Weather Forecast

Hawaii County Weather Forecast for July 21, 2021

July 21, 2021, 7:16 AM HST
Listen to this Article
5 minutes
Loading Audio...
A
A
A

no slideshow

Hilo

Today: Scattered showers. Partly sunny, with a high near 82. Calm wind becoming east northeast 5 to 9 mph in the morning. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 67. Northeast wind around 6 mph becoming calm. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Thursday: Showers likely, mainly before noon. Partly sunny, with a high near 81. Northeast wind 3 to 8 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Isolated showers after noon. Partly sunny, with a high near 79. West southwest wind 3 to 8 mph. Chance of precipitation is 20%.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 67. East wind 3 to 8 mph. Chance of precipitation is 20%.

ARTICLE CONTINUES BELOW AD

Thursday: Scattered showers after noon. Mostly sunny, with a high near 79. Calm wind becoming west southwest around 6 mph in the morning. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Scattered showers. Mostly cloudy, with a high near 76. Windy, with a northeast wind 18 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 59. Breezy, with a northeast wind around 22 mph, with gusts as high as 31 mph. Chance of precipitation is 50%. New precipitation amounts between a quarter and half of an inch possible.

Thursday: Scattered showers. Partly sunny, with a high near 75. Windy, with a northeast wind 18 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 50%. New precipitation amounts between a quarter and half of an inch possible.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Occasional showers. High near 67. Windy, with an east wind 22 to 30 mph, with gusts as high as 44 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Occasional showers. Low around 54. Windy, with an east wind 28 to 30 mph, with gusts as high as 44 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

Thursday: Occasional showers. High near 66. Windy, with an east wind 25 to 29 mph, with gusts as high as 41 mph. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Isolated showers before noon. Mostly sunny, with a high near 81. Windy, with an east wind 23 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Partly cloudy, with a low around 74. Windy, with an east northeast wind 24 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Thursday: Isolated showers. Mostly sunny, with a high near 80. Windy, with an east wind 25 to 29 mph, with gusts as high as 37 mph. Chance of precipitation is 20%.

Puna

Today: Showers likely, mainly before noon. Mostly cloudy, with a high near 79. Breezy, with a north northeast wind 10 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 65. North wind 10 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Thursday: Showers likely, mainly before noon. Mostly cloudy, with a high near 78. Northeast wind 10 to 13 mph. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.

Waikoloa

Today: Mostly sunny, with a high near 83. Windy, with an east northeast wind 18 to 28 mph, with gusts as high as 40 mph.

Tonight: Partly cloudy, with a low around 68. Breezy, with an east southeast wind 16 to 21 mph, with gusts as high as 29 mph.

Thursday: Sunny, with a high near 83. Breezy, with an east northeast wind 18 to 22 mph, with gusts as high as 31 mph.

Detailed Forecast

Synopsis

Breezy trade winds will focus low clouds and showers over windward and mauka areas into Saturday, especially during the nighttime and early morning hours. A few brief showers may also occur over some leeward sections. More widespread showers are possible over portions of the state starting Saturday night or Sunday.

Discussion

Two 1035 mb surface high pressure systems are centered near 42N 166W and 40N 154W, or about 1430 miles north-northwest of Lihue and 1300 miles north-northeast of Lihue, respectively. The tight pressure gradient to the south of these features is maintaining breezy trade winds across the state early this morning. Aloft, a broad upper tropospheric trough remains west of Kauai. A west- southwest to east-northeast subtropical jet stream is also in the vicinity of the state. This jet is transporting cirrus clouds rapidly across the island chain this morning according to satellite imagery. In addition, satellite imagery and radar reflectivity data show scattered to broken low clouds with embedded scattered showers streaming into the windward sides of most of the islands. A few of these showers are also reaching the leeward sections of some of the smaller islands.
The forecast guidance shows the breezy trade winds continuing through early Thursday morning. The low-level trade wind inversion is expected to weaken slightly, but will generally remain rather flat and suppressed around 6 to 7 thousand feet. The low-level trade wind flow will continue to transport low clouds and showers into windward and mauka sections of the state, especially during the nighttime and early morning hours. The gusty trades will also carry a few brief showers over to some leeward sections of the smaller islands. Clouds and showers will develop each afternoon and linger into the evening hours over portions of the leeward Big Island.
Former Tropical Depression Felicia, which is now a weakening remnant low located about 860 miles east-southeast of Hilo, is moving toward the west-southwest at about 15 mph. As this low pressure area related to former Felicia passes south of the area in a couple of days, the gradient will likely tighten across the state. This is forecast to cause the trade winds to remain breezy toward the end of the current work work. In addition, recent output from the global models continues to indicate that some peripheral moisture in the 800 to 700 mb layer associated with former Felicia may reach portions of the state later this week. Forecast model soundings show that as some of this moisture spreads up over the state, there may also be a slight reduction in mid-level stability. The current forecast indicates that there may be an increase in showers over some windward sections, especially the windward Big Island, from Thursday into Friday.
Looking ahead to the weekend, the remnants of former East Pacific Tropical Cyclone Guillermo are expected to reach the forecast area during the latter half of the upcoming weekend. The consensus of the model guidance appears to show the deepest tropical moisture associated with former Guillermo may pass by just to the north of the state. Since this is more than 4 days from now, there is still a great deal of uncertainty in the weekend forecast. For now, the current forecast shows a slight weakening of trade winds speeds by Sunday. In addition, the forecast is for wet trade wind conditions to develop from Saturday night through Monday morning. No heavy rainfall is in the current forecast for this weekend.

Aviation

A strong high pressure ridge north of the Hawaiian Islands will continue to produce breezy trade winds across the region for at least the next few days. Expect passing showers mainly over windward and mountain areas of each island with brief periods of MVFR conditions favoring the overnight to early morning hours. Less cloud coverage and showers are forecast over leeward areas of each island. Wind speeds this strong will also produce Moderate Turbulence over and immediately south through west of island mountains. A jet stream in the upper atmosphere over the region will also produce Moderate Turbulence from FL350 to FL450.
AIRMET Sierra in effect for Mountain Obscurations above 020 for north and east sections of Kauai, Oahu, Maui and the Big Island. This AIRMET may continue through the early morning hours.
AIRMET Tango in effect for Moderate Turbulence over and immediately south through west of island mountains.
AIRMET Tango in effect for Moderate Turbulence across the region from FL350 to FL450.

Marine

Strong high pressure lies north of the state producing fresh to locally strong trade winds across the area. A Small Craft Advisory remains in effect for the typically windy waters around Maui County and the Big Island, and has been expanded to include Kauai Northwest Waters, Oahu Leeward Waters, Kaiwi Channel and Maui County Leeward Waters. Expect these conditions to persist into the weekend.
Short period choppy surf will dominate the wave spectrum through the remainder of the week and on into early next week due to a long fetch of easterly winds over and upwind of the state. A series of small southerly swells will keep surf on the small side throughout the forecast period. North facing shores may see some trade wind swell wrap and west facing shores will see some south swell wrap. No other significant swells are expected.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, 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.