Weather Forecast

Hawaii County Weather Forecast for October 21, 2021

October 21, 2021, 7:15 AM HST
Listen to this Article
5 minutes
Loading Audio...
A
A
A

no slideshow

Photo Credit: James Grenz

Hilo

Today: Mostly sunny with isolated showers. Highs 78 to 83 near the shore to 64 to 70 at 4000 feet. Northeast winds up to 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 62 to 70 near the shore to around 54 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 40 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 40 percent.

Kona

Today: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 68 to 73 near the shore to 48 to 54 near 5000 feet. East winds up to 10 mph.

ARTICLE CONTINUES BELOW AD

Friday: Sunny. Isolated showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. Northeast winds up to 10 mph shifting to the northwest around 10 mph in the afternoon. Chance of rain 20 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with isolated showers. Highs 65 to 84. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 69 near the shore to 54 to 61 near 3000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 66 to 84. East winds 10 to 25 mph. Chance of rain 40 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with isolated showers. Highs 65 to 84. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 62 to 69 near the shore to 54 to 61 near 3000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 66 to 84. East winds 10 to 25 mph. Chance of rain 40 percent.

South Big Island

Today: Mostly sunny. Highs around 83 near the shore to around 65 near 5000 feet. East winds up to 15 mph.

Tonight: Partly cloudy. Breezy. Lows around 71 near the shore to around 51 near 5000 feet. East winds up to 20 mph shifting to the northeast 10 to 15 mph after midnight.

Friday: Sunny and breezy. Highs around 84 near the shore to around 66 near 5000 feet. East winds 10 to 25 mph.

Puna

Today: Mostly sunny with isolated showers. Highs 78 to 83 near the shore to 64 to 70 at 4000 feet. Northeast winds up to 10 mph shifting to the east in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 62 to 70 near the shore to around 54 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 40 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. Northeast winds up to 15 mph shifting to the east in the afternoon. Chance of rain 40 percent.

Waikoloa

Today: Sunny. Highs 81 to 87 near the shore to 65 to 72 above 4000 feet. Northwest winds up to 10 mph.

Tonight: Mostly clear. Lows 69 to 74 near the shore to 49 to 54 above 4000 feet. Southeast winds up to 10 mph.

Friday: Sunny. Highs 82 to 88 near the shore to 66 to 73 above 4000 feet. Northeast winds up to 15 mph shifting to the northwest in the afternoon.

Detailed Forecast

Synopsis

An area of low clouds and light showers is pushing down across most of the smaller islands early this morning. Easterly trade winds will gradually strengthen later today and tonight, which will likely transport additional low clouds and showers into the windward sides of the islands, especially Kauai and Oahu, from tonight through Friday. Expect breezy trade winds from Friday through this weekend. In addition, drier conditions will also return across most of the smaller islands starting Saturday, but showers may increase over the windward Big Island early this weekend. The trade winds are expected to gradually weaken early next week.

Discussion

An area of broken low clouds and light showers continues to push down across portions of the smaller islands early this morning. This is the remnant moisture from a dissipated frontal boundary. There are much fewer clouds and showers to the north of this area of moisture, so it appears that there will be a break in precipitation over many areas some time after sunrise this morning.
The leading edge of a band of broken low clouds and scattered showers associated with a weakening frontal boundary is less than 300 miles north of Lihue. Elsewhere, a 1027 mb surface high pressure system centered near 37N 158W, or about 1100 miles north of Honolulu, is moving toward the south-southeast at 15 to 20 mph. This feature is pushing the frontal boundary down toward the state. The close proximity of the weakening front between the islands and the high to the north continues to produce light background northeasterly flow across most of the state early this morning.
The forecast guidance shows the trade winds will gradually become more easterly and strengthen later today and tonight. These trade winds will likely transport low clouds and showers over windward and mauka sections of the islands, especially Kauai and Oahu, through tonight. A few showers may also reach some leeward sections of the western islands. By Friday, the trade winds will be locally breezy. The models still indicate the relatively wet trade wind weather pattern may continue across windward and mauka areas of the western islands through Friday as the remnant moisture lingers and a weak upper-level trough moves into the vicinity of the state.
The trade winds will likely remain breezy this weekend. At the same time, mid-level ridging builds in, which will eventually strengthen the low-level trade wind inversion. The area of low clouds and showers over the western islands is expected to push west of Kauai. An area of low-level moisture may be transported toward the Big Island from the east by the trades Saturday. The models show this moisture passing south of the rest of the state, so any low clouds and showers within this area would mainly impact the windward and southeastern Big Island. The surface high pressure system to the north may eventually weaken early next week, which could lead to a weakening trend in trade wind speeds by next Tuesday.

Aviation

The overall wind flow remains weak across the state, with land breezes over the more sheltered leeward areas. The remnants of a couple of old fronts remain evident in satellite imagery early this morning, the first of which has reached Kauai and Oahu, providing a slight increase in shower activity and cloud cover. The moisture associated with the second batch will become more diffuse as it nears the islands later today, but should still be enough to increase clouds and showers over windward areas this evening and tonight. Trades will restrengthen later today as well, helping to push a few showers to leeward areas at times.
No AIRMETs are currently in effect, but TEMPO MVFR conditions with mountain obscuration are possible along windward slopes, especially for the western half of the state. Trades will increase further tonight through Friday, which could warrant an AIRMET Tango for moderate low-level turbulence.

Marine

No major changes to the coastal marine forecast this morning, with things pretty much on track. The remnants of a front will bring some clouds and showers mainly to the windward waters, but the organization of this feature is quickly falling apart. Some evidence of this boundary is expected to remain near the islands over the next 24 hours or so.
Behind the front, a new high will will build north of the islands. As the high builds in, expect a gradual increase in northeast trade winds late today/tonight, shifting to the east at moderate to locally strong speeds by Friday. As the winds increase, a Small Craft Advisory (SCA) will be required for the typical windier waters near Maui and the Big Island. It could be as early as tonight, but more likely tomorrow as winds reach SCA levels, with winds expected to remain nearly steady then into next week.
Nearshore buoy observations are generally on track with the current forecast. The current north-northwest swell may still boost surf along exposed shores over the next few hours, but will then diminish into Friday, as a new north swell is expected to build. This next swell is being generated by a powerful low moving into the Gulf of Alaska. While this swell has the potential to bring surf to near advisory levels, confidence remains not so high given the relatively small window for the swell generation. Due to the size and direction of the swell, this has the potential to produce moderate harbor surges in the Kahului and Hilo harbors. A low near the Aleutian Islands will generate a small to moderate northwest swell for Sunday/Monday. A slight increase in long- period south swell is expected today/tonight. As the trades increase over the weekend, expect a slight boost in short-period wind waves along east facing shores.

HFO Watches/Warnings/Advisories

None.

Big Island Now Weather is brought to you by Blue Hawaiian Helicopters.

Check out their Big Island Helicopter Tours today!

Data Courtesy of NOAA.gov

Comments

This comments section is a public community forum for the purpose of free expression. Although Big Island Now encourages respectful communication only, some content may be considered offensive. Please view at your own discretion. View Comments

Newsletters

Get a quick summary of what’s happening on the Big Island with our daily & weekly email of news highlights.