to around 53 at 4000 feet. Southeast winds up to 15 mph. Chance of rain 70 percent.

Monday: Partly sunny with scattered showers. Highs 78 to 84 near the shore to around 69 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 79 to 85 near the shore to 67 to 73 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 72 near the shore to 50 to 59 above 4000 feet. Southeast winds up to 20 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 80 to 86 near the shore to 68 to 74 above 4000 feet. North winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Detailed Forecast

Synopsis

High clouds will continue to spread across the area, and bring partly to mostly cloudy skies over the state today. The breezy trade winds will persist with passing showers favoring windward and mauka areas through tonight. Expect a weakening trend in trade wind speeds and a drier weather pattern from Monday into mid- week. The trade winds may strengthen and bring increasing cloud cover and showers later this week.

Discussion

A 1028 mb surface high pressure system is centered near 38N 148W, or more than 1300 miles northeast of Honolulu. There is also a nearly east to west oriented monsoon trough in the deep tropics about 600 miles south of South Point on the Big Island. Hawaii remains sandwiched in the tight pressure gradient between these two features. As a result, breezy trade winds persist across the area early this morning. Aloft, a mid-tropospheric area of low pressure is evident just north of the state. The close proximity of this feature is causing some atmospheric instability across the islands, which has weakened the low-level trade wind inversion. Satellite imagery shows large areas of mid- and upper- level clouds moving across most of the state, especially over Kauai and the Big Island. Radar reflectivity data shows isolated showers moving into the windward sides of the eastern islands.
The forecast guidance indicates these high clouds will continue to spread across most of the state this morning. This is in response to an upper-level trough that is shifting down from the north toward the region. This will likely bring mostly cloudy skies across Kauai and the Big Island, with partly to mostly cloudy conditions elsewhere across Oahu and Maui County today. The guidance also keeps the breezy trade winds in place through tonight. The slight instability may produce some localized enhancement in low clouds and showers, especially over windward Kauai during the night and early morning hours. However, the main focus of near normal precipitation will likely remain over windward and mauka areas of the islands east of Kauai during the next 18 to 24 hours.
As the area of the low pressure aloft eventually moves west of the state on Monday, the atmosphere will likely become more stable. The surface high pressure north of the state is also forecast to weaken as it moves south from Monday through Wednesday. This is expected to cause the trade winds to gradually weaken and shift from a more northerly direction through Tuesday. The background flow may become even lighter from the north to northeast by Wednesday. At the same time, expect low clouds and showers to also decrease, with mainly brief showers from time to time over some north to northeast sections. Daytime sea breezes will be possible over leeward areas starting Tuesday, which could bring some brief showers over leeward and interior sections of some of the islands each afternoon.
Starting Thursday, the forecast guidance indicates surface high pressure will build far north of the state. This is expected to push low clouds and showers along a remnant frontal boundary down towards the state from the north. The models appear to be less certain about whether these clouds and showers will reach the state, with the ECMWF trending toward keeping the bulk of the moisture along the boundary north of the islands east of Kauai. It does appear that the trade winds may eventually strengthen starting late Thursday.

Aviation

High pressure north of the islands will keep moderate to locally breezy trade winds in place through tonight. Low clouds and showers will mainly affect windward and mauka areas, particularly during the overnight and early morning hours. A stray shower may spill over into leeward communities, but most leeward areas will remain dry.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the terrain of all islands. This AIRMET is expected to remain in effect through the day.

Marine

A series of fronts passing north of the islands will weaken the ridge and subsequently the trade winds in the coming days, trending the winds down to moderate range by Monday. The Small Craft Advisory (SCA) has been extended out to 6 am HST Monday morning for the typical windy waters of Maui County and waters south of the Big Island.
The trades are slated to become light northeast Wednesday, while a front falls apart north of the islands. High pressure settling in north of the islands will be bringing back moderate to strong trades on Friday.
With trade winds trending down in the coming days, so will the locally generated trade wind swell. So expect lowering surf along the east facing shores through at least Monday. Surf will likely rise again over the upcoming weekend due to the strengthening trades.
There will be a series of north-northwest and north swells arriving this week. The first swell, a small pulse from the north- northwest is expected to arrive Monday. This swell will be reinforced by a slightly bigger north- northwest swell Tuesday night into Wednesday. Then, on Friday, a larger north swell arrives, where the surf may reach advisory level along the north facing shores. Small pulses from the southeast and south will maintain small surf along the south facing shores well into next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov

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