Weather Forecast

Maui Weather Forecast for July 21, 2021

July 21, 2021, 7:15 AM HST
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Photo Credit: Jeni Ji Cousins

West Side

Today: Mostly sunny, with a high near 88. Windy, with an east northeast wind 20 to 23 mph, with gusts as high as 32 mph.

Tonight: Partly cloudy, with a low around 72. Windy, with an east northeast wind around 24 mph, with gusts as high as 34 mph.

Thursday: Sunny, with a high near 88. Windy, with an east northeast wind 21 to 23 mph, with gusts as high as 32 mph.

South Side

Today: Mostly sunny, with a high near 89. Calm wind becoming south southwest 5 to 8 mph in the morning.

Tonight: Mostly clear, with a low around 71. South wind 5 to 7 mph becoming calm after midnight.

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Thursday: Sunny, with a high near 89. Calm wind becoming west northwest 5 to 7 mph.

North Shore

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Today: Scattered showers before noon. Mostly sunny, with a high near 86. Windy, with an east northeast wind 20 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers. Mostly cloudy, with a low around 72. Windy, with an east northeast wind 21 to 24 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Thursday: Scattered showers, mainly before noon. Mostly sunny, with a high near 86. Breezy, with an east northeast wind around 20 mph, with gusts as high as 28 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

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Today: Isolated showers before noon. Mostly sunny, with a high near 87. Breezy, with a northeast wind 15 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 20%.

Tonight: Partly cloudy, with a low around 70. Breezy, with a north northeast wind 17 to 22 mph, with gusts as high as 31 mph.

Thursday: Isolated showers before noon. Mostly sunny, with a high near 87. Breezy, with a northeast wind 16 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 20%.

Upcountry

Today: Mostly sunny, with a high near 75. West wind 5 to 8 mph.

Tonight: Mostly clear, with a low around 58. Southeast wind 3 to 7 mph.

Thursday: Sunny, with a high near 75. Calm wind becoming west 5 to 7 mph in the morning.

East Maui

Today: Scattered showers. Partly sunny, with a high near 80. East wind 9 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 69. East wind 9 to 11 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Thursday: Showers likely, mainly between 7am and 1pm. Partly sunny, with a high near 80. East wind 9 to 13 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Lanai City

Today: Isolated showers after 1pm. Mostly sunny, with a high near 79. Windy, with a northeast wind 21 to 24 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Tonight: Isolated showers before 7pm. Partly cloudy, with a low around 67. Windy, with a northeast wind 16 to 24 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Thursday: Isolated showers between 7am and 1pm. Mostly sunny, with a high near 78. Windy, with a northeast wind 18 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 20%.

Kaunakakai

Today: Mostly sunny, with a high near 87. Breezy, with an east northeast wind around 16 mph, with gusts as high as 22 mph.

Tonight: Partly cloudy, with a low around 74. East wind 6 to 13 mph.

Thursday: Sunny, with a high near 86. East wind 10 to 14 mph, with gusts as high as 18 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.

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Data Courtesy of NOAA.gov

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