Weather Forecast

Hawaii County Weather Forecast for October 18, 2021

October 18, 2021, 7:15 AM HST
Listen to this Article
5 minutes
Loading Audio...
A
A
A

no slideshow

Hilo

Today: Partly sunny with scattered showers. Highs 78 to 84 near the shore to around 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 66 near the shore to around 52 at 4000 feet. Northeast winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 84 near the shore to around 69 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated 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 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows 69 to 74 near the shore to around 54 near 5000 feet. Light winds.

ARTICLE CONTINUES BELOW AD

Tuesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 86 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs around 80 near the shore to 71 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 65 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Tuesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs around 80 near the shore to 71 to 78 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 65 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 40 percent.

Tuesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds up to 15 mph shifting to the northeast 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 83 near the shore to around 72 near 5000 feet. Northeast winds up to 20 mph shifting to the east 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows around 66 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph decreasing to up to 10 mph after midnight.

Tuesday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 82 near the shore to around 72 near 5000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Puna

Today: Partly sunny with scattered showers. Highs 78 to 84 near the shore to around 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 66 near the shore to around 52 at 4000 feet. Northeast winds 10 to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 78 to 84 near the shore to around 69 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny. Highs 81 to 86 near the shore to 68 to 74 above 4000 feet. North winds up to 10 mph.

Tonight: Mostly clear. Lows around 71 near the shore to 51 to 58 above 4000 feet. Southeast winds up to 15 mph.

Tuesday: Sunny. Highs 80 to 86 near the shore to 67 to 74 above 4000 feet. North winds up to 10 mph in the morning becoming light.

Detailed Forecast

Synopsis

The locally breezy trade winds will continue to transport low clouds and brief showers across windward and mauka areas today. The high clouds will gradually decrease in coverage near Kauai as upper-level low pressure west of the state moves away. Weakening trade winds and a drier weather pattern are expected from later today and tonight into mid-week. The trade winds are forecast to strengthen again starting late Thursday or Friday. Windward showers may also increase over some islands later this week.

Discussion

A nearly east to west oriented subtropical ridge is evident about 600 miles due north of Honolulu. A surface trough in the deep tropics appears to be about 550 miles south-southeast of South Point on the Big Island. The islands remain sandwiched between these two features, which is maintaining the relatively tight pressure gradient across the region. As a result, gusty trade winds persist over most of the island chain, especially around the Big Island.
Aloft, mid- and upper-level low pressure systems are centered nearly 550 miles west-northwest of Lihue. As these stacked areas of low pressure continue moving westward, the atmosphere is gradually stabilizing this morning. The low-level trade wind inversion is beginning to become established again based on the early morning sounding profiles from Lihue and Hilo. Loops of infrared satellite imagery indicate the coverage of cirrus clouds along the southeastern flank of the low pressure aloft has also decreased overnight. Some cirrus will likely persist over portions of the island chain (especially Kauai) into this afternoon. Radar reflectivities show isolated to locally scattered showers moving into the windward sections of some of the islands.
The high resolution forecast guidance indicates the breezy trade winds will likely persist into this afternoon. As the upper trough continues moving west of the state, expect increasing stability to develop across the area. At the same time, the surface ridge north of the state will likely weaken as it moves southward from tonight through Wednesday. The background flow is forecast to also be from a northeast direction from tonight into mid-week. Expect less low clouds and fewer trade showers, as well as decrease in the coverage of the high clouds tonight.
The background flow is forecast to be weak enough Tuesday and Wednesday to allow an alternating pattern of local afternoon sea breeze and nighttime land breeze circulations to develop. This may allow clouds and isolated showers to form over some interior and leeward sections of the island chain each afternoon. At night, most of the clouds and showers will likely dissipate as the land breezes develop, In addition, brief light showers may move into the northeast sections of some of the islands, especially late at night.
Looking ahead to Thursday, the forecast models continue to depict surface high pressure building far north of the state. This will likely push a diffuse band of low clouds and showers associated with a remnant frontal boundary down towards the state. The recent runs of the forecast models appear to be in some agreement that some of the clouds and showers in the band may reach Kauai. However, the ECMWF continues to keep the bulk of the moisture just north of the islands east of Kauai. For the moment, the latest forecast continues to indicate low clouds and showers will increase over most windward sections of the smaller islands from Thursday into Friday. The models also remain in general agreement that the trade winds will eventually strengthen starting late Thursday, with locally breezy trades potentially returning on Friday.

Aviation

High pressure north of the islands will keep moderate trade winds in place today, with the trades expected to trend lower tonight. Low clouds and showers will bring brief MVFR cigs and vsbys to windward and mauka areas, mainly during the overnight and early morning hours. A stray shower may also spill over into leeward communities, but most leeward areas will remain dry. Overall, predominantly VFR conditions should prevail at the TAF sites during the next 24 hours.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the terrain of all islands. This AIRMET will likely be lowered at some point later today.

Marine

The moderate to locally strong trade winds will be trending down to moderate speeds by this evening. The overnight ASCAT pass revealed the locally strong trades hanging tough, thus the Small Craft Advisory (SCA) has been extended until 6 pm HST today. The cause of the lighter trades is the ridge north of the islands being weakened by a series of fronts from storm systems over the far northeast Pacific. A front or two will make its way into the northern offshore waters this Wednesday and Thursday, where both fronts are expected to fall apart before reaching the Hawaiian Islands. High pressure reestablishes north of the islands Thursday through Friday, resulting in a boost in the trades to locally strong levels for select waters around Maui County and the Big Island, as well as the issuance of a SCA.
As the trade winds ease, the surf along the east facing shores will be lowering a little each day as well. Today’s surf will be similar to Sunday, but will be on a decline each day for the next couple of days. The boost in the trades on Friday will lead to increasing surf along the east facing shores over the upcoming weekend.
We are expecting a series of north-northwest to north swells this week, with the first of three due in today. This small pulse will be reinforced by a slightly larger north-northwest swell Tuesday night through Wednesday. A larger north swell follows in on Thursday night and Friday, where surf is likely to reach advisory levels for the north facing shores. Also, Kahului Harbor and other north facing harbors will be susceptible to moderate harbor surges from this north swell. A Marine Weather Statement addressing this will likely be issued prior to the event. A gradual lowering of this swell will occur over the weekend.
A series of small to moderate northwest to north-northwest swells will take up the first half of next week. Surf along the south facing shores will be small into next week. There is a long 14 to 15 second period south swell due in tonight, lasting through Wednesday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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.